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From abu...@apache.org
Subject [36/52] [abbrv] [partial] kudu git commit: Updating web site for Kudu 1.8.0 release
Date Fri, 26 Oct 2018 18:57:29 GMT
http://git-wip-us.apache.org/repos/asf/kudu/blob/1fefa84c/docs/prior_release_notes.html
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-title: Apache Kudu Prior Version Release Notes
-layout: default
-active_nav: docs
-last_updated: 'Last updated 2018-06-15 07:22:05 PDT'
----
-<!--
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-Licensed under the Apache License, Version 2.0 (the "License");
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-    http://www.apache.org/licenses/LICENSE-2.0
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-Unless required by applicable law or agreed to in writing, software
-distributed under the License is distributed on an "AS IS" BASIS,
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--->
-
-
-<div class="container">
-  <div class="row">
-    <div class="col-md-9">
-
-<h1>Apache Kudu Prior Version Release Notes</h1>
-      <div id="preamble">
-<div class="sectionbody">
-<div class="paragraph">
-<p>This section reproduces the release notes for new features and incompatible
-changes in prior releases of Apache Kudu.</p>
-</div>
-<div class="admonitionblock note">
-<table>
-<tr>
-<td class="icon">
-<i class="fa icon-note" title="Note"></i>
-</td>
-<td class="content">
-The list of known issues and limitations for prior releases are not
-reproduced on this page. Please consult the
-<a href="http://kudu.apache.org/releases/">documentation of the appropriate release</a>
-for a list of known issues and limitations.
-</td>
-</tr>
-</table>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.6.0_upgrade_notes"><a class="link" href="#rn_1.6.0_upgrade_notes">Upgrade Notes</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>Upgrading directly from Kudu 1.5.0 is supported and no special upgrade steps
-are required. A rolling upgrade may work, however it has not been tested.
-When upgrading Kudu, it is recommended to first shut down all Kudu processes
-across the cluster, then upgrade the software on all servers, then restart
-the Kudu processes on all servers in the cluster.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.6.0_obsoletions"><a class="link" href="#rn_1.6.0_obsoletions">Obsoletions</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>Support for Spark 1 (kudu-spark_2.10) has been <strong>removed</strong> in Kudu 1.6.0 and
-now only Spark 2 is supported. Spark 1 support was deprecated in Kudu 1.5.0.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.6.0_deprecations"><a class="link" href="#rn_1.6.0_deprecations">Deprecations</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>Support for Java 7 has been deprecated since Kudu 1.5.0 and may be removed in
-the next major release.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.6.0_new_features"><a class="link" href="#rn_1.6.0_new_features">New features</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>Tablet servers' tolerance of disk failures is now enabled by default and has
-been extended to handle data directory failures at runtime. In the event of
-a disk failure at runtime, any tablets with data on a failed disk will be
-shut down and restarted on another tablet server. There is a configurable
-tradeoff between a newly added tablet&#8217;s tolerance to disk failures and its
-ability to parallelize reads via the experimental
-<code>--fs_target_data_dirs_per_tablet</code> flag. Tablets that are spread across fewer
-disks are less likely to be affected by a disk failure, at the cost of
-reduced parallelism. By default, tablets are striped across all available
-disks. Note that the first configured data directory and the WAL directory
-cannot currently tolerate disk failures. This will be further improved in
-future Kudu releases.</p>
-</li>
-<li>
-<p>Kudu servers can now adopt new data directories via the new
-<code>kudu fs update_dirs</code> tool. The new directory will be used by new tablet
-replicas only. Note that removing directories is not yet supported
-(see <a href="https://issues.apache.org/jira/browse/KUDU-2202">KUDU-2202</a>).</p>
-</li>
-<li>
-<p>Kudu servers have two new flags to control webui TLS/HTTPS
-settings: <code>--webserver_tls_ciphers</code> and <code>--webserver_tls_min_protocol</code>.
-These flags allow the advertised TLS ciphers and TLS protocol versions to be
-configured. Additionally, the webserver now excludes insecure legacy ciphers
-by default
-(see <a href="https://issues.apache.org/jira/browse/KUDU-2190">KUDU-2190</a>).</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="_optimizations_and_improvements"><a class="link" href="#_optimizations_and_improvements">Optimizations and improvements</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>Kudu servers can now tolerate short interruptions in NTP clock
-synchronization. NTP synchronization is still required when any Kudu daemon
-starts up. If NTP synchronization is not available, diagnostic information
-is now logged to help pinpoint the issue
-(see <a href="https://issues.apache.org/jira/browse/KUDU-1578">KUDU-1578</a>).</p>
-</li>
-<li>
-<p>Tablet server startup time has been improved significantly on servers
-containing large numbers of blocks.</p>
-</li>
-<li>
-<p>The log block manager now performs disk data deletion in batches. This
-optimization can significantly reduce the time taken to delete data on a tablet.</p>
-</li>
-<li>
-<p>The usage of sensitive data redaction flag has been slightly changed. By
-setting <code>--redact=log</code> flag, redaction will be disabled in the web UI but
-retained for server logs. Alternatively, <code>--redact=none</code> can be used to
-disable redaction completely.</p>
-</li>
-<li>
-<p>The Spark DataSource integration now can take advantage of scan locality
-for better scan performance, the scan will take place at the closest replica
-instead of going to the leader.</p>
-</li>
-<li>
-<p>Various optimizations were made to reduce the 99th percentile latency of
-writes on the tablet server. This can also improve throughput on certain
-write workloads, particularly on larger clusters.</p>
-</li>
-<li>
-<p>Kudu may now be configured to ignore system-wide auth_to_local mappings
-configured in /etc/krb5.conf by setting the configuration flag
-<code>--use_system_auth_to_local=false</code>
-(see <a href="https://issues.apache.org/jira/browse/KUDU-2198">KUDU-2198</a>).</p>
-</li>
-<li>
-<p>The performance of the compaction scheduler has been improved. In
-previous versions, certain types of time series workloads were found to
-cause compaction scheduling to take tens of seconds. These workloads now
-schedule compactions an order of magnitude more efficiently.</p>
-</li>
-<li>
-<p>The compaction scheduler has been improved to avoid running a compaction
-when the benefit of that compaction is extremely small.</p>
-</li>
-<li>
-<p>Tablet servers now consider the health of all replicas of a tablet before
-deciding to evict one. This can improve stability of the Kudu cluster after
-experiencing multiple simultaneous daemon failures
-(see <a href="https://issues.apache.org/jira/browse/KUDU-2048">KUDU-2048</a>).</p>
-</li>
-<li>
-<p>Several performance improvements have been made to the Kudu master,
-particularly in concurrency of clients opening tables. This should improve
-performance in highly concurrent workloads.</p>
-</li>
-<li>
-<p>The on-disk size metric for a tablet now includes all data and metadata.
-Previously, it excluded WAL segments and consensus metadata
-(see <a href="https://issues.apache.org/jira/browse/KUDU-1755">KUDU-1755</a>).</p>
-</li>
-<li>
-<p>Added verbose mode for the 'kudu cluster ksck' command to enable output
-of detailed information on the cluster&#8217;s metadata, even when no errors are
-detected.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.6.0_fixed_issues"><a class="link" href="#rn_1.6.0_fixed_issues">Fixed Issues</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>HybridTime timestamp propagation now works in the Java client when using scan
-tokens (see <a href="https://issues.apache.org/jira/browse/KUDU-1411">KUDU-1411</a>).</p>
-</li>
-<li>
-<p>Fixed an error message commonly found in tablet server logs indicating that
-operations were being read "from the future"
-(see <a href="https://issues.apache.org/jira/browse/KUDU-1078">KUDU-1078</a>).</p>
-</li>
-<li>
-<p>Tombstoned tablets no longer report metrics
-(see <a href="https://issues.apache.org/jira/browse/KUDU-2044">KUDU-2044</a>).</p>
-</li>
-<li>
-<p>Fixed a bug in the C++ client which could cause tablets to be erroneously
-pruned, or skipped, during certain scans, resulting in fewer results than
-expected being returned from queries. The bug only affected tables whose range
-partition columns are a proper prefix of the primary key
-(see <a href="https://issues.apache.org/jira/browse/KUDU-2173">KUDU-2173</a>).</p>
-</li>
-<li>
-<p>Published Kudu Java artifacts are now fully compatible with JRE 7 and JRE 8.
-There was previously a bug in the release process which made them compatible
-only with JRE 8
-(see <a href="https://issues.apache.org/jira/browse/KUDU-2188">KUDU-2188</a>).</p>
-</li>
-<li>
-<p>Fixed a typo in the list of default TLS ciphers used by Kudu servers. As a
-result, two additional cipher suites are now available:</p>
-<div class="ulist">
-<ul>
-<li>
-<p>ECDHE-RSA-AES128-SHA256 TLSv1.2 Kx=ECDH Au=RSA Enc=AES(128)  Mac=SHA256</p>
-</li>
-<li>
-<p>AES256-GCM-SHA384       TLSv1.2 Kx=RSA  Au=RSA Enc=AESGCM(256) Mac=AEAD</p>
-</li>
-</ul>
-</div>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.6.0_wire_compatibility"><a class="link" href="#rn_1.6.0_wire_compatibility">Wire Protocol compatibility</a></h2>
-<div class="sectionbody">
-<div class="paragraph">
-<p>Kudu 1.6.0 is wire-compatible with previous versions of Kudu:</p>
-</div>
-<div class="ulist">
-<ul>
-<li>
-<p>Kudu 1.6 clients may connect to servers running Kudu 1.0 or later. If the client uses
-features that are not available on the target server, an error will be returned.</p>
-</li>
-<li>
-<p>Rolling upgrade between Kudu 1.5 and Kudu 1.6 servers is believed to be possible
-though has not been sufficiently tested. Users are encouraged to shut down all nodes
-in the cluster, upgrade the software, and then restart the daemons on the new version.</p>
-</li>
-<li>
-<p>Kudu 1.0 clients may connect to servers running Kudu 1.6 with the exception of the
-below-mentioned restrictions regarding secure clusters.</p>
-</li>
-</ul>
-</div>
-<div class="paragraph">
-<p>The authentication features introduced in Kudu 1.3 place the following limitations
-on wire compatibility between Kudu 1.6 and versions earlier than 1.3:</p>
-</div>
-<div class="ulist">
-<ul>
-<li>
-<p>If a Kudu 1.6 cluster is configured with authentication or encryption set to "required",
-clients older than Kudu 1.3 will be unable to connect.</p>
-</li>
-<li>
-<p>If a Kudu 1.6 cluster is configured with authentication and encryption set to "optional"
-or "disabled", older clients will still be able to connect.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.6.0_incompatible_changes"><a class="link" href="#rn_1.6.0_incompatible_changes">Incompatible Changes in Kudu 1.6.0</a></h2>
-<div class="sectionbody">
-<div class="sect2">
-<h3 id="rn_1.6.0_client_compatibility"><a class="link" href="#rn_1.6.0_client_compatibility">Client Library Compatibility</a></h3>
-<div class="ulist">
-<ul>
-<li>
-<p>The Kudu 1.6 Java client library is API- and ABI-compatible with Kudu 1.5. Applications
-written against Kudu 1.5 will compile and run against the Kudu 1.6 client library and
-vice-versa.</p>
-</li>
-<li>
-<p>The Kudu 1.6 C++ client is API- and ABI-forward-compatible with Kudu 1.5.
-Applications written and compiled against the Kudu 1.5 client library will run without
-modification against the Kudu 1.6 client library. Applications written and compiled
-against the Kudu 1.6 client library will run without modification against the Kudu 1.5
-client library.</p>
-</li>
-<li>
-<p>The Kudu 1.6 Python client is API-compatible with Kudu 1.5. Applications
-written against Kudu 1.5 will continue to run against the Kudu 1.6 client
-and vice-versa.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.5.0"><a class="link" href="#rn_1.5.0">Release notes specific to 1.5.0</a></h2>
-<div class="sectionbody">
-
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.5.0_upgrade_notes"><a class="link" href="#rn_1.5.0_upgrade_notes">Upgrade Notes</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>Kudu 1.5 now enables the optional ability to compute, store, and verify
-checksums on all pieces of data stored on a server by default. Due to
-storage format changes, downgrading to versions 1.3 or earlier is not
-supported and will result in an error.</p>
-</li>
-<li>
-<p>Spark 2.2+ requires Java 8 at runtime even though Kudu Spark 2.x integration
-is Java 7 compatible. Spark 2.2 is the default dependency version as of
-Kudu 1.5.0.</p>
-</li>
-<li>
-<p>The kudu-spark-tools module has been renamed to kudu-spark2-tools_2.11 in
-order to include the Spark and Scala base versions. This matches the pattern
-used in the kudu-spark module and artifacts.</p>
-</li>
-<li>
-<p>To improve security, world-readable Kerberos keytab files are no longer
-accepted by default. Set <code>--allow_world_readable_credentials=true</code> to override
-this behavior. See
-<a href="https://issues.apache.org/jira/browse/KUDU-1955">KUDU-1955</a> for additional
-details.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.5.0_deprecations"><a class="link" href="#rn_1.5.0_deprecations">Deprecations</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>Support for Java 7 is deprecated as of Kudu 1.5.0 and may be removed in the
-next major release.</p>
-</li>
-<li>
-<p>Support for Spark 1 (kudu-spark_2.10) is deprecated as of Kudu 1.5.0 and may
-be removed in the next minor release.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.5.0_new_features"><a class="link" href="#rn_1.5.0_new_features">New features</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>Tablet servers are now optionally able to tolerate disk failures at
-startup. This feature is experimental; by default, Kudu will crash if it
-experiences a disk failure. When enabled, tablets with any data on the failed
-disk will not be opened and will be replicated as needed. To enable this, set
-the <code>--crash_on_eio</code> flag to <code>false</code>. Additionally, there is a configurable
-tradeoff between a newly added tablet&#8217;s tolerance to disk failures and its
-parallelization of I/O via the <code>--fs_target_data_dirs_per_tablet</code> flag.
-Tablets that are spread across fewer disks are less likely to be affected by a
-disk failure, at the cost of reduced parallelism. Note that the first
-configured data directory and the WAL directory cannot currently tolerate disk
-failures, and disk failures during run-time are still fatal.</p>
-</li>
-<li>
-<p>Kudu server web UIs have a new configuration dashboard (/config) which
-provides a high level summary of important security configuration values, such
-as whether RPC authentication is required, or web server HTTPS encryption is
-enabled. Other types of configuration will be added in future releases.</p>
-</li>
-<li>
-<p>The <code>kudu</code> command line tool has two new features: <code>kudu tablet change_config
-move_replica</code> and <code>kudu local_replica data_size</code>. The 'tablet change_config
-move_replica' tool moves a tablet replica from one tablet server to another,
-under the condition that the tablet is healthy. An operator can use this tool to
-rebalance tablet replicas between tablet servers. The 'local_replica data size'
-tool summarizes the space usage of a tablet, breaking it down by type of file,
-column, and rowset.</p>
-</li>
-<li>
-<p>kudu-client-tools now supports exporting CSV files and importing
-Apache Parquet files. This feature is unstable and may change APIs and
-functionality in future releases.</p>
-</li>
-<li>
-<p>kudu-spark-tools now supports importing and exporting CSV, Apache Avro and
-Apache Parquet files. This feature is unstable and may change APIs and
-functionality in future releases.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.5.0_optimizations_improvements"><a class="link" href="#rn_1.5.0_optimizations_improvements">Optimizations and improvements</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>The log block manager now performs disk synchronization in batches.
-This optimization can significantly reduce the time taken to copy tablet data
-from one server to another; in one case tablet copy time is reduced by 35%.
-It also improves the general performance of flushes and compactions.</p>
-</li>
-<li>
-<p>A new feature referred to as "tombstoned voting" is added to the Raft
-consensus subsystem to allow tablet replicas in the <code>TABLET_DATA_TOMBSTONED</code>
-state to vote in tablet leader elections. This feature increases Kudu&#8217;s
-stability and availability by improving the likelihood that Kudu will be able
-to self-heal in more edge-case scenarios, such as when tablet copy operations
-fail. See <a href="https://issues.apache.org/jira/browse/KUDU-871">KUDU-871</a> for
-details.</p>
-</li>
-<li>
-<p>The tablet on-disk size metric has been made more accurate. Previously, the
-metric included only REDO deltas; it now counts all deltas. Additionally, the
-metric includes the size of bloomfiles, ad hoc indexes, and the tablet
-superblock. WAL segments and consensus metadata are still not counted. The
-latter is very small compared to the size of data, but the former may be
-significant depending on the workload (this will be resolved in a future
-release).</p>
-</li>
-<li>
-<p>The number of threads used by the Kudu tablet server has been further reduced.
-Previously, each follower tablet replica used a dedicated thread to detect
-leader tablet replica failures, and each leader replica used one dedicated
-thread per follower to send Raft heartbeats to that follower. The work
-performed by these dedicated threads has been reassigned to other threads.
-Other improvements were made to facilitate better thread sharing by tablets.
-For the purpose of capacity planning, expect the Kudu tablet server to create
-one thread for every five "cold" (i.e. those not servicing writes) tablets,
-and an additional three threads for every "hot" tablet. This will be further
-improved upon in future Kudu releases.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.5.0_fixed_issues"><a class="link" href="#rn_1.5.0_fixed_issues">Fixed Issues</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>The Java Kudu client now automatically requests new authentication tokens
-after expiration. As a result, long-lived Java clients are now supported. See
-<a href="https://issues.apache.org/jira/browse/KUDU-2013">KUDU-2013</a> for more
-details.</p>
-</li>
-<li>
-<p>Multiple Kerberos compatibility bugs have been fixed, including support
-for environments with disabled reverse DNS, FreeIPA compatibility, principal
-names including uppercase characters, and hosts without a FQDN.</p>
-</li>
-<li>
-<p>A bug in the binary prefix decoder which could cause a tablet server 'check'
-assertion crash has been fixed. The crash could only be triggered in very
-specific scenarios; see
-<a href="https://issues.apache.org/jira/browse/KUDU-2085">KUDU-2085</a> for additional
-details.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.5.0_wire_compatibility"><a class="link" href="#rn_1.5.0_wire_compatibility">Wire Protocol compatibility</a></h2>
-<div class="sectionbody">
-<div class="paragraph">
-<p>Kudu 1.5.0 is wire-compatible with previous versions of Kudu:</p>
-</div>
-<div class="ulist">
-<ul>
-<li>
-<p>Kudu 1.5 clients may connect to servers running Kudu 1.0 or later. If the client uses
-features that are not available on the target server, an error will be returned.</p>
-</li>
-<li>
-<p>Rolling upgrade between Kudu 1.4 and Kudu 1.5 servers is believed to be possible
-though has not been sufficiently tested. Users are encouraged to shut down all nodes
-in the cluster, upgrade the software, and then restart the daemons on the new version.</p>
-</li>
-<li>
-<p>Kudu 1.0 clients may connect to servers running Kudu 1.5 with the exception of the
-below-mentioned restrictions regarding secure clusters.</p>
-</li>
-</ul>
-</div>
-<div class="paragraph">
-<p>The authentication features introduced in Kudu 1.3 place the following limitations
-on wire compatibility between Kudu 1.5 and versions earlier than 1.3:</p>
-</div>
-<div class="ulist">
-<ul>
-<li>
-<p>If a Kudu 1.5 cluster is configured with authentication or encryption set to "required",
-clients older than Kudu 1.3 will be unable to connect.</p>
-</li>
-<li>
-<p>If a Kudu 1.5 cluster is configured with authentication and encryption set to "optional"
-or "disabled", older clients will still be able to connect.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.5.0_incompatible_changes"><a class="link" href="#rn_1.5.0_incompatible_changes">Incompatible Changes in Kudu 1.5.0</a></h2>
-<div class="sectionbody">
-<div class="sect2">
-<h3 id="rn_1.5.0_client_compatibility"><a class="link" href="#rn_1.5.0_client_compatibility">Client Library Compatibility</a></h3>
-<div class="ulist">
-<ul>
-<li>
-<p>The Kudu 1.5 Java client library is API- and ABI-compatible with Kudu 1.4. Applications
-written against Kudu 1.4 will compile and run against the Kudu 1.5 client library and
-vice-versa, unless one of the following newly added APIs is used:</p>
-</li>
-<li>
-<p>The Kudu 1.5 C++ client is API- and ABI-forward-compatible with Kudu 1.4.
-Applications written and compiled against the Kudu 1.4 client library will run without
-modification against the Kudu 1.5 client library. Applications written and compiled
-against the Kudu 1.5 client library will run without modification against the Kudu 1.4
-client library.</p>
-</li>
-<li>
-<p>The Kudu 1.5 Python client is API-compatible with Kudu 1.4. Applications
-written against Kudu 1.4 will continue to run against the Kudu 1.5 client
-and vice-versa.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.4.0"><a class="link" href="#rn_1.4.0">Release notes specific to 1.4.0</a></h2>
-<div class="sectionbody">
-
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.4.0_upgrade_notes"><a class="link" href="#rn_1.4.0_upgrade_notes">Upgrade Notes</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>The Maintenance Manager now fully uses the threads it&#8217;s given (see the improvements
-described further below), so it&#8217;s now able to generate a lot more IO by flushing and
-compacting more often. Generally, the recommended ratio of MM threads to data
-directories is 1:3; operators of clusters above that ratio should be mindful of
-this when upgrading.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.4.0_new_features"><a class="link" href="#rn_1.4.0_new_features">New features</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>The C++ and Java client libraries now support the ability to alter the
-storage attributes (e.g. encoding and compression) and default value
-of existing columns. Additionally, it is now possible to rename
-a column which is part of a table&#8217;s primary key.</p>
-</li>
-<li>
-<p>The C++ client library now includes an experimental <code>KuduPartitioner</code> API which may
-be used to efficiently map rows to their associated partitions and hosts.
-This may be used to achieve better locality or distribution of writes
-in client applications.</p>
-</li>
-<li>
-<p>The Java client library now supports enabling fault tolerance on scanners.
-Fault tolerant scanners are able to transparently recover from concurrent
-server crashes at the cost of some performance overhead. See the Java
-API documentation for more details on usage.</p>
-</li>
-<li>
-<p>The <code>kudu</code> command line tool now includes a new advanced administrative
-command <code>kudu remote_replica unsafe_change_config</code>. This command may be used
-to force a tablet to perform an unsafe change of its Raft replication
-configuration. This can be used to recover from scenarios such as a loss
-of a majority of replicas, at the risk of losing edits.</p>
-</li>
-<li>
-<p>The <code>kudu</code> command line tool now includes the <code>kudu fs check</code> command
-which performs various offline consistency checks on the local on-disk
-storage of a Kudu Tablet Server or Master. In addition to detecting
-various inconsistencies or corruptions, it can also detect and remove
-data blocks that are no longer referenced by any tablet but were not
-fully removed from disk due to a crash or a bug in prior versions of Kudu.</p>
-</li>
-<li>
-<p>The <code>kudu</code> command line tool can now be used to list the addresses and
-identifiers of the servers in the cluster using either <code>kudu master list</code>
-or <code>kudu tserver list</code>.</p>
-</li>
-<li>
-<p>Kudu 1.4 now includes the optional ability to compute, store, and verify
-checksums on all pieces of data stored on a server. Prior versions only
-performed checksums on certain portions of the stored data. This feature
-is not enabled by default since it makes a backward-incompatible change
-to the on-disk formats and thus prevent downgrades. Kudu 1.5 will enable
-the feature by default.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="_optimizations_and_improvements_2"><a class="link" href="#_optimizations_and_improvements_2">Optimizations and improvements</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p><code>kudu cluster ksck</code> now detects and reports new classes of
-inconsistencies and issues. In particular, it is better able to
-detect cases where a configuration change such as a replica eviction
-or addition is pending but is unable to be committed. It also now
-properly detects and reports cases where a tablet has no elected
-leader.</p>
-</li>
-<li>
-<p>The default size for Write Ahead Log (WAL) segments has been reduced
-from 64MB to 8MB. Additionally, in the case that all replicas of a
-tablet are fully up to date and data has been flushed from memory,
-servers will now retain only a single WAL segment rather than
-two. These changes are expected to reduce the average consumption of
-disk space on the configured WAL disk by 16x, as well as improve the
-startup speed of tablet servers by reducing the number and size of
-WAL segments that need to be re-read.</p>
-</li>
-<li>
-<p>The default on-disk storage system used by Kudu servers (Log Block Manager)
-has been improved to compact its metadata and remove dead containers.
-This compaction and garbage collection occurs only at startup. Thus, the
-first startup after upgrade is expected to be longer than usual, and
-subsequent restarts should be shorter.</p>
-</li>
-<li>
-<p>The usability of the Kudu web interfaces has been improved,
-particularly for the case where a server hosts many tablets or a
-table has many partitions. Pages that list tablets now include
-a top-level summary of tablet status and show the complete list
-under a toggleable section.</p>
-</li>
-<li>
-<p>The Maintenance Manager has been improved to improve utilization of the
-configured maintenance threads. Previously, maintenance work would
-only be scheduled a maximum of 4 times per second, but now maintenance
-work will be scheduled immediately whenever any configured thread is
-available. This can improve the throughput of write-heavy workloads.</p>
-</li>
-<li>
-<p>The Maintenance Manager will now aggressively schedule flushes of
-in-memory data when memory consumption crosses 60% of the configured
-process-wide memory limit. The backpressure mechanism which begins
-to throttle client writes has been accordingly adjusted to not begin
-throttling until reaching 80% of the configured limit. These two
-changes together result in improved write throughput, more consistent
-latency, and fewer timeouts due to memory exhaustion.</p>
-</li>
-<li>
-<p>Many performance improvements were made to write performance. Applications
-which send large batches of writes to Kudu should see substantially
-improved throughput in Kudu 1.4.</p>
-</li>
-<li>
-<p>Several improvements were made to reduce the memory consumption of
-Kudu Tablet Servers which hold large volumes of data. The specific
-amount of memory saved varies depending on workload, but the expectation
-is that approximately 350MB of excess peak memory usage has been eliminated
-per TB of data stored.</p>
-</li>
-<li>
-<p>The number of threads used by the Kudu Tablet Server has been reduced.
-Previously, each tablet used a dedicated thread to append to its WAL.
-Those threads now automatically stop running if there is no activity
-on a given tablet for a short period of time.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.4.0_fixed_issues"><a class="link" href="#rn_1.4.0_fixed_issues">Fixed Issues</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-2020">KUDU-2020</a>
-Fixed an issue where re-replication after a failure would proceed
-significantly slower than expected. This bug caused many tablets
-to be unnecessarily copied multiple times before successfully
-being considered re-replicated, resulting in significantly more
-network and IO bandwidth usage than expected. Mean time to recovery
-on clusters with large amounts of data is improved by up to 10x by this
-fix.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1982">KUDU-1982</a>
-Fixed an issue where the Java client would call <code>NetworkInterface.getByInetAddress</code>
-very often, causing performance problems particularly on Windows
-where this function can be quite slow.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1755">KUDU-1755</a>
-Improved the accuracy of the <code>on_disk_size</code> replica metrics to
-include the size consumed by bloom filters, primary key indexes,
-and superblock metadata, and delta files. Note that, because the size
-metric is now more accurate, the reported values are expected to
-increase after upgrading to Kudu 1.4. This does not indicate that
-replicas are using more space after the upgrade; rather, it is
-now accurately reporting the amount of space that has always been
-used.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1192">KUDU-1192</a>
-Kudu servers will now periodically flush their log messages to disk
-even if no <code>WARNING</code>-level messages have been logged. This makes it
-easier to tail the logs to see progress output during normal startup.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1999">KUDU-1999</a>
-Fixed the ability to run Spark jobs in "cluster" mode against
-Kudu clusters secured by Kerberos.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.4.0_wire_compatibility"><a class="link" href="#rn_1.4.0_wire_compatibility">Wire Protocol compatibility</a></h2>
-<div class="sectionbody">
-<div class="paragraph">
-<p>Kudu 1.4.0 is wire-compatible with previous versions of Kudu:</p>
-</div>
-<div class="ulist">
-<ul>
-<li>
-<p>Kudu 1.4 clients may connect to servers running Kudu 1.0 or later. If the client uses
-features that are not available on the target server, an error will be returned.</p>
-</li>
-<li>
-<p>Kudu 1.0 clients may connect to servers running Kudu 1.4 with the exception of the
-below-mentioned restrictions regarding secure clusters.</p>
-</li>
-<li>
-<p>Rolling upgrade between Kudu 1.3 and Kudu 1.4 servers is believed to be possible
-though has not been sufficiently tested. Users are encouraged to shut down all nodes
-in the cluster, upgrade the software, and then restart the daemons on the new version.</p>
-</li>
-</ul>
-</div>
-<div class="paragraph">
-<p>The authentication features introduced in Kudu 1.3 place the following limitations
-on wire compatibility between Kudu 1.4 and versions earlier than 1.3:</p>
-</div>
-<div class="ulist">
-<ul>
-<li>
-<p>If a Kudu 1.4 cluster is configured with authentication or encryption set to "required",
-clients older than Kudu 1.3 will be unable to connect.</p>
-</li>
-<li>
-<p>If a Kudu 1.4 cluster is configured with authentication and encryption set to "optional"
-or "disabled", older clients will still be able to connect.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.4.0_incompatible_changes"><a class="link" href="#rn_1.4.0_incompatible_changes">Incompatible Changes in Kudu 1.4.0</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>Kudu servers, by default, will now only allow unencrypted or unauthenticated connections
-from trusted subnets, which are private networks (127.0.0.0/8,10.0.0.0/8,172.16.0.0/12,
-192.168.0.0/16,169.254.0.0/16) and local subnets of all local network interfaces.
-Unencrypted or unauthenticated connections from publicly routable IPs will be rejected,
-even if encryption and authentication are not configured.</p>
-<div class="paragraph">
-<p>The trusted subnets can be configured using the <code>--trusted_subnets</code> flag, which can be set
-   to IP blocks represented in CIDR notation separated by comma. Set it to '0.0.0.0/0' to
-   allow unauthenticated connections from all remote IP addresses. However, if network access
-   is not otherwise restricted by a firewall, malicious users may be able to gain unauthorized
-   access. This can be mitigated if authentication and encryption are configured to be
-   required.</p>
-</div>
-</li>
-</ul>
-</div>
-<div class="sect2">
-<h3 id="rn_1.4.0_client_compatibility"><a class="link" href="#rn_1.4.0_client_compatibility">Client Library Compatibility</a></h3>
-<div class="ulist">
-<ul>
-<li>
-<p>The Kudu 1.4 Java client library is API- and ABI-compatible with Kudu 1.3. Applications
-written against Kudu 1.3 will compile and run against the Kudu 1.4 client library and
-vice-versa, unless one of the following newly added APIs is used:</p>
-<div class="ulist">
-<ul>
-<li>
-<p><code>[Async]KuduScannerBuilder.setFaultTolerant(&#8230;&#8203;)</code></p>
-</li>
-<li>
-<p>New methods in <code>AlterTableOptions</code>: <code>removeDefault</code>, <code>changeDefault</code>, <code>changeDesiredBlockSize</code>,
-<code>changeEncoding</code>, <code>changeCompressionAlgorithm</code></p>
-</li>
-<li>
-<p><code>KuduClient.updateLastPropagatedTimestamp</code></p>
-</li>
-<li>
-<p><code>KuduClient.getLastPropagatedTimestamp</code></p>
-</li>
-<li>
-<p>New getters in <code>PartialRow</code>: <code>getBoolean</code>, <code>getByte</code>, <code>getShort</code>, <code>getInt</code>, <code>getLong</code>,
-<code>getFloat</code>, <code>getDouble</code>, <code>getString</code>, <code>getBinaryCopy</code>, <code>getBinary</code>, <code>isNull</code>,
-<code>isSet</code>.</p>
-</li>
-</ul>
-</div>
-</li>
-<li>
-<p>The Kudu 1.4 C++ client is API- and ABI-forward-compatible with Kudu 1.3.
-Applications written and compiled against the Kudu 1.3 client library will run without
-modification against the Kudu 1.4 client library. Applications written and compiled
-against the Kudu 1.4 client library will run without modification against the Kudu 1.3
-client library unless they use one of the following new APIs:</p>
-<div class="ulist">
-<ul>
-<li>
-<p><code>KuduPartitionerBuilder</code></p>
-</li>
-<li>
-<p>`KuduPartitioner</p>
-</li>
-<li>
-<p><code>KuduScanner::SetRowFormatFlags</code> (unstable API)</p>
-</li>
-<li>
-<p><code>KuduScanBatch::direct_data</code>, <code>KuduScanBatch::indirect_data</code> (unstable API)</p>
-</li>
-</ul>
-</div>
-</li>
-<li>
-<p>The Kudu 1.4 Python client is API-compatible with Kudu 1.3. Applications
-written against Kudu 1.3 will continue to run against the Kudu 1.4 client
-and vice-versa.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.3.0"><a class="link" href="#rn_1.3.0">Release notes specific to 1.3.0</a></h2>
-<div class="sectionbody">
-
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.3.0_new_features"><a class="link" href="#rn_1.3.0_new_features">New features</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>Kudu 1.3 adds support for strong authentication based on Kerberos. This optional feature
-allows users to authenticate themselves using Kerberos tickets, and also provides
-mutual authentication of servers using Kerberos credentials stored in keytabs. This
-feature is optional, but recommended for deployments requiring security.</p>
-</li>
-<li>
-<p>Kudu 1.3 adds support for encryption of data on the network using Transport Layer Security
-(TLS). Kudu will now use TLS to encrypt all network traffic between clients and servers as
-well as any internal traffic among servers, with the exception of traffic determined to
-be within a localhost network connection. Encryption is enabled by default whenever it can
-be determined that both the client and server support the feature.</p>
-</li>
-<li>
-<p>Kudu 1.3 adds coarse-grained service-level authorization of access to the cluster.
-The operator may set up lists of permitted users who may act as administrators and
-as clients of the cluster. Combined with the strong authentication feature described
-above, this can enable a secure environment for some use cases. Note that fine-grained
-access control (e.g. table-level or column-level) is not yet supported.</p>
-</li>
-<li>
-<p>Kudu 1.3 adds a background task to tablet servers which removes historical versions of
-data which have fallen behind the configured data retention time. This reduces disk space
-usage in all workloads, but particularly in those with a higher volume of updates or
-upserts.</p>
-</li>
-<li>
-<p>Kudu now incorporates Google Breakpad, a library which writes crash reports in
-the case of a server crash. These reports can be found within the configured log directory,
-and can be useful during bug diagnosis.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="_optimizations_and_improvements_3"><a class="link" href="#_optimizations_and_improvements_3">Optimizations and improvements</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>Kudu servers will now change the file permissions of data directories and contained
-data files based on a new configuration flag <code>--umask</code>. As a result, after upgrading,
-permissions on disk may be more restrictive than in previous versions. The new default
-configuration improves data security.</p>
-</li>
-<li>
-<p>Kudu&#8217;s web UI will now redact strings which may include sensitive user data. For example,
-the monitoring page which shows in-progress scans no longer includes the scanner predicate
-values. The tracing and RPC diagnostics endpoints no longer include contents of RPCs which
-may include table data.</p>
-</li>
-<li>
-<p>By default, Kudu now reserves 1% of each configured data volume as free space. If a volume
-is seen to have less than 1% of disk space free, Kudu will stop writing to that volume
-to avoid completely filling up the disk.</p>
-</li>
-<li>
-<p>The default encoding for numeric columns (int, float, and double) has been changed
-to <code>BIT_SHUFFLE</code>. The default encoding for binary and string columns has been
-changed to <code>DICT_ENCODING</code>. Dictionary encoding automatically falls back to the old
-default (<code>PLAIN</code>) when cardinality is too high to be effectively encoded.</p>
-<div class="paragraph">
-<p>These new defaults match the default behavior of other storage mechanisms such as
-  Apache Parquet and are likely to perform better out of the box.</p>
-</div>
-</li>
-<li>
-<p>Kudu now uses <code>LZ4</code> compression when writing its Write Ahead Log (WAL). This improves
-write performance and stability for many use cases.</p>
-</li>
-<li>
-<p>Kudu now uses <code>LZ4</code> compression when writing delta files. This can improve both
-read and write performance as well as save substantial disk usage, especially
-for workloads involving a high number of updates or upserts containing compressible
-data.</p>
-</li>
-<li>
-<p>The Kudu API now supports the ability to express <code>IS NULL</code> and <code>IS NOT NULL</code> predicates
-on scanners. The Spark DataSource integration will take advantage of these new
-predicates when possible.</p>
-</li>
-<li>
-<p>Both C++ and Java clients have been optimized to prune partitions more effectively
-when performing scans using the <code>IN (&#8230;&#8203;)</code> predicate.</p>
-</li>
-<li>
-<p>The exception messages produced by the Java client are now truncated to a maximum length
-of 32KB.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.3.0_fixed_issues"><a class="link" href="#rn_1.3.0_fixed_issues">Fixed Issues</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1893">KUDU-1893</a>
-Fixed a critical bug in which wrong results would be returned when evaluating
-predicates applied to columns added using the <code>ALTER TABLE</code> operation.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1905">KUDU-1905</a>
-Fixed a crash after inserting a row sharing a primary key with a recently-deleted
-row in tables where the primary key is comprised of all of the columns.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1899">KUDU-1899</a>
-Fixed a crash after inserting a row with an empty string as the single-column
-primary key.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1904">KUDU-1904</a>
-Fixed a potential crash when performing random reads against a column using RLE
-encoding and containing long runs of NULL values.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1853">KUDU-1853</a>
-Fixed an issue where disk space could be leaked on servers which experienced an error
-during the process of copying tablet data from another server.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1856">KUDU-1856</a>
-Fixed an issue in which disk space could be leaked by Kudu servers storing data on
-partitions using the XFS file system. Any leaked disk space will be automatically
-recovered upon upgrade.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1888">KUDU-1888</a>,
-<a href="https://issues.apache.org/jira/browse/KUDU-1906">KUDU-1906</a>
-Fixed multiple issues in the Java client where operation callbacks would never be
-triggered, causing the client to hang.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.3.0_wire_compatibility"><a class="link" href="#rn_1.3.0_wire_compatibility">Wire Protocol compatibility</a></h2>
-<div class="sectionbody">
-<div class="paragraph">
-<p>Kudu 1.3.0 is wire-compatible with previous versions of Kudu:</p>
-</div>
-<div class="ulist">
-<ul>
-<li>
-<p>Kudu 1.3 clients may connect to servers running Kudu 1.0. If the client uses features
-that are not available on the target server, an error will be returned.</p>
-</li>
-<li>
-<p>Kudu 1.0 clients may connect to servers running Kudu 1.3 with the exception of the
-below-mentioned restrictions regarding secure clusters.</p>
-</li>
-<li>
-<p>Rolling upgrade between Kudu 1.2 and Kudu 1.3 servers is believed to be possible
-though has not been sufficiently tested. Users are encouraged to shut down all nodes
-in the cluster, upgrade the software, and then restart the daemons on the new version.</p>
-</li>
-</ul>
-</div>
-<div class="paragraph">
-<p>The authentication features newly introduced in Kudu 1.3 place the following limitations
-on wire compatibility with older versions:</p>
-</div>
-<div class="ulist">
-<ul>
-<li>
-<p>If a Kudu 1.3 cluster is configured with authentication or encryption set to "required",
-older clients will be unable to connect.</p>
-</li>
-<li>
-<p>If a Kudu 1.3 cluster is configured with authentication and encryption set to "optional"
-or "disabled", older clients will still be able to connect.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.3.0_incompatible_changes"><a class="link" href="#rn_1.3.0_incompatible_changes">Incompatible Changes in Kudu 1.3.0</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>Due to storage format changes in Kudu 1.3, downgrade from Kudu 1.3 to earlier versions
-is not supported. After upgrading to Kudu 1.3, attempting to restart with an earlier
-version will result in an error.</p>
-</li>
-<li>
-<p>In order to support running MapReduce and Spark jobs on secure clusters, these
-frameworks now connect to the cluster at job submission time to retrieve authentication
-credentials which can later be used by the tasks to be spawned. This means that
-the process submitting jobs to Kudu clusters must have direct access to that cluster.</p>
-</li>
-<li>
-<p>The embedded web servers in Kudu processes now specify the <code>X-Frame-Options: DENY</code> HTTP
-header which prevents embedding Kudu web pages in HTML <code>iframe</code> elements.</p>
-</li>
-</ul>
-</div>
-<div class="sect2">
-<h3 id="rn_1.3.0_client_compatibility"><a class="link" href="#rn_1.3.0_client_compatibility">Client Library Compatibility</a></h3>
-<div class="ulist">
-<ul>
-<li>
-<p>The Kudu 1.3 Java client library is API- and ABI-compatible with Kudu 1.2. Applications
-written against Kudu 1.2 will compile and run against the Kudu 1.3 client library and
-vice-versa, unless one of the following newly added APIs is used:</p>
-<div class="ulist">
-<ul>
-<li>
-<p><code>[Async]KuduClient.exportAuthenticationCredentials(&#8230;&#8203;)</code> (unstable API)</p>
-</li>
-<li>
-<p><code>[Async]KuduClient.importAuthenticationCredentials(&#8230;&#8203;)</code> (unstable API)</p>
-</li>
-<li>
-<p><code>[Async]KuduClient.getMasterAddressesAsString()</code></p>
-</li>
-<li>
-<p><code>KuduPredicate.newIsNotNullPredicate()</code></p>
-</li>
-<li>
-<p><code>KuduPredicate.newIsNullPredicate()</code></p>
-</li>
-</ul>
-</div>
-</li>
-<li>
-<p>The Kudu 1.3 C++ client is API- and ABI-forward-compatible with Kudu 1.2.
-Applications written and compiled against the Kudu 1.2 client library will run without
-modification against the Kudu 1.3 client library. Applications written and compiled
-against the Kudu 1.3 client library will run without modification against the Kudu 1.2
-client library unless they use one of the following new APIs:</p>
-<div class="ulist">
-<ul>
-<li>
-<p><code>kudu::DisableOpenSSLInitialization()</code></p>
-</li>
-<li>
-<p><code>KuduClientBuilder::import_authentication_credentials(&#8230;&#8203;)</code></p>
-</li>
-<li>
-<p><code>KuduClient::ExportAuthenticationCredentials(&#8230;&#8203;)</code></p>
-</li>
-<li>
-<p><code>KuduClient::NewIsNotNullPredicate(&#8230;&#8203;)</code></p>
-</li>
-<li>
-<p><code>KuduClient::NewIsNullPredicate(&#8230;&#8203;)</code></p>
-</li>
-</ul>
-</div>
-</li>
-<li>
-<p>The Kudu 1.3 Python client is API-compatible with Kudu 1.2. Applications
-written against Kudu 1.2 will continue to run against the Kudu 1.3 client
-and vice-versa.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.2.0"><a class="link" href="#rn_1.2.0">Release notes specific to 1.2.0</a></h2>
-<div class="sectionbody">
-
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.2.0_new_features"><a class="link" href="#rn_1.2.0_new_features">New features</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>Kudu clients and servers now redact user data such as cell values
-from log messages, Java exception messages, and <code>Status</code> strings.
-User metadata such as table names, column names, and partition
-bounds are not redacted.</p>
-<div class="paragraph">
-<p>Redaction is enabled by default, but may be disabled by setting the new
-<code>log_redact_user_data</code> flag to <code>false</code>.</p>
-</div>
-</li>
-<li>
-<p>Kudu&#8217;s ability to provide consistency guarantees has been substantially
-improved:</p>
-<div class="ulist">
-<ul>
-<li>
-<p>Replicas now correctly track their "safe timestamp". This timestamp
-is the maximum timestamp at which reads are guaranteed to be
-repeatable.</p>
-</li>
-<li>
-<p>A scan created using the <code>SCAN_AT_SNAPSHOT</code> mode will now
-either wait for the requested snapshot to be "safe" at the replica
-being scanned, or be re-routed to a replica where the requested
-snapshot is "safe". This ensures that all such scans are repeatable.</p>
-</li>
-<li>
-<p>Kudu Tablet Servers now properly retain historical data when a row
-with a given primary key is inserted and deleted, followed by the
-insertion of a new row with the same key. Previous versions of Kudu
-would not retain history in such situations. This allows the server
-to return correct results for snapshot scans with a timestamp in the
-past, even in the presence of such "reinsertion" scenarios.</p>
-</li>
-<li>
-<p>The Kudu clients now automatically retain the timestamp of their latest
-successful read or write operation. Scans using the <code>READ_AT_SNAPSHOT</code> mode
-without a client-provided timestamp automatically assign a timestamp
-higher than the timestamp of their most recent write. Writes also propagate
-the timestamp, ensuring that sequences of operations with causal dependencies
-between them are assigned increasing timestamps. Together, these changes
-allow clients to achieve read-your-writes consistency, and also ensure
-that snapshot scans performed by other clients return causally-consistent
-results.</p>
-</li>
-</ul>
-</div>
-</li>
-<li>
-<p>Kudu servers now automatically limit the number of log files.
-The number of log files retained can be configured using the
-<code>max_log_files</code> flag. By default, 10 log files will be retained
-at each severity level.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="_optimizations_and_improvements_4"><a class="link" href="#_optimizations_and_improvements_4">Optimizations and improvements</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>The logging in the Java and C++ clients has been substantially quieted.
-Clients no longer log messages in normal operation unless there
-is some kind of error.</p>
-</li>
-<li>
-<p>The C++ client now includes a <code>KuduSession::SetErrorBufferSpace</code>
-API which can limit the amount of memory used to buffer
-errors from asynchronous operations.</p>
-</li>
-<li>
-<p>The Java client now fetches tablet locations from the Kudu Master
-in batches of 1000, increased from batches of 10 in prior versions.
-This can substantially improve the performance of Spark and Impala
-queries running against Kudu tables with large numbers of tablets.</p>
-</li>
-<li>
-<p>Table metadata lock contention in the Kudu Master was substantially
-reduced. This improves the performance of tablet location lookups on
-large clusters with a high degree of concurrency.</p>
-</li>
-<li>
-<p>Lock contention in the Kudu Tablet Server during high-concurrency
-write workloads was also reduced. This can reduce CPU consumption and
-improve performance when a large number of concurrent clients are writing
-to a smaller number of a servers.</p>
-</li>
-<li>
-<p>Lock contention when writing log messages has been substantially reduced.
-This source of contention could cause high tail latencies on requests,
-and when under high load could contribute to cluster instability
-such as election storms and request timeouts.</p>
-</li>
-<li>
-<p>The <code>BITSHUFFLE</code> column encoding has been optimized to use the <code>AVX2</code>
-instruction set present on processors including Intel&#174; Sandy Bridge
-and later. Scans on <code>BITSHUFFLE</code>-encoded columns are now up to 30% faster.</p>
-</li>
-<li>
-<p>The <code>kudu</code> tool now accepts hyphens as an alternative to underscores
-when specifying actions. For example, <code>kudu local-replica copy-from-remote</code>
-may be used as an alternative to <code>kudu local_replica copy_from_remote</code>.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.2.0_fixed_issues"><a class="link" href="#rn_1.2.0_fixed_issues">Fixed Issues</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1508">KUDU-1508</a>
-Fixed a long-standing issue in which running Kudu on <code>ext4</code> file systems
-could cause file system corruption.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1399">KUDU-1399</a>
-Implemented an LRU cache for open files, which prevents running out of
-file descriptors on long-lived Kudu clusters. By default, Kudu will
-limit its file descriptor usage to half of its configured <code>ulimit</code>.</p>
-</li>
-<li>
-<p><a href="http://gerrit.cloudera.org:8080/5192">Gerrit #5192</a>
-Fixed an issue which caused data corruption and crashes in the case that
-a table had a non-composite (single-column) primary key, and that column
-was specified to use <code>DICT_ENCODING</code> or <code>BITSHUFFLE</code> encodings. If a
-table with an affected schema was written in previous versions of Kudu,
-the corruption will not be automatically repaired; users are encouraged
-to re-insert such tables after upgrading to Kudu 1.2 or later.</p>
-</li>
-<li>
-<p><a href="http://gerrit.cloudera.org:8080/5541">Gerrit #5541</a>
-Fixed a bug in the Spark <code>KuduRDD</code> implementation which could cause
-rows in the result set to be silently skipped in some cases.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1551">KUDU-1551</a>
-Fixed an issue in which the tablet server would crash on restart in the
-case that it had previously crashed during the process of allocating
-a new WAL segment.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1764">KUDU-1764</a>
-Fixed an issue where Kudu servers would leak approximately 16-32MB of disk
-space for every 10GB of data written to disk. After upgrading to Kudu
-1.2 or later, any disk space leaked in previous versions will be
-automatically recovered on startup.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1750">KUDU-1750</a>
-Fixed an issue where the API to drop a range partition would drop any
-partition with a matching lower <em>or</em> upper bound, rather than any partition
-with matching lower <em>and</em> upper bound.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1766">KUDU-1766</a>
-Fixed an issue in the Java client where equality predicates which compared
-an integer column to its maximum possible value (e.g. <code>Integer.MAX_VALUE</code>)
-would return incorrect results.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1780">KUDU-1780</a>
-Fixed the <code>kudu-client</code> Java artifact to properly shade classes in the
-<code>com.google.thirdparty</code> namespace. The lack of proper shading in prior
-releases could cause conflicts with certain versions of Google Guava.</p>
-</li>
-<li>
-<p><a href="http://gerrit.cloudera.org:8080/5327">Gerrit #5327</a>
-Fixed shading issues in the <code>kudu-flume-sink</code> Java artifact. The sink
-now expects that Hadoop dependencies are provided by Flume, and properly
-shades the Kudu client&#8217;s dependencies.</p>
-</li>
-<li>
-<p>Fixed a few issues using the Python client library from Python 3.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.2.0_wire_compatibility"><a class="link" href="#rn_1.2.0_wire_compatibility">Wire Protocol compatibility</a></h2>
-<div class="sectionbody">
-<div class="paragraph">
-<p>Kudu 1.2.0 is wire-compatible with previous versions of Kudu:</p>
-</div>
-<div class="ulist">
-<ul>
-<li>
-<p>Kudu 1.2 clients may connect to servers running Kudu 1.0. If the client uses features
-that are not available on the target server, an error will be returned.</p>
-</li>
-<li>
-<p>Kudu 1.0 clients may connect to servers running Kudu 1.2 without limitations.</p>
-</li>
-<li>
-<p>Rolling upgrade between Kudu 1.1 and Kudu 1.2 servers is believed to be possible
-though has not been sufficiently tested. Users are encouraged to shut down all nodes
-in the cluster, upgrade the software, and then restart the daemons on the new version.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.2.0_incompatible_changes"><a class="link" href="#rn_1.2.0_incompatible_changes">Incompatible Changes in Kudu 1.2.0</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>The replication factor of tables is now limited to a maximum of 7. In addition,
-it is no longer allowed to create a table with an even replication factor.</p>
-</li>
-<li>
-<p>The <code>GROUP_VARINT</code> encoding is now deprecated. Kudu servers have never supported
-this encoding, and now the client-side constant has been deprecated to match the
-server&#8217;s capabilities.</p>
-</li>
-</ul>
-</div>
-<div class="sect2">
-<h3 id="_new_restrictions_on_data_schemas_and_identifiers"><a class="link" href="#_new_restrictions_on_data_schemas_and_identifiers">New Restrictions on Data, Schemas, and Identifiers</a></h3>
-<div class="paragraph">
-<p>Kudu 1.2.0 introduces several new restrictions on schemas, cell size, and identifiers:</p>
-</div>
-<div class="dlist">
-<dl>
-<dt class="hdlist1">Number of Columns</dt>
-<dd>
-<p>By default, Kudu will not permit the creation of tables with
-more than 300 columns. We recommend schema designs that use fewer columns for best
-performance.</p>
-</dd>
-<dt class="hdlist1">Size of Cells</dt>
-<dd>
-<p>No individual cell may be larger than 64KB. The cells making up a
-a composite key are limited to a total of 16KB after the internal composite-key encoding
-done by Kudu. Inserting rows not conforming to these limitations will result in errors
-being returned to the client.</p>
-</dd>
-<dt class="hdlist1">Valid Identifiers</dt>
-<dd>
-<p>Identifiers such as column and table names are now restricted to
-be valid UTF-8 strings. Additionally, a maximum length of 256 characters is enforced.</p>
-</dd>
-</dl>
-</div>
-</div>
-<div class="sect2">
-<h3 id="rn_1.2.0_client_compatibility"><a class="link" href="#rn_1.2.0_client_compatibility">Client Library Compatibility</a></h3>
-<div class="ulist">
-<ul>
-<li>
-<p>The Kudu 1.2 Java client is API- and ABI-compatible with Kudu 1.1. Applications
-written against Kudu 1.1 will compile and run against the Kudu 1.2 client and
-vice-versa.</p>
-</li>
-<li>
-<p>The Kudu 1.2 C++ client is API- and ABI-forward-compatible with Kudu 1.1.
-Applications written and compiled against the Kudu 1.1 client will run without
-modification against the Kudu 1.2 client. Applications written and compiled
-against the Kudu 1.2 client will run without modification against the Kudu 1.1
-client unless they use one of the following new APIs:</p>
-<div class="ulist">
-<ul>
-<li>
-<p><code>kudu::DisableSaslInitialization()</code></p>
-</li>
-<li>
-<p><code>KuduSession::SetErrorBufferSpace(&#8230;&#8203;)</code></p>
-</li>
-</ul>
-</div>
-</li>
-<li>
-<p>The Kudu 1.2 Python client is API-compatible with Kudu 1.1. Applications
-written against Kudu 1.1 will continue to run against the Kudu 1.2 client
-and vice-versa.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.1.0"><a class="link" href="#rn_1.1.0">Release notes specific to 1.1.0</a></h2>
-<div class="sectionbody">
-
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.1.0_new_features"><a class="link" href="#rn_1.1.0_new_features">New features</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>The Python client has been brought up to feature parity with the Java and C++ clients
-and as such the package version will be brought to 1.1 with this release (from 0.3). A
-list of the highlights can be found below.</p>
-<div class="ulist">
-<ul>
-<li>
-<p>Improved Partial Row semantics</p>
-</li>
-<li>
-<p>Range partition support</p>
-</li>
-<li>
-<p>Scan Token API</p>
-</li>
-<li>
-<p>Enhanced predicate support</p>
-</li>
-<li>
-<p>Support for all Kudu data types (including a mapping of Python&#8217;s <code>datetime.datetime</code> to
-<code>UNIXTIME_MICROS</code>)</p>
-</li>
-<li>
-<p>Alter table support</p>
-</li>
-<li>
-<p>Enabled Read at Snapshot for Scanners</p>
-</li>
-<li>
-<p>Enabled Scanner Replica Selection</p>
-</li>
-<li>
-<p>A few bug fixes for Python 3 in addition to various other improvements.</p>
-</li>
-</ul>
-</div>
-</li>
-<li>
-<p>IN LIST predicate pushdown support was added to allow optimized execution of filters which
-match on a set of column values. Support for Spark, Map Reduce and Impala queries utilizing
-IN LIST pushdown is not yet complete.</p>
-</li>
-<li>
-<p>The Java client now features client-side request tracing in order to help troubleshoot timeouts.
-Error messages are now augmented with traces that show which servers were contacted before the
-timeout occurred instead of just the last error. The traces also contain RPCs that were
-required to fulfill the client&#8217;s request, such as contacting the master to discover a tablet&#8217;s
-location. Note that the traces are not available for successful requests and are not
-programmatically queryable.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="_optimizations_and_improvements_5"><a class="link" href="#_optimizations_and_improvements_5">Optimizations and improvements</a></h2>
-<div class="sectionbody">
-<div class="ulist">
-<ul>
-<li>
-<p>Kudu now publishes JAR files for Spark 2.0 compiled with Scala 2.11 along with the
-existing Spark 1.6 JAR compiled with Scala 2.10.</p>
-</li>
-<li>
-<p>The Java client now allows configuring scanners to read from the closest replica instead of
-the known leader replica. The default remains the latter. Use the relevant <code>ReplicaSelection</code>
-enum with the scanner&#8217;s builder to change this behavior.</p>
-</li>
-<li>
-<p>Tablet servers use a new policy for retaining write-ahead log (WAL) segments.
-Previously, servers used the 'log_min_segments_to_retain' flag to prioritize
-any flushes which were retaining log segments past the configured value (default 2).
-This policy caused servers to flush in-memory data more frequently than necessary,
-limiting write performance.</p>
-<div class="paragraph">
-<p>The new policy introduces a new flag 'log_target_replay_size_mb' which
-  determines the threshold at which write-ahead log retention will prioritize flushes.
-  The new flag is considered experimental and users should not need to modify
-  its value.</p>
-</div>
-<div class="paragraph">
-<p>The improved policy has been seen to improve write performance in some use cases
-  by a factor of 2x relative to the old policy.</p>
-</div>
-</li>
-<li>
-<p>Kudu&#8217;s implementation of the Raft consensus algorithm has been improved to include
-a "pre-election" phase. This can improve the stability of tablet leader election
-in high-load scenarios, especially if each server hosts a high number of tablets.</p>
-</li>
-<li>
-<p>Tablet server start-up time has been substantially improved in the case that
-the server contains a high number of tombstoned tablet replicas.</p>
-</li>
-</ul>
-</div>
-<div class="sect2">
-<h3 id="_command_line_tools"><a class="link" href="#_command_line_tools">Command line tools</a></h3>
-<div class="ulist">
-<ul>
-<li>
-<p>The tool <code>kudu tablet leader_step_down</code> has been added to manually force a leader to step down.</p>
-</li>
-<li>
-<p>The tool <code>kudu remote_replica copy</code> has been added to manually copy a replica from
-one running tablet server to another.</p>
-</li>
-<li>
-<p>The tool <code>kudu local_replica delete</code> has been added to delete a replica of a tablet.</p>
-</li>
-<li>
-<p>The <code>kudu test loadgen</code> tool has been added to replace the obsoleted
-<code>insert-generated-rows</code> standalone binary. The new tool is enriched with
-additional functionality and can be used to run load generation tests against
-a Kudu cluster.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="_wire_protocol_compatibility"><a class="link" href="#_wire_protocol_compatibility">Wire protocol compatibility</a></h2>
-<div class="sectionbody">
-<div class="paragraph">
-<p>Kudu 1.1.0 is wire-compatible with previous versions of Kudu:</p>
-</div>
-<div class="ulist">
-<ul>
-<li>
-<p>Kudu 1.1 clients may connect to servers running Kudu 1.0. If the client uses the new
-'IN LIST' predicate type, an error will be returned.</p>
-</li>
-<li>
-<p>Kudu 1.0 clients may connect to servers running Kudu 1.1 without limitations.</p>
-</li>
-<li>
-<p>Rolling upgrade between Kudu 1.0 and Kudu 1.1 servers is believed to be possible
-though has not been sufficiently tested. Users are encouraged to shut down all nodes
-in the cluster, upgrade the software, and then restart the daemons on the new version.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.1.0_incompatible_changes"><a class="link" href="#rn_1.1.0_incompatible_changes">Incompatible changes in Kudu 1.1.0</a></h2>
-<div class="sectionbody">
-<div class="sect2">
-<h3 id="_client_apis_c_java_python"><a class="link" href="#_client_apis_c_java_python">Client APIs (C++/Java/Python)</a></h3>
-<div class="ulist">
-<ul>
-<li>
-<p>The C++ client no longer requires the
-<a href="https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dual_abi.html">old gcc5 ABI</a>.
-Which ABI is actually used depends on the compiler configuration. Some new distros
-(e.g. Ubuntu 16.04) will use the new ABI. Your application must use the same ABI as is
-used by the client library; an easy way to guarantee this is to use the same compiler
-to build both.</p>
-</li>
-<li>
-<p>The C++ client&#8217;s <code>KuduSession::CountBufferedOperations()</code> method is
-deprecated. Its behavior is inconsistent unless the session runs in the
-<code>MANUAL_FLUSH</code> mode. Instead, to get number of buffered operations, count
-invocations of the <code>KuduSession::Apply()</code> method since last
-<code>KuduSession::Flush()</code> call or, if using asynchronous flushing, since last
-invocation of the callback passed into <code>KuduSession::FlushAsync()</code>.</p>
-</li>
-<li>
-<p>The Java client&#8217;s <code>OperationResponse.getWriteTimestamp</code> method was renamed to <code>getWriteTimestampRaw</code>
-to emphasize that it doesn&#8217;t return milliseconds, unlike what its Javadoc indicated. The renamed
-method was also hidden from the public APIs and should not be used.</p>
-</li>
-<li>
-<p>The Java client&#8217;s sync API (<code>KuduClient</code>, <code>KuduSession</code>, <code>KuduScanner</code>) used to throw either
-a <code>NonRecoverableException</code> or a <code>TimeoutException</code> for a timeout, and now it&#8217;s only possible for the
-client to throw the former.</p>
-</li>
-<li>
-<p>The Java client&#8217;s handling of errors in <code>KuduSession</code> was modified so that subclasses of
-<code>KuduException</code> are converted into RowErrors instead of being thrown.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.0.1"><a class="link" href="#rn_1.0.1">Release notes specific to 1.0.1</a></h2>
-<div class="sectionbody">
-<div class="paragraph">
-<p>Apache Kudu 1.0.1 is a bug fix release, with no new features or backwards
-incompatible changes.</p>
-</div>
-<div class="sect2">
-<h3 id="rn_1.0.1_fixed_issues"><a class="link" href="#rn_1.0.1_fixed_issues">Fixed Issues</a></h3>
-<div class="ulist">
-<ul>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1681">KUDU-1681</a> Fixed a bug in
-the tablet server which could cause a crash when the DNS lookup during master
-heartbeat failed.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1660">KUDU-1660</a>: Fixed a bug
-which would cause the Kudu master and tablet server to fail to start on single
-CPU systems.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1651">KUDU-1652</a>: Fixed a bug
-that would cause the C++ client, tablet server, and Java client to crash or
-throw an exception when attempting to scan a table with a predicate which
-simplifies to <code>IS NOT NULL</code> on a non-nullable column. For instance, setting a
-<code>&#8656; 127</code> predicate on an <code>INT8</code> column could trigger this bug, since the
-predicate only filters null values.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1651">KUDU-1651</a>: Fixed a bug
-that would cause the tablet server to crash when evaluating a scan with
-predicates over a dictionary encoded column containing an entire block of null
-values.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1623">KUDU-1623</a>: Fixed a bug
-that would cause the tablet server to crash when handling UPSERT operations
-that only set values for the primary key columns.</p>
-</li>
-<li>
-<p><a href="http://gerrit.cloudera.org:8080/4488">Gerrit #4488</a> Fixed a bug in the
-Java client&#8217;s KuduException class which could cause an unexpected
-NullPointerException to be thrown when the exception did not have an
-associated message.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1090">KUDU-1090</a> Fixed a bug in
-the memory tracker which could cause a rare crash during tablet server
-startup.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_1.0.0"><a class="link" href="#rn_1.0.0">Release notes specific to 1.0.0</a></h2>
-<div class="sectionbody">
-<div class="paragraph">
-<p>After approximately a year of beta releases, Apache Kudu has reached version 1.0.
-This version number signifies that the development team feels that Kudu is stable
-enough for usage in production environments.</p>
-</div>
-<div class="paragraph">
-<p>If you are new to Kudu, check out its list of <a href="index.html">features and benefits</a>.</p>
-</div>
-<div class="sect2">
-<h3 id="rn_1.0.0_new_features"><a class="link" href="#rn_1.0.0_new_features">New features</a></h3>
-<div class="paragraph">
-<p>Kudu 1.0.0 delivers a number of new features, bug fixes, and optimizations.</p>
-</div>
-<div class="ulist">
-<ul>
-<li>
-<p>Removal of multiversion concurrency control (MVCC) history is now supported.
-This is known as tablet history GC. This allows Kudu to reclaim disk space,
-where previously Kudu would keep a full history of all changes made to a
-given table since the beginning of time. Previously, the only way to reclaim
-disk space was to drop a table.</p>
-<div class="paragraph">
-<p>Kudu will still keep historical data, and the amount of history retained is
-  controlled by setting the configuration flag <code>--tablet_history_max_age_sec</code>,
-  which defaults to 15 minutes (expressed in seconds). The timestamp
-  represented by the current time minus <code>tablet_history_max_age_sec</code> is known
-  as the ancient history mark (AHM). When a compaction or flush occurs, Kudu
-  will remove the history of changes made prior to the ancient history mark.
-  This only affects historical data; currently-visible data will not be
-  removed. A specialized maintenance manager background task to remove existing
-  "cold" historical data that is not in a row affected by the normal compaction
-  process will be added in a future release.</p>
-</div>
-</li>
-<li>
-<p>Most of Kudu&#8217;s command line tools have been consolidated under a new
-top-level <code>kudu</code> tool. This reduces the number of large binaries distributed
-with Kudu and also includes much-improved help output.</p>
-</li>
-<li>
-<p>The Kudu Flume Sink now supports processing events containing Avro-encoded
-records, using the new <code>AvroKuduOperationsProducer</code>.</p>
-</li>
-<li>
-<p>Administrative tools including <code>kudu cluster ksck</code> now support running
-against multi-master Kudu clusters.</p>
-</li>
-<li>
-<p>The output of the <code>ksck</code> tool is now colorized and much easier to read.</p>
-</li>
-<li>
-<p>The C++ client API now supports writing data in <code>AUTO_FLUSH_BACKGROUND</code> mode.
-This can provide higher throughput for ingest workloads.</p>
-</li>
-</ul>
-</div>
-</div>
-<div class="sect2">
-<h3 id="_optimizations_and_improvements_6"><a class="link" href="#_optimizations_and_improvements_6">Optimizations and improvements</a></h3>
-<div class="ulist">
-<ul>
-<li>
-<p>The performance of comparison predicates on dictionary-encoded columns has
-been substantially optimized. Users are encouraged to use dictionary encoding
-on any string or binary columns with low cardinality, especially if these
-columns will be filtered with predicates.</p>
-</li>
-<li>
-<p>The Java client is now able to prune partitions from scanners based on the
-provided predicates. For example, an equality predicate on a hash-partitioned
-column will now only access those tablets that could possibly contain matching
-data. This is expected to improve performance for the Spark integration as well
-as applications using the Java client API.</p>
-</li>
-<li>
-<p>The performance of compaction selection in the tablet server has been
-substantially improved. This can increase the efficiency of the background
-maintenance threads and improve overall throughput of heavy write workloads.</p>
-</li>
-<li>
-<p>The policy by which the tablet server retains write-ahead log (WAL) files has
-been improved so that it takes into account other replicas of the tablet.
-This should help mitigate the spurious eviction of tablet replicas on machines
-that temporarily lag behind the other replicas.</p>
-</li>
-</ul>
-</div>
-</div>
-<div class="sect2">
-<h3 id="_wire_protocol_compatibility_2"><a class="link" href="#_wire_protocol_compatibility_2">Wire protocol compatibility</a></h3>
-<div class="paragraph">
-<p>Kudu 1.0.0 maintains client-server wire-compatibility with previous releases.
-Applications using the Kudu client libraries may be upgraded either
-before, at the same time, or after the Kudu servers.</p>
-</div>
-<div class="paragraph">
-<p>Kudu 1.0.0 does <em>not</em> maintain server-server wire compatibility with previous
-releases. Therefore, rolling upgrades between earlier versions of Kudu and
-Kudu 1.0.0 are not supported.</p>
-</div>
-</div>
-<div class="sect2">
-<h3 id="rn_1.0.0_incompatible_changes"><a class="link" href="#rn_1.0.0_incompatible_changes">Incompatible changes in Kudu 1.0.0</a></h3>
-<div class="sect3">
-<h4 id="_command_line_tools_2"><a class="link" href="#_command_line_tools_2">Command line tools</a></h4>
-<div class="ulist">
-<ul>
-<li>
-<p>The <code>kudu-pbc-dump</code> tool has been removed. The same functionality is now
-implemented as <code>kudu pbc dump</code>.</p>
-</li>
-<li>
-<p>The <code>kudu-ksck</code> tool has been removed. The same functionality is now
-implemented as <code>kudu cluster ksck</code>.</p>
-</li>
-<li>
-<p>The <code>cfile-dump</code> tool has been removed. The same functionality is now
-implemented as <code>kudu fs cfile dump</code>.</p>
-</li>
-<li>
-<p>The <code>log-dump</code> tool has been removed. The same functionality is now
-implemented as <code>kudu wal dump</code> and <code>kudu local_replica dump wals</code>.</p>
-</li>
-<li>
-<p>The <code>kudu-admin</code> tool has been removed. The same functionality is now
-implemented within <code>kudu table</code> and <code>kudu tablet</code>.</p>
-</li>
-<li>
-<p>The <code>kudu-fs_dump</code> tool has been removed. The same functionality is now
-implemented as <code>kudu fs dump</code>.</p>
-</li>
-<li>
-<p>The <code>kudu-ts-cli</code> tool has been removed. The same functionality is now
-implemented within <code>kudu master</code>, <code>kudu remote_replica</code>, and <code>kudu tserver</code>.</p>
-</li>
-<li>
-<p>The <code>kudu-fs_list</code> tool has been removed and some similar useful
-functionality has been moved under 'kudu local_replica'.</p>
-</li>
-</ul>
-</div>
-</div>
-<div class="sect3">
-<h4 id="_configuration_flags"><a class="link" href="#_configuration_flags">Configuration flags</a></h4>
-<div class="ulist">
-<ul>
-<li>
-<p>Some configuration flags are now marked as 'unsafe' and 'experimental'. Such flags
-are disallowed by default. Users may access these flags by enabling the additional
-flags <code>--unlock_unsafe_flags</code> and <code>--unlock_experimental_flags</code>. Usage of such flags
-is not recommended, as the flags may be removed or modified with no deprecation period
-and without notice in future Kudu releases.</p>
-</li>
-</ul>
-</div>
-</div>
-<div class="sect3">
-<h4 id="_client_apis_c_java_python_2"><a class="link" href="#_client_apis_c_java_python_2">Client APIs (C++/Java/Python)</a></h4>
-<div class="ulist">
-<ul>
-<li>
-<p>The <code>TIMESTAMP</code> column type has been renamed to <code>UNIXTIME_MICROS</code> in order to
-reduce confusion between Kudu&#8217;s timestamp support and the timestamps supported
-by other systems such as Apache Hive and Apache Impala (incubating). Existing
-tables will automatically be updated to use the new name for the type.</p>
-<div class="paragraph">
-<p>Clients upgrading to the new client libraries must move to the new name for
-  the type.  Clients using old client libraries will continue to operate using
-  the old type name, even when connected to clusters that have been
-  upgraded. Similarly, if clients are upgraded before servers, existing
-  timestamp columns will be available using the new type name.</p>
-</div>
-</li>
-<li>
-<p><code>KuduSession</code> methods in the C++ library are no longer advertised as thread-safe
-to have one set of semantics for both C++ and Java Kudu client libraries.</p>
-</li>
-<li>
-<p>The <code>KuduScanToken::TabletServers</code> method in the C++ library has been removed.
-The same information can now be found in the KuduScanToken::tablet method.</p>
-</li>
-</ul>
-</div>
-</div>
-<div class="sect3">
-<h4 id="_apache_flume_integration"><a class="link" href="#_apache_flume_integration">Apache Flume Integration</a></h4>
-<div class="ulist">
-<ul>
-<li>
-<p>The <code>KuduEventProducer</code> interface used to process Flume events into Kudu operations
-for the Kudu Flume Sink has changed, and has been renamed <code>KuduOperationsProducer</code>.
-The existing `KuduEventProducer`s have been updated for the new interface, and have
-been renamed similarly.</p>
-</li>
-</ul>
-</div>
-</div>
-</div>
-</div>
-</div>
-<div class="sect1">
-<h2 id="rn_0.10.0"><a class="link" href="#rn_0.10.0">Release notes specific to 0.10.0</a></h2>
-<div class="sectionbody">
-<div class="paragraph">
-<p>Kudu 0.10.0 delivers a number of new features, bug fixes, and optimizations,
-detailed below.</p>
-</div>
-<div class="paragraph">
-<p>Kudu 0.10.0 maintains wire-compatibility with previous releases, meaning
-that applications using the Kudu client libraries may be upgraded either
-before, at the same time, or after the Kudu servers. However, if you begin
-using new features of Kudu 0.10.0 such as manually range-partitioned tables,
-you must first upgrade all clients to this release.</p>
-</div>
-<div class="paragraph">
-<p>This release does not maintain full Java API or ABI compatibility with
-Kudu 0.9.x due to a package rename and some other small changes. See below for details.</p>
-</div>
-<div class="paragraph">
-<p>See also <a href="https://issues.apache.org/jira/issues/?jql=project%20%3D%20KUDU%20AND%20status%20%3D%20Resolved
-%20AND%20fixVersion%20%3D%200.10.0">JIRAs resolved
-for Kudu 0.10.0</a> and <a href="https://github.com/apache/kudu/compare/0.9.1...0.10.0">Git
-changes between 0.9.1 and 0.10.0</a>.</p>
-</div>
-<div class="paragraph">
-<p>To upgrade to Kudu 0.10.0, see <a href="#rn_0.10.0_upgrade">[rn_0.10.0_upgrade]</a>.</p>
-</div>
-<div class="sect2">
-<h3 id="rn_0.10.0_incompatible_changes"><a class="link" href="#rn_0.10.0_incompatible_changes">Incompatible changes and deprecated APIs in 0.10.0</a></h3>
-<div class="ulist">
-<ul>
-<li>
-<p><a href="http://gerrit.cloudera.org:8080/3737">Gerrit #3737</a> The Java client has been repackaged
-under <code>org.apache.kudu</code> instead of <code>org.kududb</code>. Import statements for Kudu classes must
-be modified in order to compile against 0.10.0. Wire compatibility is maintained.</p>
-</li>
-<li>
-<p><a href="https://gerrit.cloudera.org/#/c/3055/">Gerrit #3055</a> The Java client&#8217;s
-synchronous API methods now throw <code>KuduException</code> instead of <code>Exception</code>.
-Existing code that catches <code>Exception</code> should still compile, but introspection of an
-exception&#8217;s message may be impacted. This change was made to allow thrown exceptions to be
-queried more easily using <code>KuduException.getStatus</code> and calling one of <code>Status&#8217;s methods.
-For example, an operation that tries to delete a table that doesn&#8217;t exist would return a
-`Status</code> that returns true when queried on <code>isNotFound()</code>.</p>
-</li>
-<li>
-<p>The Java client&#8217;s <code>KuduTable.getTabletsLocations</code> set of methods is now
-deprecated. Additionally, they now take an exclusive end partition key instead
-of an inclusive key. Applications are encouraged to use the scan tokens API
-instead of these methods in the future.</p>
-</li>
-<li>
-<p>The C++ API for specifying split points on range-partitioned tables has been improved
-to make it easier for callers to properly manage the ownership of the provided rows.</p>
-<div class="paragraph">
-<p>The <code>TableCreator::split_rows</code> API took a <code>vector&lt;const KuduPartialRow*&gt;</code>, which
-  made it very difficult for the calling application to do proper error handling with
-  cleanup when setting the fields of the <code>KuduPartialRow</code>. This API has been now been
-  deprecated and replaced by a new method <code>TableCreator::add_range_split</code> which allows
-  easier use of smart pointers for safe memory management.</p>
-</div>
-</li>
-<li>
-<p>The Java client&#8217;s internal buffering has been reworked. Previously, the number of
-buffered write operations was constrained on a per-tablet-server basis. Now, the configured
-maximum buffer size constrains the total number of buffered operations across all
-tablet servers in the cluster. This provides a more consistent bound on the memory
-usage of the client regardless of the size of the cluster to which it is writing.</p>
-<div class="paragraph">
-<p>This change can negatively affect the write performance of Java clients which rely on
-  buffered writes. Consider using the <code>setMutationBufferSpace</code> API to increase a
-  session&#8217;s maximum buffer size if write performance seems to be degraded after upgrading
-  to Kudu 0.10.0.</p>
-</div>
-</li>
-<li>
-<p>The "remote bootstrap" process used to copy a tablet replica from one host to
-another has been renamed to "Tablet Copy". This resulted in the renaming of
-several RPC metrics. Any users previously explicitly fetching or monitoring metrics
-related to Remote Bootstrap should update their scripts to reflect the new names.</p>
-</li>
-<li>
-<p>The SparkSQL datasource for Kudu no longer supports mode <code>Overwrite</code>. Users should
-use the new <code>KuduContext.upsertRows</code> method instead. Additionally, inserts using the
-datasource are now upserts by default. The older behavior can be restored by setting
-the <code>operation</code> parameter to <code>insert</code>.</p>
-</li>
-</ul>
-</div>
-</div>
-<div class="sect2">
-<h3 id="rn_0.10.0_new_features"><a class="link" href="#rn_0.10.0_new_features">New features</a></h3>
-<div class="ulist">
-<ul>
-<li>
-<p>Users may now manually manage the partitioning of a range-partitioned table.
-When a table is created, the user may specify a set of range partitions that
-do not cover the entire available key space. A user may add or drop range
-partitions to existing tables.</p>
-<div class="paragraph">
-<p>This feature can be particularly helpful with time series workloads in which
-  new partitions can be created on an hourly or daily basis. Old partitions
-  may be efficiently dropped if the application does not need to retain historical
-  data past a certain point.</p>
-</div>
-<div class="paragraph">
-<p>This feature is considered experimental for the 0.10 release. More details of
-  the new feature can be found in the accompanying
-  <a href="https://kudu.apache.org/2016/08/23/new-range-partitioning-features.html">blog post</a>.</p>
-</div>
-</li>
-<li>
-<p>Support for running Kudu clusters with multiple masters has been stabilized.
-Users may start a cluster with three or five masters to provide fault tolerance
-despite a failure of one or two masters, respectively.</p>
-<div class="paragraph">
-<p>Note that certain tools (e.g. <code>ksck</code>) are still lacking complete support for
-  multiple masters. These deficiencies will be addressed in a following release.</p>
-</div>
-</li>
-<li>
-<p>Kudu now supports the ability to reserve a certain amount of free disk space
-in each of its configured data directories. If a directory&#8217;s free disk space
-drops to less than the configured minimum, Kudu will stop writing to that
-directory until space becomes available. If no space is available in any
-configured directory, Kudu will abort.</p>
-<div class="paragraph">
-<p>This feature may be configured using the <code>fs_data_dirs_reserved_bytes</code> and
-  <code>fs_wal_dir_reserved_bytes</code> flags.</p>
-</div>
-</li>
-<li>
-<p>The Spark integration&#8217;s <code>KuduContext</code> now supports four new methods for writing to
-Kudu tables: <code>insertRows</code>, <code>upsertRows</code>, <code>updateRows</code>, and <code>deleteRows</code>. These are
-now the preferred way to write to Kudu tables from Spark.</p>
-</li>
-</ul>
-</div>
-</div>
-<div class="sect2">
-<h3 id="rn_0.10.0_improvements"><a class="link" href="#rn_0.10.0_improvements">Improvements and optimizations</a></h3>
-<div class="ulist">
-<ul>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1516">KUDU-1516</a> The <code>kudu-ksck</code> tool
-has been improved and now detects problems such as when a tablet does not have
-a majority of replicas on live tablet servers, or if those replicas aren’t in a
-good state. Users who currently depend on the tool to detect inconsistencies may now see
-failures when before they wouldn&#8217;t see any.</p>
-</li>
-<li>
-<p><a href="https://gerrit.cloudera.org:8080/3477">Gerrit #3477</a> The way operations are buffered in
-the Java client has been reworked. Previously, the session&#8217;s buffer size was set per tablet, meaning that a buffer
-size of 1,000 for 10 tablets being written to allowed for 10,000 operations to be buffered at the
-same time. With this change, all the tablets share one buffer, so users might need to set a
-bigger buffer size in order to reach the same level of performance as before.</p>
-</li>
-<li>
-<p><a href="https://gerrit.cloudera.org/#/c/3674/">Gerrit #3674</a> Added LESS and GREATER options for
-column predicates.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1444">KUDU-1444</a> added support for passing
-back basic per-scan metrics (e.g cache hit rate) from the server to the C++ client. See the
-<code>KuduScanner::GetResourceMetrics()</code> API for detailed usage. This feature will be supported
-in the Java client API in a future release.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1446">KUDU-1446</a> improved the order in
-which the tablet server evaluates predicates, so that predicates on smaller columns
-are evaluated first. This may improve performance on queries which apply predicates
-on multiple columns of different sizes.</p>
-</li>
-<li>
-<p><a href="https://issues.apache.org/jira/browse/KUDU-1398">KUDU-1398</a> improved the storage
-efficiency of Kudu&#8217;s internal primary key indexes. This optimization should decrease space
-usage and improve random access performance, particularly for workloads with lengthy
-primary keys.</p>
-</li>
-</ul>
-</div>
-</div>
-<div class="sect2">
-<h3 id="rn_0.10.0_fixed_issues"><a class="link" href="#rn_0.10.0_fixed_issues">Fixed Issues</a></h3>
-<div class="ulist">
-<ul>
-<li>
-<p><a href="https://gerrit.cloudera.org/#/c/3541/">Ge

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