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From jbap...@apache.org
Subject [42/51] [partial] incubator-impala git commit: IMPALA-4181 [DOCS] Publish rendered Impala documentation to ASF site
Date Wed, 12 Apr 2017 18:25:46 GMT
http://git-wip-us.apache.org/repos/asf/incubator-impala/blob/75c46918/docs/build/html/topics/impala_components.html
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+<!DOCTYPE html
+  SYSTEM "about:legacy-compat">
+<html lang="en"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><meta charset="UTF-8"><meta name="copyright" content="(C) Copyright 2017"><meta name="DC.rights.owner" content="(C) Copyright 2017"><meta name="DC.Type" content="concept"><meta name="DC.Relation" scheme="URI" content="../topics/impala_concepts.html"><meta name="prodname" content="Impala"><meta name="prodname" content="Impala"><meta name="prodname" content="Impala"><meta name="prodname" content="Impala"><meta name="prodname" content="Impala"><meta name="version" content="Impala 2.8.x"><meta name="version" content="Impala 2.8.x"><meta name="version" content="Impala 2.8.x"><meta name="version" content="Impala 2.8.x"><meta name="version" content="Impala 2.8.x"><meta name="DC.Format" content="XHTML"><meta name="DC.Identifier" content="intro_components"><link rel="stylesheet" type="text/css" href="../commonltr.css"><title>Components of the Impala Server</title></head><body id="intro_components"><main 
 role="main"><article role="article" aria-labelledby="ariaid-title1">
+
+  <h1 class="title topictitle1" id="ariaid-title1">Components of the Impala Server</h1>
+  
+  
+
+  <div class="body conbody">
+
+    <p class="p">
+      The Impala server is a distributed, massively parallel processing (MPP) database engine. It consists of
+      different daemon processes that run on specific hosts within your <span class="keyword"></span> cluster.
+    </p>
+
+    <p class="p toc inpage"></p>
+  </div>
+
+  <nav role="navigation" class="related-links"><div class="familylinks"><div class="parentlink"><strong>Parent topic:</strong> <a class="link" href="../topics/impala_concepts.html">Impala Concepts and Architecture</a></div></div></nav><article class="topic concept nested1" aria-labelledby="ariaid-title2" id="intro_components__intro_impalad">
+
+    <h2 class="title topictitle2" id="ariaid-title2">The Impala Daemon</h2>
+
+    <div class="body conbody">
+
+      <p class="p">
+        The core Impala component is a daemon process that runs on each DataNode of the cluster, physically represented
+        by the <code class="ph codeph">impalad</code> process. It reads and writes to data files; accepts queries transmitted
+        from the <code class="ph codeph">impala-shell</code> command, Hue, JDBC, or ODBC; parallelizes the queries and
+        distributes work across the cluster; and transmits intermediate query results back to the
+        central coordinator node.
+      </p>
+
+      <p class="p">
+        You can submit a query to the Impala daemon running on any DataNode, and that instance of the daemon serves as the
+        <dfn class="term">coordinator node</dfn> for that query. The other nodes transmit partial results back to the
+        coordinator, which constructs the final result set for a query. When running experiments with functionality
+        through the <code class="ph codeph">impala-shell</code> command, you might always connect to the same Impala daemon for
+        convenience. For clusters running production workloads, you might load-balance by
+        submitting each query to a different Impala daemon in round-robin style, using the JDBC or ODBC interfaces.
+      </p>
+
+      <p class="p">
+        The Impala daemons are in constant communication with the <dfn class="term">statestore</dfn>, to confirm which nodes
+        are healthy and can accept new work.
+      </p>
+
+      <p class="p">
+        They also receive broadcast messages from the <span class="keyword cmdname">catalogd</span> daemon (introduced in Impala 1.2)
+        whenever any Impala node in the cluster creates, alters, or drops any type of object, or when an
+        <code class="ph codeph">INSERT</code> or <code class="ph codeph">LOAD DATA</code> statement is processed through Impala. This
+        background communication minimizes the need for <code class="ph codeph">REFRESH</code> or <code class="ph codeph">INVALIDATE
+        METADATA</code> statements that were needed to coordinate metadata across nodes prior to Impala 1.2.
+      </p>
+
+      <p class="p">
+        <strong class="ph b">Related information:</strong> <a class="xref" href="impala_config_options.html#config_options">Modifying Impala Startup Options</a>,
+        <a class="xref" href="impala_processes.html#processes">Starting Impala</a>, <a class="xref" href="impala_timeouts.html#impalad_timeout">Setting the Idle Query and Idle Session Timeouts for impalad</a>,
+        <a class="xref" href="impala_ports.html#ports">Ports Used by Impala</a>, <a class="xref" href="impala_proxy.html#proxy">Using Impala through a Proxy for High Availability</a>
+      </p>
+    </div>
+  </article>
+
+  <article class="topic concept nested1" aria-labelledby="ariaid-title3" id="intro_components__intro_statestore">
+
+    <h2 class="title topictitle2" id="ariaid-title3">The Impala Statestore</h2>
+
+    <div class="body conbody">
+
+      <p class="p">
+        The Impala component known as the <dfn class="term">statestore</dfn> checks on the health of Impala daemons on all the
+        DataNodes in a cluster, and continuously relays its findings to each of those daemons. It is physically
+        represented by a daemon process named <code class="ph codeph">statestored</code>; you only need such a process on one
+        host in the cluster. If an Impala daemon goes offline due to hardware failure, network error, software issue,
+        or other reason, the statestore informs all the other Impala daemons so that future queries can avoid making
+        requests to the unreachable node.
+      </p>
+
+      <p class="p">
+        Because the statestore's purpose is to help when things go wrong, it is not critical to the normal
+        operation of an Impala cluster. If the statestore is not running or becomes unreachable, the Impala daemons
+        continue running and distributing work among themselves as usual; the cluster just becomes less robust if
+        other Impala daemons fail while the statestore is offline. When the statestore comes back online, it re-establishes
+        communication with the Impala daemons and resumes its monitoring function.
+      </p>
+
+      <p class="p">
+        Most considerations for load balancing and high availability apply to the <span class="keyword cmdname">impalad</span> daemon.
+        The <span class="keyword cmdname">statestored</span> and <span class="keyword cmdname">catalogd</span> daemons do not have special
+        requirements for high availability, because problems with those daemons do not result in data loss.
+        If those daemons become unavailable due to an outage on a particular
+        host, you can stop the Impala service, delete the <span class="ph uicontrol">Impala StateStore</span> and
+        <span class="ph uicontrol">Impala Catalog Server</span> roles, add the roles on a different host, and restart the
+        Impala service.
+      </p>
+
+      <p class="p">
+        <strong class="ph b">Related information:</strong>
+      </p>
+
+      <p class="p">
+        <a class="xref" href="impala_scalability.html#statestore_scalability">Scalability Considerations for the Impala Statestore</a>,
+        <a class="xref" href="impala_config_options.html#config_options">Modifying Impala Startup Options</a>, <a class="xref" href="impala_processes.html#processes">Starting Impala</a>,
+        <a class="xref" href="impala_timeouts.html#statestore_timeout">Increasing the Statestore Timeout</a>, <a class="xref" href="impala_ports.html#ports">Ports Used by Impala</a>
+      </p>
+    </div>
+  </article>
+
+  <article class="topic concept nested1" aria-labelledby="ariaid-title4" id="intro_components__intro_catalogd">
+
+    <h2 class="title topictitle2" id="ariaid-title4">The Impala Catalog Service</h2>
+
+    <div class="body conbody">
+
+      <p class="p">
+        The Impala component known as the <dfn class="term">catalog service</dfn> relays the metadata changes from Impala SQL
+        statements to all the DataNodes in a cluster. It is physically represented by a daemon process named
+        <code class="ph codeph">catalogd</code>; you only need such a process on one host in the cluster. Because the requests
+        are passed through the statestore daemon, it makes sense to run the <span class="keyword cmdname">statestored</span> and
+        <span class="keyword cmdname">catalogd</span> services on the same host.
+      </p>
+
+      <p class="p">
+        The catalog service avoids the need to issue
+        <code class="ph codeph">REFRESH</code> and <code class="ph codeph">INVALIDATE METADATA</code> statements when the metadata changes are
+        performed by statements issued through Impala. When you create a table, load data, and so on through Hive,
+        you do need to issue <code class="ph codeph">REFRESH</code> or <code class="ph codeph">INVALIDATE METADATA</code> on an Impala node
+        before executing a query there.
+      </p>
+
+      <p class="p">
+        This feature touches a number of aspects of Impala:
+      </p>
+
+
+
+      <ul class="ul" id="intro_catalogd__catalogd_xrefs">
+        <li class="li">
+          <p class="p">
+            See <a class="xref" href="impala_install.html#install">Installing Impala</a>, <a class="xref" href="impala_upgrading.html#upgrading">Upgrading Impala</a> and
+            <a class="xref" href="impala_processes.html#processes">Starting Impala</a>, for usage information for the
+            <span class="keyword cmdname">catalogd</span> daemon.
+          </p>
+        </li>
+
+        <li class="li">
+          <p class="p">
+            The <code class="ph codeph">REFRESH</code> and <code class="ph codeph">INVALIDATE METADATA</code> statements are not needed
+            when the <code class="ph codeph">CREATE TABLE</code>, <code class="ph codeph">INSERT</code>, or other table-changing or
+            data-changing operation is performed through Impala. These statements are still needed if such
+            operations are done through Hive or by manipulating data files directly in HDFS, but in those cases the
+            statements only need to be issued on one Impala node rather than on all nodes. See
+            <a class="xref" href="impala_refresh.html#refresh">REFRESH Statement</a> and
+            <a class="xref" href="impala_invalidate_metadata.html#invalidate_metadata">INVALIDATE METADATA Statement</a> for the latest usage information for
+            those statements.
+          </p>
+        </li>
+      </ul>
+
+      <p class="p">
+        By default, the metadata loading and caching on startup happens asynchronously, so Impala can begin
+        accepting requests promptly. To enable the original behavior, where Impala waited until all metadata was
+        loaded before accepting any requests, set the <span class="keyword cmdname">catalogd</span> configuration option
+        <code class="ph codeph">--load_catalog_in_background=false</code>.
+      </p>
+
+      <p class="p">
+        Most considerations for load balancing and high availability apply to the <span class="keyword cmdname">impalad</span> daemon.
+        The <span class="keyword cmdname">statestored</span> and <span class="keyword cmdname">catalogd</span> daemons do not have special
+        requirements for high availability, because problems with those daemons do not result in data loss.
+        If those daemons become unavailable due to an outage on a particular
+        host, you can stop the Impala service, delete the <span class="ph uicontrol">Impala StateStore</span> and
+        <span class="ph uicontrol">Impala Catalog Server</span> roles, add the roles on a different host, and restart the
+        Impala service.
+      </p>
+
+      <div class="note note note_note"><span class="note__title notetitle">Note:</span> 
+        <p class="p">
+        In Impala 1.2.4 and higher, you can specify a table name with <code class="ph codeph">INVALIDATE METADATA</code> after
+        the table is created in Hive, allowing you to make individual tables visible to Impala without doing a full
+        reload of the catalog metadata. Impala 1.2.4 also includes other changes to make the metadata broadcast
+        mechanism faster and more responsive, especially during Impala startup. See
+        <a class="xref" href="../shared/../topics/impala_new_features.html#new_features_124">New Features in Impala 1.2.4</a> for details.
+      </p>
+      </div>
+
+      <p class="p">
+        <strong class="ph b">Related information:</strong> <a class="xref" href="impala_config_options.html#config_options">Modifying Impala Startup Options</a>,
+        <a class="xref" href="impala_processes.html#processes">Starting Impala</a>, <a class="xref" href="impala_ports.html#ports">Ports Used by Impala</a>
+      </p>
+    </div>
+  </article>
+</article></main></body></html>
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+<!DOCTYPE html
+  SYSTEM "about:legacy-compat">
+<html lang="en"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><meta charset="UTF-8"><meta name="copyright" content="(C) Copyright 2017"><meta name="DC.rights.owner" content="(C) Copyright 2017"><meta name="DC.Type" content="concept"><meta name="DC.Relation" scheme="URI" content="../topics/impala_query_options.html"><meta name="prodname" content="Impala"><meta name="prodname" content="Impala"><meta name="version" content="Impala 2.8.x"><meta name="version" content="Impala 2.8.x"><meta name="DC.Format" content="XHTML"><meta name="DC.Identifier" content="compression_codec"><link rel="stylesheet" type="text/css" href="../commonltr.css"><title>COMPRESSION_CODEC Query Option (Impala 2.0 or higher only)</title></head><body id="compression_codec"><main role="main"><article role="article" aria-labelledby="ariaid-title1">
+
+  <h1 class="title topictitle1" id="ariaid-title1">COMPRESSION_CODEC Query Option (<span class="keyword">Impala 2.0</span> or higher only)</h1>
+  
+  
+
+  <div class="body conbody">
+
+
+
+
+
+    <p class="p">
+      
+      When Impala writes Parquet data files using the <code class="ph codeph">INSERT</code> statement, the underlying compression
+      is controlled by the <code class="ph codeph">COMPRESSION_CODEC</code> query option.
+    </p>
+
+    <div class="note note note_note"><span class="note__title notetitle">Note:</span> 
+      Prior to Impala 2.0, this option was named <code class="ph codeph">PARQUET_COMPRESSION_CODEC</code>. In Impala 2.0 and
+      later, the <code class="ph codeph">PARQUET_COMPRESSION_CODEC</code> name is not recognized. Use the more general name
+      <code class="ph codeph">COMPRESSION_CODEC</code> for new code.
+    </div>
+
+    <p class="p">
+        <strong class="ph b">Syntax:</strong>
+      </p>
+
+<pre class="pre codeblock"><code>SET COMPRESSION_CODEC=<var class="keyword varname">codec_name</var>;</code></pre>
+
+    <p class="p">
+      The allowed values for this query option are <code class="ph codeph">SNAPPY</code> (the default), <code class="ph codeph">GZIP</code>,
+      and <code class="ph codeph">NONE</code>.
+    </p>
+
+    <div class="note note note_note"><span class="note__title notetitle">Note:</span> 
+      A Parquet file created with <code class="ph codeph">COMPRESSION_CODEC=NONE</code> is still typically smaller than the
+      original data, due to encoding schemes such as run-length encoding and dictionary encoding that are applied
+      separately from compression.
+    </div>
+
+    <p class="p"></p>
+
+    <p class="p">
+      The option value is not case-sensitive.
+    </p>
+
+    <p class="p">
+      If the option is set to an unrecognized value, all kinds of queries will fail due to the invalid option
+      setting, not just queries involving Parquet tables. (The value <code class="ph codeph">BZIP2</code> is also recognized, but
+      is not compatible with Parquet tables.)
+    </p>
+
+    <p class="p">
+      <strong class="ph b">Type:</strong> <code class="ph codeph">STRING</code>
+    </p>
+
+    <p class="p">
+      <strong class="ph b">Default:</strong> <code class="ph codeph">SNAPPY</code>
+    </p>
+
+
+    <p class="p">
+        <strong class="ph b">Examples:</strong>
+      </p>
+
+<pre class="pre codeblock"><code>set compression_codec=gzip;
+insert into parquet_table_highly_compressed select * from t1;
+
+set compression_codec=snappy;
+insert into parquet_table_compression_plus_fast_queries select * from t1;
+
+set compression_codec=none;
+insert into parquet_table_no_compression select * from t1;
+
+set compression_codec=foo;
+select * from t1 limit 5;
+ERROR: Invalid compression codec: foo
+</code></pre>
+
+    <p class="p">
+        <strong class="ph b">Related information:</strong>
+      </p>
+
+    <p class="p">
+      For information about how compressing Parquet data files affects query performance, see
+      <a class="xref" href="impala_parquet.html#parquet_compression">Snappy and GZip Compression for Parquet Data Files</a>.
+    </p>
+  </div>
+<nav role="navigation" class="related-links"><div class="familylinks"><div class="parentlink"><strong>Parent topic:</strong> <a class="link" href="../topics/impala_query_options.html">Query Options for the SET Statement</a></div></div></nav></article></main></body></html>
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+<!DOCTYPE html
+  SYSTEM "about:legacy-compat">
+<html lang="en"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><meta charset="UTF-8"><meta name="copyright" content="(C) Copyright 2017"><meta name="DC.rights.owner" content="(C) Copyright 2017"><meta name="DC.Type" content="concept"><meta name="DC.Relation" scheme="URI" content="../topics/impala_langref_sql.html"><meta name="prodname" content="Impala"><meta name="prodname" content="Impala"><meta name="version" content="Impala 2.8.x"><meta name="version" content="Impala 2.8.x"><meta name="DC.Format" content="XHTML"><meta name="DC.Identifier" content="compute_stats"><link rel="stylesheet" type="text/css" href="../commonltr.css"><title>COMPUTE STATS Statement</title></head><body id="compute_stats"><main role="main"><article role="article" aria-labelledby="ariaid-title1">
+
+  <h1 class="title topictitle1" id="ariaid-title1">COMPUTE STATS Statement</h1>
+  
+  
+
+  <div class="body conbody">
+
+    <p class="p">
+      
+      Gathers information about volume and distribution of data in a table and all associated columns and
+      partitions. The information is stored in the metastore database, and used by Impala to help optimize queries.
+      For example, if Impala can determine that a table is large or small, or has many or few distinct values it
+      can organize parallelize the work appropriately for a join query or insert operation. For details about the
+      kinds of information gathered by this statement, see <a class="xref" href="impala_perf_stats.html#perf_stats">Table and Column Statistics</a>.
+    </p>
+
+    <p class="p">
+        <strong class="ph b">Syntax:</strong>
+      </p>
+
+<pre class="pre codeblock"><code>COMPUTE STATS [<var class="keyword varname">db_name</var>.]<var class="keyword varname">table_name</var>
+COMPUTE INCREMENTAL STATS [<var class="keyword varname">db_name</var>.]<var class="keyword varname">table_name</var> [PARTITION (<var class="keyword varname">partition_spec</var>)]
+
+<var class="keyword varname">partition_spec</var> ::= <var class="keyword varname">simple_partition_spec</var> | <span class="ph"><var class="keyword varname">complex_partition_spec</var></span>
+
+<var class="keyword varname">simple_partition_spec</var> ::= <var class="keyword varname">partition_col</var>=<var class="keyword varname">constant_value</var>
+
+<span class="ph"><var class="keyword varname">complex_partition_spec</var> ::= <var class="keyword varname">comparison_expression_on_partition_col</var></span>
+</code></pre>
+
+    <p class="p">
+        The <code class="ph codeph">PARTITION</code> clause is only allowed in combination with the <code class="ph codeph">INCREMENTAL</code>
+        clause. It is optional for <code class="ph codeph">COMPUTE INCREMENTAL STATS</code>, and required for <code class="ph codeph">DROP
+        INCREMENTAL STATS</code>. Whenever you specify partitions through the <code class="ph codeph">PARTITION
+        (<var class="keyword varname">partition_spec</var>)</code> clause in a <code class="ph codeph">COMPUTE INCREMENTAL STATS</code> or
+        <code class="ph codeph">DROP INCREMENTAL STATS</code> statement, you must include all the partitioning columns in the
+        specification, and specify constant values for all the partition key columns.
+      </p>
+
+    <p class="p">
+        <strong class="ph b">Usage notes:</strong>
+      </p>
+
+    <p class="p">
+      Originally, Impala relied on users to run the Hive <code class="ph codeph">ANALYZE TABLE</code> statement, but that method
+      of gathering statistics proved unreliable and difficult to use. The Impala <code class="ph codeph">COMPUTE STATS</code>
+      statement is built from the ground up to improve the reliability and user-friendliness of this operation.
+      <code class="ph codeph">COMPUTE STATS</code> does not require any setup steps or special configuration. You only run a
+      single Impala <code class="ph codeph">COMPUTE STATS</code> statement to gather both table and column statistics, rather
+      than separate Hive <code class="ph codeph">ANALYZE TABLE</code> statements for each kind of statistics.
+    </p>
+
+    <p class="p">
+      The <code class="ph codeph">COMPUTE INCREMENTAL STATS</code> variation is a shortcut for partitioned tables that works on a
+      subset of partitions rather than the entire table. The incremental nature makes it suitable for large tables
+      with many partitions, where a full <code class="ph codeph">COMPUTE STATS</code> operation takes too long to be practical
+      each time a partition is added or dropped. See <a class="xref" href="impala_perf_stats.html#perf_stats_incremental">Overview of Incremental Statistics</a>
+      for full usage details.
+    </p>
+
+    <p class="p">
+      <code class="ph codeph">COMPUTE INCREMENTAL STATS</code> only applies to partitioned tables. If you use the
+      <code class="ph codeph">INCREMENTAL</code> clause for an unpartitioned table, Impala automatically uses the original
+      <code class="ph codeph">COMPUTE STATS</code> statement. Such tables display <code class="ph codeph">false</code> under the
+      <code class="ph codeph">Incremental stats</code> column of the <code class="ph codeph">SHOW TABLE STATS</code> output.
+    </p>
+
+    <div class="note note note_note"><span class="note__title notetitle">Note:</span> 
+      Because many of the most performance-critical and resource-intensive operations rely on table and column
+      statistics to construct accurate and efficient plans, <code class="ph codeph">COMPUTE STATS</code> is an important step at
+      the end of your ETL process. Run <code class="ph codeph">COMPUTE STATS</code> on all tables as your first step during
+      performance tuning for slow queries, or troubleshooting for out-of-memory conditions:
+      <ul class="ul">
+        <li class="li">
+          Accurate statistics help Impala construct an efficient query plan for join queries, improving performance
+          and reducing memory usage.
+        </li>
+
+        <li class="li">
+          Accurate statistics help Impala distribute the work effectively for insert operations into Parquet
+          tables, improving performance and reducing memory usage.
+        </li>
+
+        <li class="li">
+          Accurate statistics help Impala estimate the memory required for each query, which is important when you
+          use resource management features, such as admission control and the YARN resource management framework.
+          The statistics help Impala to achieve high concurrency, full utilization of available memory, and avoid
+          contention with workloads from other Hadoop components.
+        </li>
+        <li class="li">
+          In <span class="keyword">Impala 2.8</span> and higher, when you run the
+          <code class="ph codeph">COMPUTE STATS</code> or <code class="ph codeph">COMPUTE INCREMENTAL STATS</code>
+          statement against a Parquet table, Impala automatically applies the query
+          option setting <code class="ph codeph">MT_DOP=4</code> to increase the amount of intra-node
+          parallelism during this CPU-intensive operation. See <a class="xref" href="impala_mt_dop.html">MT_DOP Query Option</a>
+          for details about what this query option does and how to use it with
+          CPU-intensive <code class="ph codeph">SELECT</code> statements.
+        </li>
+      </ul>
+    </div>
+
+    <p class="p">
+      <strong class="ph b">Computing stats for groups of partitions:</strong>
+    </p>
+
+    <p class="p">
+      In <span class="keyword">Impala 2.8</span> and higher, you can run <code class="ph codeph">COMPUTE INCREMENTAL STATS</code>
+      on multiple partitions, instead of the entire table or one partition at a time. You include
+      comparison operators other than <code class="ph codeph">=</code> in the <code class="ph codeph">PARTITION</code> clause,
+      and the <code class="ph codeph">COMPUTE INCREMENTAL STATS</code> statement applies to all partitions that
+      match the comparison expression.
+    </p>
+
+    <p class="p">
+      For example, the <code class="ph codeph">INT_PARTITIONS</code> table contains 4 partitions.
+      The following <code class="ph codeph">COMPUTE INCREMENTAL STATS</code> statements affect some but not all
+      partitions, as indicated by the <code class="ph codeph">Updated <var class="keyword varname">n</var> partition(s)</code>
+      messages. The partitions that are affected depend on values in the partition key column <code class="ph codeph">X</code>
+      that match the comparison expression in the <code class="ph codeph">PARTITION</code> clause.
+    </p>
+
+<pre class="pre codeblock"><code>
+show partitions int_partitions;
++-------+-------+--------+------+--------------+-------------------+---------+...
+| x     | #Rows | #Files | Size | Bytes Cached | Cache Replication | Format  |...
++-------+-------+--------+------+--------------+-------------------+---------+...
+| 99    | -1    | 0      | 0B   | NOT CACHED   | NOT CACHED        | PARQUET |...
+| 120   | -1    | 0      | 0B   | NOT CACHED   | NOT CACHED        | TEXT    |...
+| 150   | -1    | 0      | 0B   | NOT CACHED   | NOT CACHED        | TEXT    |...
+| 200   | -1    | 0      | 0B   | NOT CACHED   | NOT CACHED        | TEXT    |...
+| Total | -1    | 0      | 0B   | 0B           |                   |         |...
++-------+-------+--------+------+--------------+-------------------+---------+...
+
+compute incremental stats int_partitions partition (x &lt; 100);
++-----------------------------------------+
+| summary                                 |
++-----------------------------------------+
+| Updated 1 partition(s) and 1 column(s). |
++-----------------------------------------+
+
+compute incremental stats int_partitions partition (x in (100, 150, 200));
++-----------------------------------------+
+| summary                                 |
++-----------------------------------------+
+| Updated 2 partition(s) and 1 column(s). |
++-----------------------------------------+
+
+compute incremental stats int_partitions partition (x between 100 and 175);
++-----------------------------------------+
+| summary                                 |
++-----------------------------------------+
+| Updated 2 partition(s) and 1 column(s). |
++-----------------------------------------+
+
+compute incremental stats int_partitions partition (x in (100, 150, 200) or x &lt; 100);
++-----------------------------------------+
+| summary                                 |
++-----------------------------------------+
+| Updated 3 partition(s) and 1 column(s). |
++-----------------------------------------+
+
+compute incremental stats int_partitions partition (x != 150);
++-----------------------------------------+
+| summary                                 |
++-----------------------------------------+
+| Updated 3 partition(s) and 1 column(s). |
++-----------------------------------------+
+
+</code></pre>
+
+    <p class="p">
+        <strong class="ph b">Complex type considerations:</strong>
+      </p>
+
+    <p class="p">
+      Currently, the statistics created by the <code class="ph codeph">COMPUTE STATS</code> statement do not include
+      information about complex type columns. The column stats metrics for complex columns are always shown
+      as -1. For queries involving complex type columns, Impala uses
+      heuristics to estimate the data distribution within such columns.
+    </p>
+
+    <p class="p">
+        <strong class="ph b">HBase considerations:</strong>
+      </p>
+
+    <p class="p">
+      <code class="ph codeph">COMPUTE STATS</code> works for HBase tables also. The statistics gathered for HBase tables are
+      somewhat different than for HDFS-backed tables, but that metadata is still used for optimization when HBase
+      tables are involved in join queries.
+    </p>
+
+    <p class="p">
+        <strong class="ph b">Amazon S3 considerations:</strong>
+      </p>
+
+    <p class="p">
+      <code class="ph codeph">COMPUTE STATS</code> also works for tables where data resides in the Amazon Simple Storage Service (S3).
+      See <a class="xref" href="impala_s3.html#s3">Using Impala with the Amazon S3 Filesystem</a> for details.
+    </p>
+
+    <p class="p">
+        <strong class="ph b">Performance considerations:</strong>
+      </p>
+
+    <p class="p">
+      The statistics collected by <code class="ph codeph">COMPUTE STATS</code> are used to optimize join queries
+      <code class="ph codeph">INSERT</code> operations into Parquet tables, and other resource-intensive kinds of SQL statements.
+      See <a class="xref" href="impala_perf_stats.html#perf_stats">Table and Column Statistics</a> for details.
+    </p>
+
+    <p class="p">
+      For large tables, the <code class="ph codeph">COMPUTE STATS</code> statement itself might take a long time and you
+      might need to tune its performance. The <code class="ph codeph">COMPUTE STATS</code> statement does not work with the
+      <code class="ph codeph">EXPLAIN</code> statement, or the <code class="ph codeph">SUMMARY</code> command in <span class="keyword cmdname">impala-shell</span>.
+      You can use the <code class="ph codeph">PROFILE</code> statement in <span class="keyword cmdname">impala-shell</span> to examine timing information
+      for the statement as a whole. If a basic <code class="ph codeph">COMPUTE STATS</code> statement takes a long time for a
+      partitioned table, consider switching to the <code class="ph codeph">COMPUTE INCREMENTAL STATS</code> syntax so that only
+      newly added partitions are analyzed each time.
+    </p>
+
+    <p class="p">
+        <strong class="ph b">Examples:</strong>
+      </p>
+
+    <p class="p">
+      This example shows two tables, <code class="ph codeph">T1</code> and <code class="ph codeph">T2</code>, with a small number distinct
+      values linked by a parent-child relationship between <code class="ph codeph">T1.ID</code> and <code class="ph codeph">T2.PARENT</code>.
+      <code class="ph codeph">T1</code> is tiny, while <code class="ph codeph">T2</code> has approximately 100K rows. Initially, the statistics
+      includes physical measurements such as the number of files, the total size, and size measurements for
+      fixed-length columns such as with the <code class="ph codeph">INT</code> type. Unknown values are represented by -1. After
+      running <code class="ph codeph">COMPUTE STATS</code> for each table, much more information is available through the
+      <code class="ph codeph">SHOW STATS</code> statements. If you were running a join query involving both of these tables, you
+      would need statistics for both tables to get the most effective optimization for the query.
+    </p>
+
+
+
+<pre class="pre codeblock"><code>[localhost:21000] &gt; show table stats t1;
+Query: show table stats t1
++-------+--------+------+--------+
+| #Rows | #Files | Size | Format |
++-------+--------+------+--------+
+| -1    | 1      | 33B  | TEXT   |
++-------+--------+------+--------+
+Returned 1 row(s) in 0.02s
+[localhost:21000] &gt; show table stats t2;
+Query: show table stats t2
++-------+--------+----------+--------+
+| #Rows | #Files | Size     | Format |
++-------+--------+----------+--------+
+| -1    | 28     | 960.00KB | TEXT   |
++-------+--------+----------+--------+
+Returned 1 row(s) in 0.01s
+[localhost:21000] &gt; show column stats t1;
+Query: show column stats t1
++--------+--------+------------------+--------+----------+----------+
+| Column | Type   | #Distinct Values | #Nulls | Max Size | Avg Size |
++--------+--------+------------------+--------+----------+----------+
+| id     | INT    | -1               | -1     | 4        | 4        |
+| s      | STRING | -1               | -1     | -1       | -1       |
++--------+--------+------------------+--------+----------+----------+
+Returned 2 row(s) in 1.71s
+[localhost:21000] &gt; show column stats t2;
+Query: show column stats t2
++--------+--------+------------------+--------+----------+----------+
+| Column | Type   | #Distinct Values | #Nulls | Max Size | Avg Size |
++--------+--------+------------------+--------+----------+----------+
+| parent | INT    | -1               | -1     | 4        | 4        |
+| s      | STRING | -1               | -1     | -1       | -1       |
++--------+--------+------------------+--------+----------+----------+
+Returned 2 row(s) in 0.01s
+[localhost:21000] &gt; compute stats t1;
+Query: compute stats t1
++-----------------------------------------+
+| summary                                 |
++-----------------------------------------+
+| Updated 1 partition(s) and 2 column(s). |
++-----------------------------------------+
+Returned 1 row(s) in 5.30s
+[localhost:21000] &gt; show table stats t1;
+Query: show table stats t1
++-------+--------+------+--------+
+| #Rows | #Files | Size | Format |
++-------+--------+------+--------+
+| 3     | 1      | 33B  | TEXT   |
++-------+--------+------+--------+
+Returned 1 row(s) in 0.01s
+[localhost:21000] &gt; show column stats t1;
+Query: show column stats t1
++--------+--------+------------------+--------+----------+----------+
+| Column | Type   | #Distinct Values | #Nulls | Max Size | Avg Size |
++--------+--------+------------------+--------+----------+----------+
+| id     | INT    | 3                | -1     | 4        | 4        |
+| s      | STRING | 3                | -1     | -1       | -1       |
++--------+--------+------------------+--------+----------+----------+
+Returned 2 row(s) in 0.02s
+[localhost:21000] &gt; compute stats t2;
+Query: compute stats t2
++-----------------------------------------+
+| summary                                 |
++-----------------------------------------+
+| Updated 1 partition(s) and 2 column(s). |
++-----------------------------------------+
+Returned 1 row(s) in 5.70s
+[localhost:21000] &gt; show table stats t2;
+Query: show table stats t2
++-------+--------+----------+--------+
+| #Rows | #Files | Size     | Format |
++-------+--------+----------+--------+
+| 98304 | 1      | 960.00KB | TEXT   |
++-------+--------+----------+--------+
+Returned 1 row(s) in 0.03s
+[localhost:21000] &gt; show column stats t2;
+Query: show column stats t2
++--------+--------+------------------+--------+----------+----------+
+| Column | Type   | #Distinct Values | #Nulls | Max Size | Avg Size |
++--------+--------+------------------+--------+----------+----------+
+| parent | INT    | 3                | -1     | 4        | 4        |
+| s      | STRING | 6                | -1     | 14       | 9.3      |
++--------+--------+------------------+--------+----------+----------+
+Returned 2 row(s) in 0.01s</code></pre>
+
+    <p class="p">
+      The following example shows how to use the <code class="ph codeph">INCREMENTAL</code> clause, available in Impala 2.1.0 and
+      higher. The <code class="ph codeph">COMPUTE INCREMENTAL STATS</code> syntax lets you collect statistics for newly added or
+      changed partitions, without rescanning the entire table.
+    </p>
+
+<pre class="pre codeblock"><code>-- Initially the table has no incremental stats, as indicated
+-- by -1 under #Rows and false under Incremental stats.
+show table stats item_partitioned;
++-------------+-------+--------+----------+--------------+---------+------------------
+| i_category  | #Rows | #Files | Size     | Bytes Cached | Format  | Incremental stats
++-------------+-------+--------+----------+--------------+---------+------------------
+| Books       | -1    | 1      | 223.74KB | NOT CACHED   | PARQUET | false
+| Children    | -1    | 1      | 230.05KB | NOT CACHED   | PARQUET | false
+| Electronics | -1    | 1      | 232.67KB | NOT CACHED   | PARQUET | false
+| Home        | -1    | 1      | 232.56KB | NOT CACHED   | PARQUET | false
+| Jewelry     | -1    | 1      | 223.72KB | NOT CACHED   | PARQUET | false
+| Men         | -1    | 1      | 231.25KB | NOT CACHED   | PARQUET | false
+| Music       | -1    | 1      | 237.90KB | NOT CACHED   | PARQUET | false
+| Shoes       | -1    | 1      | 234.90KB | NOT CACHED   | PARQUET | false
+| Sports      | -1    | 1      | 227.97KB | NOT CACHED   | PARQUET | false
+| Women       | -1    | 1      | 226.27KB | NOT CACHED   | PARQUET | false
+| Total       | -1    | 10     | 2.25MB   | 0B           |         |
++-------------+-------+--------+----------+--------------+---------+------------------
+
+-- After the first COMPUTE INCREMENTAL STATS,
+-- all partitions have stats.
+compute incremental stats item_partitioned;
++-------------------------------------------+
+| summary                                   |
++-------------------------------------------+
+| Updated 10 partition(s) and 21 column(s). |
++-------------------------------------------+
+show table stats item_partitioned;
++-------------+-------+--------+----------+--------------+---------+------------------
+| i_category  | #Rows | #Files | Size     | Bytes Cached | Format  | Incremental stats
++-------------+-------+--------+----------+--------------+---------+------------------
+| Books       | 1733  | 1      | 223.74KB | NOT CACHED   | PARQUET | true
+| Children    | 1786  | 1      | 230.05KB | NOT CACHED   | PARQUET | true
+| Electronics | 1812  | 1      | 232.67KB | NOT CACHED   | PARQUET | true
+| Home        | 1807  | 1      | 232.56KB | NOT CACHED   | PARQUET | true
+| Jewelry     | 1740  | 1      | 223.72KB | NOT CACHED   | PARQUET | true
+| Men         | 1811  | 1      | 231.25KB | NOT CACHED   | PARQUET | true
+| Music       | 1860  | 1      | 237.90KB | NOT CACHED   | PARQUET | true
+| Shoes       | 1835  | 1      | 234.90KB | NOT CACHED   | PARQUET | true
+| Sports      | 1783  | 1      | 227.97KB | NOT CACHED   | PARQUET | true
+| Women       | 1790  | 1      | 226.27KB | NOT CACHED   | PARQUET | true
+| Total       | 17957 | 10     | 2.25MB   | 0B           |         |
++-------------+-------+--------+----------+--------------+---------+------------------
+
+-- Add a new partition...
+alter table item_partitioned add partition (i_category='Camping');
+-- Add or replace files in HDFS outside of Impala,
+-- rendering the stats for a partition obsolete.
+!import_data_into_sports_partition.sh
+refresh item_partitioned;
+drop incremental stats item_partitioned partition (i_category='Sports');
+-- Now some partitions have incremental stats
+-- and some do not.
+show table stats item_partitioned;
++-------------+-------+--------+----------+--------------+---------+------------------
+| i_category  | #Rows | #Files | Size     | Bytes Cached | Format  | Incremental stats
++-------------+-------+--------+----------+--------------+---------+------------------
+| Books       | 1733  | 1      | 223.74KB | NOT CACHED   | PARQUET | true
+| Camping     | -1    | 1      | 408.02KB | NOT CACHED   | PARQUET | false
+| Children    | 1786  | 1      | 230.05KB | NOT CACHED   | PARQUET | true
+| Electronics | 1812  | 1      | 232.67KB | NOT CACHED   | PARQUET | true
+| Home        | 1807  | 1      | 232.56KB | NOT CACHED   | PARQUET | true
+| Jewelry     | 1740  | 1      | 223.72KB | NOT CACHED   | PARQUET | true
+| Men         | 1811  | 1      | 231.25KB | NOT CACHED   | PARQUET | true
+| Music       | 1860  | 1      | 237.90KB | NOT CACHED   | PARQUET | true
+| Shoes       | 1835  | 1      | 234.90KB | NOT CACHED   | PARQUET | true
+| Sports      | -1    | 1      | 227.97KB | NOT CACHED   | PARQUET | false
+| Women       | 1790  | 1      | 226.27KB | NOT CACHED   | PARQUET | true
+| Total       | 17957 | 11     | 2.65MB   | 0B           |         |
++-------------+-------+--------+----------+--------------+---------+------------------
+
+-- After another COMPUTE INCREMENTAL STATS,
+-- all partitions have incremental stats, and only the 2
+-- partitions without incremental stats were scanned.
+compute incremental stats item_partitioned;
++------------------------------------------+
+| summary                                  |
++------------------------------------------+
+| Updated 2 partition(s) and 21 column(s). |
++------------------------------------------+
+show table stats item_partitioned;
++-------------+-------+--------+----------+--------------+---------+------------------
+| i_category  | #Rows | #Files | Size     | Bytes Cached | Format  | Incremental stats
++-------------+-------+--------+----------+--------------+---------+------------------
+| Books       | 1733  | 1      | 223.74KB | NOT CACHED   | PARQUET | true
+| Camping     | 5328  | 1      | 408.02KB | NOT CACHED   | PARQUET | true
+| Children    | 1786  | 1      | 230.05KB | NOT CACHED   | PARQUET | true
+| Electronics | 1812  | 1      | 232.67KB | NOT CACHED   | PARQUET | true
+| Home        | 1807  | 1      | 232.56KB | NOT CACHED   | PARQUET | true
+| Jewelry     | 1740  | 1      | 223.72KB | NOT CACHED   | PARQUET | true
+| Men         | 1811  | 1      | 231.25KB | NOT CACHED   | PARQUET | true
+| Music       | 1860  | 1      | 237.90KB | NOT CACHED   | PARQUET | true
+| Shoes       | 1835  | 1      | 234.90KB | NOT CACHED   | PARQUET | true
+| Sports      | 1783  | 1      | 227.97KB | NOT CACHED   | PARQUET | true
+| Women       | 1790  | 1      | 226.27KB | NOT CACHED   | PARQUET | true
+| Total       | 17957 | 11     | 2.65MB   | 0B           |         |
++-------------+-------+--------+----------+--------------+---------+------------------
+</code></pre>
+
+    <p class="p">
+        <strong class="ph b">File format considerations:</strong>
+      </p>
+
+    <p class="p">
+      The <code class="ph codeph">COMPUTE STATS</code> statement works with tables created with any of the file formats supported
+      by Impala. See <a class="xref" href="impala_file_formats.html#file_formats">How Impala Works with Hadoop File Formats</a> for details about working with the
+      different file formats. The following considerations apply to <code class="ph codeph">COMPUTE STATS</code> depending on the
+      file format of the table.
+    </p>
+
+    <p class="p">
+      The <code class="ph codeph">COMPUTE STATS</code> statement works with text tables with no restrictions. These tables can be
+      created through either Impala or Hive.
+    </p>
+
+    <p class="p">
+      The <code class="ph codeph">COMPUTE STATS</code> statement works with Parquet tables. These tables can be created through
+      either Impala or Hive.
+    </p>
+
+    <p class="p">
+      The <code class="ph codeph">COMPUTE STATS</code> statement works with Avro tables without restriction in <span class="keyword">Impala 2.2</span>
+      and higher. In earlier releases, <code class="ph codeph">COMPUTE STATS</code> worked only for Avro tables created through Hive,
+      and required the <code class="ph codeph">CREATE TABLE</code> statement to use SQL-style column names and types rather than an
+      Avro-style schema specification.
+    </p>
+
+    <p class="p">
+      The <code class="ph codeph">COMPUTE STATS</code> statement works with RCFile tables with no restrictions. These tables can
+      be created through either Impala or Hive.
+    </p>
+
+    <p class="p">
+      The <code class="ph codeph">COMPUTE STATS</code> statement works with SequenceFile tables with no restrictions. These
+      tables can be created through either Impala or Hive.
+    </p>
+
+    <p class="p">
+      The <code class="ph codeph">COMPUTE STATS</code> statement works with partitioned tables, whether all the partitions use
+      the same file format, or some partitions are defined through <code class="ph codeph">ALTER TABLE</code> to use different
+      file formats.
+    </p>
+
+    <p class="p">
+        <strong class="ph b">Statement type:</strong> DDL
+      </p>
+
+    <p class="p">
+        <strong class="ph b">Cancellation:</strong> Certain multi-stage statements (<code class="ph codeph">CREATE TABLE AS SELECT</code> and
+        <code class="ph codeph">COMPUTE STATS</code>) can be cancelled during some stages, when running <code class="ph codeph">INSERT</code>
+        or <code class="ph codeph">SELECT</code> operations internally. To cancel this statement, use Ctrl-C from the
+        <span class="keyword cmdname">impala-shell</span> interpreter, the <span class="ph uicontrol">Cancel</span> button from the
+        <span class="ph uicontrol">Watch</span> page in Hue, or <span class="ph uicontrol">Cancel</span> from the list of
+        in-flight queries (for a particular node) on the <span class="ph uicontrol">Queries</span> tab in the Impala web UI
+        (port 25000).
+      </p>
+
+    <p class="p">
+        <strong class="ph b">Restrictions:</strong>
+      </p>
+
+    <div class="note note note_note"><span class="note__title notetitle">Note:</span>  Prior to Impala 1.4.0,
+          <code class="ph codeph">COMPUTE STATS</code> counted the number of
+          <code class="ph codeph">NULL</code> values in each column and recorded that figure
+        in the metastore database. Because Impala does not currently use the
+          <code class="ph codeph">NULL</code> count during query planning, Impala 1.4.0 and
+        higher speeds up the <code class="ph codeph">COMPUTE STATS</code> statement by
+        skipping this <code class="ph codeph">NULL</code> counting. </div>
+
+    <p class="p">
+        <strong class="ph b">Internal details:</strong>
+      </p>
+    <p class="p">
+      Behind the scenes, the <code class="ph codeph">COMPUTE STATS</code> statement
+      executes two statements: one to count the rows of each partition
+      in the table (or the entire table if unpartitioned) through the
+      <code class="ph codeph">COUNT(*)</code> function,
+      and another to count the approximate number of distinct values
+      in each column through the <code class="ph codeph">NDV()</code> function.
+      You might see these queries in your monitoring and diagnostic displays.
+      The same factors that affect the performance, scalability, and
+      execution of other queries (such as parallel execution, memory usage,
+      admission control, and timeouts) also apply to the queries run by the
+      <code class="ph codeph">COMPUTE STATS</code> statement.
+    </p>
+
+    <p class="p">
+        <strong class="ph b">HDFS permissions:</strong>
+      </p>
+    <p class="p">
+      The user ID that the <span class="keyword cmdname">impalad</span> daemon runs under,
+      typically the <code class="ph codeph">impala</code> user, must have read
+      permission for all affected files in the source directory:
+      all files in the case of an unpartitioned table or
+      a partitioned table in the case of <code class="ph codeph">COMPUTE STATS</code>;
+      or all the files in partitions without incremental stats in
+      the case of <code class="ph codeph">COMPUTE INCREMENTAL STATS</code>.
+      It must also have read and execute permissions for all
+      relevant directories holding the data files.
+      (Essentially, <code class="ph codeph">COMPUTE STATS</code> requires the
+      same permissions as the underlying <code class="ph codeph">SELECT</code> queries it runs
+      against the table.)
+    </p>
+
+    <p class="p">
+        <strong class="ph b">Kudu considerations:</strong>
+      </p>
+
+    <p class="p">
+      The <code class="ph codeph">COMPUTE STATS</code> statement applies to Kudu tables.
+      Impala does not compute the number of rows for each partition for
+      Kudu tables. Therefore, you do not need to re-run the operation when
+      you see -1 in the <code class="ph codeph"># Rows</code> column of the output from
+      <code class="ph codeph">SHOW TABLE STATS</code>. That column always shows -1 for
+      all Kudu tables. 
+    </p>
+
+    <p class="p">
+        <strong class="ph b">Related information:</strong>
+      </p>
+
+    <p class="p">
+      <a class="xref" href="impala_drop_stats.html#drop_stats">DROP STATS Statement</a>, <a class="xref" href="impala_show.html#show_table_stats">SHOW TABLE STATS Statement</a>,
+      <a class="xref" href="impala_show.html#show_column_stats">SHOW COLUMN STATS Statement</a>, <a class="xref" href="impala_perf_stats.html#perf_stats">Table and Column Statistics</a>
+    </p>
+  </div>
+<nav role="navigation" class="related-links"><div class="familylinks"><div class="parentlink"><strong>Parent topic:</strong> <a class="link" href="../topics/impala_langref_sql.html">Impala SQL Statements</a></div></div></nav></article></main></body></html>
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+<!DOCTYPE html
+  SYSTEM "about:legacy-compat">
+<html lang="en"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><meta charset="UTF-8"><meta name="copyright" content="(C) Copyright 2017"><meta name="DC.rights.owner" content="(C) Copyright 2017"><meta name="DC.Type" content="concept"><meta name="DC.Relation" scheme="URI" content="../topics/impala_components.html"><meta name="DC.Relation" scheme="URI" content="../topics/impala_development.html"><meta name="DC.Relation" scheme="URI" content="../topics/impala_hadoop.html"><meta name="prodname" content="Impala"><meta name="prodname" content="Impala"><meta name="version" content="Impala 2.8.x"><meta name="version" content="Impala 2.8.x"><meta name="DC.Format" content="XHTML"><meta name="DC.Identifier" content="concepts"><link rel="stylesheet" type="text/css" href="../commonltr.css"><title>Impala Concepts and Architecture</title></head><body id="concepts"><main role="main"><article role="article" aria-labelledby="ariaid-title1">
+
+  <h1 class="title topictitle1" id="ariaid-title1">Impala Concepts and Architecture</h1>
+  
+  
+
+  <div class="body conbody">
+
+    <p class="p">
+      The following sections provide background information to help you become productive using Impala and
+      its features. Where appropriate, the explanations include context to help understand how aspects of Impala
+      relate to other technologies you might already be familiar with, such as relational database management
+      systems and data warehouses, or other Hadoop components such as Hive, HDFS, and HBase.
+    </p>
+
+    <p class="p toc"></p>
+  </div>
+
+
+
+  
+
+  
+
+  
+
+  
+
+  
+
+  
+
+
+
+  
+
+
+
+  
+
+
+
+
+
+  
+<nav role="navigation" class="related-links"><ul class="ullinks"><li class="link ulchildlink"><strong><a href="../topics/impala_components.html">Components of the Impala Server</a></strong><br></li><li class="link ulchildlink"><strong><a href="../topics/impala_development.html">Developing Impala Applications</a></strong><br></li><li class="link ulchildlink"><strong><a href="../topics/impala_hadoop.html">How Impala Fits Into the Hadoop Ecosystem</a></strong><br></li></ul></nav></article></main></body></html>
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+  SYSTEM "about:legacy-compat">
+<html lang="en"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><meta charset="UTF-8"><meta name="copyright" content="(C) Copyright 2017"><meta name="DC.rights.owner" content="(C) Copyright 2017"><meta name="DC.Type" content="concept"><meta name="DC.Relation" scheme="URI" content="../topics/impala_functions.html"><meta name="prodname" content="Impala"><meta name="prodname" content="Impala"><meta name="version" content="Impala 2.8.x"><meta name="version" content="Impala 2.8.x"><meta name="DC.Format" content="XHTML"><meta name="DC.Identifier" content="conditional_functions"><link rel="stylesheet" type="text/css" href="../commonltr.css"><title>Impala Conditional Functions</title></head><body id="conditional_functions"><main role="main"><article role="article" aria-labelledby="ariaid-title1">
+
+  <h1 class="title topictitle1" id="ariaid-title1">Impala Conditional Functions</h1>
+  
+  
+
+  <div class="body conbody">
+
+    <p class="p">
+      Impala supports the following conditional functions for testing equality, comparison operators, and nullity:
+    </p>
+
+    <dl class="dl">
+      
+
+        <dt class="dt dlterm" id="conditional_functions__case">
+          <code class="ph codeph">CASE a WHEN b THEN c [WHEN d THEN e]... [ELSE f] END</code>
+        </dt>
+
+        <dd class="dd">
+          
+          <strong class="ph b">Purpose:</strong> Compares an expression to one or more possible values, and returns a corresponding result
+          when a match is found.
+          <p class="p">
+        <strong class="ph b">Return type:</strong> same as the initial argument value, except that integer values are promoted to
+        <code class="ph codeph">BIGINT</code> and floating-point values are promoted to <code class="ph codeph">DOUBLE</code>; use
+        <code class="ph codeph">CAST()</code> when inserting into a smaller numeric column
+      </p>
+          <p class="p">
+        <strong class="ph b">Usage notes:</strong>
+      </p>
+          <p class="p">
+            In this form of the <code class="ph codeph">CASE</code> expression, the initial value <code class="ph codeph">A</code>
+            being evaluated for each row it typically a column reference, or an expression involving
+            a column. This form can only compare against a set of specified values, not ranges,
+            multi-value comparisons such as <code class="ph codeph">BETWEEN</code> or <code class="ph codeph">IN</code>,
+            regular expressions, or <code class="ph codeph">NULL</code>.
+          </p>
+          <p class="p">
+        <strong class="ph b">Examples:</strong>
+      </p>
+          <p class="p">
+            Although this example is split across multiple lines, you can put any or all parts of a <code class="ph codeph">CASE</code> expression
+            on a single line, with no punctuation or other separators between the <code class="ph codeph">WHEN</code>,
+            <code class="ph codeph">ELSE</code>, and <code class="ph codeph">END</code> clauses.
+          </p>
+<pre class="pre codeblock"><code>select case x
+    when 1 then 'one'
+    when 2 then 'two'
+    when 0 then 'zero'
+    else 'out of range'
+  end
+    from t1;
+</code></pre>
+        </dd>
+
+      
+
+      
+
+        <dt class="dt dlterm" id="conditional_functions__case2">
+          <code class="ph codeph">CASE WHEN a THEN b [WHEN c THEN d]... [ELSE e] END</code>
+        </dt>
+
+        <dd class="dd">
+          
+          <strong class="ph b">Purpose:</strong> Tests whether any of a sequence of expressions is true, and returns a corresponding
+          result for the first true expression.
+          <p class="p">
+        <strong class="ph b">Return type:</strong> same as the initial argument value, except that integer values are promoted to
+        <code class="ph codeph">BIGINT</code> and floating-point values are promoted to <code class="ph codeph">DOUBLE</code>; use
+        <code class="ph codeph">CAST()</code> when inserting into a smaller numeric column
+      </p>
+          <p class="p">
+        <strong class="ph b">Usage notes:</strong>
+      </p>
+          <p class="p">
+            <code class="ph codeph">CASE</code> expressions without an initial test value have more flexibility.
+            For example, they can test different columns in different <code class="ph codeph">WHEN</code> clauses,
+            or use comparison operators such as <code class="ph codeph">BETWEEN</code>, <code class="ph codeph">IN</code> and <code class="ph codeph">IS NULL</code>
+            rather than comparing against discrete values.
+          </p>
+          <p class="p">
+            <code class="ph codeph">CASE</code> expressions are often the foundation of long queries that
+            summarize and format results for easy-to-read reports. For example, you might
+            use a <code class="ph codeph">CASE</code> function call to turn values from a numeric column
+            into category strings corresponding to integer values, or labels such as <span class="q">"Small"</span>,
+            <span class="q">"Medium"</span> and <span class="q">"Large"</span> based on ranges. Then subsequent parts of the
+            query might aggregate based on the transformed values, such as how many
+            values are classified as small, medium, or large. You can also use <code class="ph codeph">CASE</code>
+            to signal problems with out-of-bounds values, <code class="ph codeph">NULL</code> values,
+            and so on.
+          </p>
+          <p class="p">
+            By using operators such as <code class="ph codeph">OR</code>, <code class="ph codeph">IN</code>,
+            <code class="ph codeph">REGEXP</code>, and so on in <code class="ph codeph">CASE</code> expressions,
+            you can build extensive tests and transformations into a single query.
+            Therefore, applications that construct SQL statements often rely heavily on <code class="ph codeph">CASE</code>
+            calls in the generated SQL code.
+          </p>
+          <p class="p">
+            Because this flexible form of the <code class="ph codeph">CASE</code> expressions allows you to perform
+            many comparisons and call multiple functions when evaluating each row, be careful applying
+            elaborate <code class="ph codeph">CASE</code> expressions to queries that process large amounts of data.
+            For example, when practical, evaluate and transform values through <code class="ph codeph">CASE</code>
+            after applying operations such as aggregations that reduce the size of the result set;
+            transform numbers to strings after performing joins with the original numeric values.
+          </p>
+          <p class="p">
+        <strong class="ph b">Examples:</strong>
+      </p>
+          <p class="p">
+            Although this example is split across multiple lines, you can put any or all parts of a <code class="ph codeph">CASE</code> expression
+            on a single line, with no punctuation or other separators between the <code class="ph codeph">WHEN</code>,
+            <code class="ph codeph">ELSE</code>, and <code class="ph codeph">END</code> clauses.
+          </p>
+<pre class="pre codeblock"><code>select case
+    when dayname(now()) in ('Saturday','Sunday') then 'result undefined on weekends'
+    when x &gt; y then 'x greater than y'
+    when x = y then 'x and y are equal'
+    when x is null or y is null then 'one of the columns is null'
+    else null
+  end
+    from t1;
+</code></pre>
+        </dd>
+
+      
+
+      
+
+        <dt class="dt dlterm" id="conditional_functions__coalesce">
+          <code class="ph codeph">coalesce(type v1, type v2, ...)</code>
+        </dt>
+
+        <dd class="dd">
+          
+          <strong class="ph b">Purpose:</strong> Returns the first specified argument that is not <code class="ph codeph">NULL</code>, or
+          <code class="ph codeph">NULL</code> if all arguments are <code class="ph codeph">NULL</code>.
+          <p class="p">
+        <strong class="ph b">Return type:</strong> same as the initial argument value, except that integer values are promoted to
+        <code class="ph codeph">BIGINT</code> and floating-point values are promoted to <code class="ph codeph">DOUBLE</code>; use
+        <code class="ph codeph">CAST()</code> when inserting into a smaller numeric column
+      </p>
+        </dd>
+
+      
+
+      
+
+        <dt class="dt dlterm" id="conditional_functions__decode">
+          <code class="ph codeph">decode(type expression, type search1, type result1 [, type search2, type result2 ...] [, type
+          default] )</code>
+        </dt>
+
+        <dd class="dd">
+          
+          <strong class="ph b">Purpose:</strong> Compares an expression to one or more possible values, and returns a corresponding result
+          when a match is found.
+          <p class="p">
+        <strong class="ph b">Return type:</strong> same as the initial argument value, except that integer values are promoted to
+        <code class="ph codeph">BIGINT</code> and floating-point values are promoted to <code class="ph codeph">DOUBLE</code>; use
+        <code class="ph codeph">CAST()</code> when inserting into a smaller numeric column
+      </p>
+          <p class="p">
+        <strong class="ph b">Usage notes:</strong>
+      </p>
+          <p class="p">
+            Can be used as shorthand for a <code class="ph codeph">CASE</code> expression.
+          </p>
+          <p class="p">
+            The original expression and the search expressions must of the same type or convertible types. The
+            result expression can be a different type, but all result expressions must be of the same type.
+          </p>
+          <p class="p">
+            Returns a successful match If the original expression is <code class="ph codeph">NULL</code> and a search expression
+            is also <code class="ph codeph">NULL</code>. the
+          </p>
+          <p class="p">
+            Returns <code class="ph codeph">NULL</code> if the final <code class="ph codeph">default</code> value is omitted and none of the
+            search expressions match the original expression.
+          </p>
+          <p class="p">
+        <strong class="ph b">Examples:</strong>
+      </p>
+          <p class="p">
+            The following example translates numeric day values into descriptive names:
+          </p>
+<pre class="pre codeblock"><code>SELECT event, decode(day_of_week, 1, "Monday", 2, "Tuesday", 3, "Wednesday",
+  4, "Thursday", 5, "Friday", 6, "Saturday", 7, "Sunday", "Unknown day")
+  FROM calendar;
+</code></pre>
+        </dd>
+
+      
+
+      
+
+        <dt class="dt dlterm" id="conditional_functions__if">
+          <code class="ph codeph">if(boolean condition, type ifTrue, type ifFalseOrNull)</code>
+        </dt>
+
+        <dd class="dd">
+          
+          <strong class="ph b">Purpose:</strong> Tests an expression and returns a corresponding result depending on whether the result is
+          true, false, or <code class="ph codeph">NULL</code>.
+          <p class="p">
+            <strong class="ph b">Return type:</strong> Same as the <code class="ph codeph">ifTrue</code> argument value
+          </p>
+        </dd>
+
+      
+
+      
+
+        <dt class="dt dlterm" id="conditional_functions__ifnull">
+          <code class="ph codeph">ifnull(type a, type ifNull)</code>
+        </dt>
+
+        <dd class="dd">
+          
+          <strong class="ph b">Purpose:</strong> Alias for the <code class="ph codeph">isnull()</code> function, with the same behavior. To simplify
+          porting SQL with vendor extensions to Impala.
+          <p class="p">
+        <strong class="ph b">Added in:</strong> Impala 1.3.0
+      </p>
+        </dd>
+
+      
+
+      
+
+        <dt class="dt dlterm" id="conditional_functions__isfalse">
+          <code class="ph codeph">isfalse(<var class="keyword varname">boolean</var>)</code>
+        </dt>
+
+        <dd class="dd">
+          
+          <strong class="ph b">Purpose:</strong> Tests if a Boolean expression is <code class="ph codeph">false</code> or not.
+          Returns <code class="ph codeph">true</code> if so.
+          If the argument is <code class="ph codeph">NULL</code>, returns <code class="ph codeph">false</code>.
+          Identical to <code class="ph codeph">isnottrue()</code>, except it returns the opposite value for a <code class="ph codeph">NULL</code> argument.
+          <p class="p">
+        <strong class="ph b">Return type:</strong> <code class="ph codeph">BOOLEAN</code>
+      </p>
+          <p class="p">
+        <strong class="ph b">Added in:</strong> <span class="keyword">Impala 2.2.0</span>
+      </p>
+        </dd>
+
+      
+
+      
+
+        <dt class="dt dlterm" id="conditional_functions__isnotfalse">
+          <code class="ph codeph">isnotfalse(<var class="keyword varname">boolean</var>)</code>
+        </dt>
+
+        <dd class="dd">
+          
+          <strong class="ph b">Purpose:</strong> Tests if a Boolean expression is not <code class="ph codeph">false</code> (that is, either <code class="ph codeph">true</code> or <code class="ph codeph">NULL</code>).
+          Returns <code class="ph codeph">true</code> if so.
+          If the argument is <code class="ph codeph">NULL</code>, returns <code class="ph codeph">true</code>.
+          Identical to <code class="ph codeph">istrue()</code>, except it returns the opposite value for a <code class="ph codeph">NULL</code> argument.
+          <p class="p">
+        <strong class="ph b">Return type:</strong> <code class="ph codeph">BOOLEAN</code>
+      </p>
+          <p class="p">
+        <strong class="ph b">Usage notes:</strong> Primarily for compatibility with code containing industry extensions to SQL.
+      </p>
+          <p class="p">
+        <strong class="ph b">Added in:</strong> <span class="keyword">Impala 2.2.0</span>
+      </p>
+        </dd>
+
+      
+
+      
+
+        <dt class="dt dlterm" id="conditional_functions__isnottrue">
+          <code class="ph codeph">isnottrue(<var class="keyword varname">boolean</var>)</code>
+        </dt>
+
+        <dd class="dd">
+          
+          <strong class="ph b">Purpose:</strong> Tests if a Boolean expression is not <code class="ph codeph">true</code> (that is, either <code class="ph codeph">false</code> or <code class="ph codeph">NULL</code>).
+          Returns <code class="ph codeph">true</code> if so.
+          If the argument is <code class="ph codeph">NULL</code>, returns <code class="ph codeph">true</code>.
+          Identical to <code class="ph codeph">isfalse()</code>, except it returns the opposite value for a <code class="ph codeph">NULL</code> argument.
+          <p class="p">
+        <strong class="ph b">Return type:</strong> <code class="ph codeph">BOOLEAN</code>
+      </p>
+          <p class="p">
+        <strong class="ph b">Added in:</strong> <span class="keyword">Impala 2.2.0</span>
+      </p>
+        </dd>
+
+      
+
+      
+
+        <dt class="dt dlterm" id="conditional_functions__isnull">
+          <code class="ph codeph">isnull(type a, type ifNull)</code>
+        </dt>
+
+        <dd class="dd">
+          
+          <strong class="ph b">Purpose:</strong> Tests if an expression is <code class="ph codeph">NULL</code>, and returns the expression result value
+          if not. If the first argument is <code class="ph codeph">NULL</code>, returns the second argument.
+          <p class="p">
+            <strong class="ph b">Compatibility notes:</strong> Equivalent to the <code class="ph codeph">nvl()</code> function from Oracle Database or
+            <code class="ph codeph">ifnull()</code> from MySQL. The <code class="ph codeph">nvl()</code> and <code class="ph codeph">ifnull()</code>
+            functions are also available in Impala.
+          </p>
+          <p class="p">
+            <strong class="ph b">Return type:</strong> Same as the first argument value
+          </p>
+        </dd>
+
+      
+
+      
+
+        <dt class="dt dlterm" id="conditional_functions__istrue">
+          <code class="ph codeph">istrue(<var class="keyword varname">boolean</var>)</code>
+        </dt>
+
+        <dd class="dd">
+          
+          <strong class="ph b">Purpose:</strong> Tests if a Boolean expression is <code class="ph codeph">true</code> or not.
+          Returns <code class="ph codeph">true</code> if so.
+          If the argument is <code class="ph codeph">NULL</code>, returns <code class="ph codeph">false</code>.
+          Identical to <code class="ph codeph">isnotfalse()</code>, except it returns the opposite value for a <code class="ph codeph">NULL</code> argument.
+          <p class="p">
+        <strong class="ph b">Return type:</strong> <code class="ph codeph">BOOLEAN</code>
+      </p>
+          <p class="p">
+        <strong class="ph b">Usage notes:</strong> Primarily for compatibility with code containing industry extensions to SQL.
+      </p>
+          <p class="p">
+        <strong class="ph b">Added in:</strong> <span class="keyword">Impala 2.2.0</span>
+      </p>
+        </dd>
+
+      
+
+      
+
+        <dt class="dt dlterm" id="conditional_functions__nonnullvalue">
+          <code class="ph codeph">nonnullvalue(<var class="keyword varname">expression</var>)</code>
+        </dt>
+
+        <dd class="dd">
+          
+          <strong class="ph b">Purpose:</strong> Tests if an expression (of any type) is <code class="ph codeph">NULL</code> or not.
+          Returns <code class="ph codeph">false</code> if so.
+          The converse of <code class="ph codeph">nullvalue()</code>.
+          <p class="p">
+        <strong class="ph b">Return type:</strong> <code class="ph codeph">BOOLEAN</code>
+      </p>
+          <p class="p">
+        <strong class="ph b">Usage notes:</strong> Primarily for compatibility with code containing industry extensions to SQL.
+      </p>
+          <p class="p">
+        <strong class="ph b">Added in:</strong> <span class="keyword">Impala 2.2.0</span>
+      </p>
+        </dd>
+
+      
+
+      
+
+        <dt class="dt dlterm" id="conditional_functions__nullif">
+          <code class="ph codeph">nullif(<var class="keyword varname">expr1</var>,<var class="keyword varname">expr2</var>)</code>
+        </dt>
+
+        <dd class="dd">
+          
+          <strong class="ph b">Purpose:</strong> Returns <code class="ph codeph">NULL</code> if the two specified arguments are equal. If the specified
+          arguments are not equal, returns the value of <var class="keyword varname">expr1</var>. The data types of the expressions
+          must be compatible, according to the conversion rules from <a class="xref" href="impala_datatypes.html#datatypes">Data Types</a>.
+          You cannot use an expression that evaluates to <code class="ph codeph">NULL</code> for <var class="keyword varname">expr1</var>; that
+          way, you can distinguish a return value of <code class="ph codeph">NULL</code> from an argument value of
+          <code class="ph codeph">NULL</code>, which would never match <var class="keyword varname">expr2</var>.
+          <p class="p">
+            <strong class="ph b">Usage notes:</strong> This function is effectively shorthand for a <code class="ph codeph">CASE</code> expression of
+            the form:
+          </p>
+<pre class="pre codeblock"><code>CASE
+  WHEN <var class="keyword varname">expr1</var> = <var class="keyword varname">expr2</var> THEN NULL
+  ELSE <var class="keyword varname">expr1</var>
+END</code></pre>
+          <p class="p">
+            It is commonly used in division expressions, to produce a <code class="ph codeph">NULL</code> result instead of a
+            divide-by-zero error when the divisor is equal to zero:
+          </p>
+<pre class="pre codeblock"><code>select 1.0 / nullif(c1,0) as reciprocal from t1;</code></pre>
+          <p class="p">
+            You might also use it for compatibility with other database systems that support the same
+            <code class="ph codeph">NULLIF()</code> function.
+          </p>
+          <p class="p">
+        <strong class="ph b">Return type:</strong> same as the initial argument value, except that integer values are promoted to
+        <code class="ph codeph">BIGINT</code> and floating-point values are promoted to <code class="ph codeph">DOUBLE</code>; use
+        <code class="ph codeph">CAST()</code> when inserting into a smaller numeric column
+      </p>
+          <p class="p">
+        <strong class="ph b">Added in:</strong> Impala 1.3.0
+      </p>
+        </dd>
+
+      
+
+      
+
+        <dt class="dt dlterm" id="conditional_functions__nullifzero">
+          <code class="ph codeph">nullifzero(<var class="keyword varname">numeric_expr</var>)</code>
+        </dt>
+
+        <dd class="dd">
+          
+          <strong class="ph b">Purpose:</strong> Returns <code class="ph codeph">NULL</code> if the numeric expression evaluates to 0, otherwise returns
+          the result of the expression.
+          <p class="p">
+            <strong class="ph b">Usage notes:</strong> Used to avoid error conditions such as divide-by-zero in numeric calculations.
+            Serves as shorthand for a more elaborate <code class="ph codeph">CASE</code> expression, to simplify porting SQL with
+            vendor extensions to Impala.
+          </p>
+          <p class="p">
+        <strong class="ph b">Return type:</strong> same as the initial argument value, except that integer values are promoted to
+        <code class="ph codeph">BIGINT</code> and floating-point values are promoted to <code class="ph codeph">DOUBLE</code>; use
+        <code class="ph codeph">CAST()</code> when inserting into a smaller numeric column
+      </p>
+          <p class="p">
+        <strong class="ph b">Added in:</strong> Impala 1.3.0
+      </p>
+        </dd>
+
+      
+
+      
+
+        <dt class="dt dlterm" id="conditional_functions__nullvalue">
+          <code class="ph codeph">nullvalue(<var class="keyword varname">expression</var>)</code>
+        </dt>
+
+        <dd class="dd">
+          
+          <strong class="ph b">Purpose:</strong> Tests if an expression (of any type) is <code class="ph codeph">NULL</code> or not.
+          Returns <code class="ph codeph">true</code> if so.
+          The converse of <code class="ph codeph">nonnullvalue()</code>.
+          <p class="p">
+        <strong class="ph b">Return type:</strong> <code class="ph codeph">BOOLEAN</code>
+      </p>
+          <p class="p">
+        <strong class="ph b">Usage notes:</strong> Primarily for compatibility with code containing industry extensions to SQL.
+      </p>
+          <p class="p">
+        <strong class="ph b">Added in:</strong> <span class="keyword">Impala 2.2.0</span>
+      </p>
+        </dd>
+
+      
+
+      
+
+        <dt class="dt dlterm" id="conditional_functions__nvl">
+          <code class="ph codeph">nvl(type a, type ifNull)</code>
+        </dt>
+
+        <dd class="dd">
+          
+          <strong class="ph b">Purpose:</strong> Alias for the <code class="ph codeph">isnull()</code> function. Tests if an expression is
+          <code class="ph codeph">NULL</code>, and returns the expression result value if not. If the first argument is
+          <code class="ph codeph">NULL</code>, returns the second argument. Equivalent to the <code class="ph codeph">nvl()</code> function
+          from Oracle Database or <code class="ph codeph">ifnull()</code> from MySQL.
+          <p class="p">
+            <strong class="ph b">Return type:</strong> Same as the first argument value
+          </p>
+          <p class="p">
+        <strong class="ph b">Added in:</strong> Impala 1.1
+      </p>
+        </dd>
+
+      
+
+      
+
+        <dt class="dt dlterm" id="conditional_functions__zeroifnull">
+          <code class="ph codeph">zeroifnull(<var class="keyword varname">numeric_expr</var>)</code>
+        </dt>
+
+        <dd class="dd">
+          
+          <strong class="ph b">Purpose:</strong> Returns 0 if the numeric expression evaluates to <code class="ph codeph">NULL</code>, otherwise returns
+          the result of the expression.
+          <p class="p">
+            <strong class="ph b">Usage notes:</strong> Used to avoid unexpected results due to unexpected propagation of
+            <code class="ph codeph">NULL</code> values in numeric calculations. Serves as shorthand for a more elaborate
+            <code class="ph codeph">CASE</code> expression, to simplify porting SQL with vendor extensions to Impala.
+          </p>
+          <p class="p">
+        <strong class="ph b">Return type:</strong> same as the initial argument value, except that integer values are promoted to
+        <code class="ph codeph">BIGINT</code> and floating-point values are promoted to <code class="ph codeph">DOUBLE</code>; use
+        <code class="ph codeph">CAST()</code> when inserting into a smaller numeric column
+      </p>
+          <p class="p">
+        <strong class="ph b">Added in:</strong> Impala 1.3.0
+      </p>
+        </dd>
+
+      
+    </dl>
+  </div>
+<nav role="navigation" class="related-links"><div class="familylinks"><div class="parentlink"><strong>Parent topic:</strong> <a class="link" href="../topics/impala_functions.html">Impala Built-In Functions</a></div></div></nav></article></main></body></html>
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http://git-wip-us.apache.org/repos/asf/incubator-impala/blob/75c46918/docs/build/html/topics/impala_config.html
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+<!DOCTYPE html
+  SYSTEM "about:legacy-compat">
+<html lang="en"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><meta charset="UTF-8"><meta name="copyright" content="(C) Copyright 2017"><meta name="DC.rights.owner" content="(C) Copyright 2017"><meta name="DC.Type" content="concept"><meta name="DC.Relation" scheme="URI" content="../topics/impala_config_performance.html"><meta name="DC.Relation" scheme="URI" content="../topics/impala_odbc.html"><meta name="DC.Relation" scheme="URI" content="../topics/impala_jdbc.html"><meta name="prodname" content="Impala"><meta name="prodname" content="Impala"><meta name="version" content="Impala 2.8.x"><meta name="version" content="Impala 2.8.x"><meta name="DC.Format" content="XHTML"><meta name="DC.Identifier" content="config"><link rel="stylesheet" type="text/css" href="../commonltr.css"><title>Managing Impala</title></head><body id="config"><main role="main"><article role="article" aria-labelledby="ariaid-title1">
+
+  <h1 class="title topictitle1" id="ariaid-title1">Managing Impala</h1>
+  
+
+  <div class="body conbody">
+
+    <p class="p">
+      This section explains how to configure Impala to accept connections from applications that use popular
+      programming APIs:
+    </p>
+
+    <ul class="ul">
+      <li class="li">
+        <a class="xref" href="impala_config_performance.html#config_performance">Post-Installation Configuration for Impala</a>
+      </li>
+
+      <li class="li">
+        <a class="xref" href="impala_odbc.html#impala_odbc">Configuring Impala to Work with ODBC</a>
+      </li>
+
+      <li class="li">
+        <a class="xref" href="impala_jdbc.html#impala_jdbc">Configuring Impala to Work with JDBC</a>
+      </li>
+    </ul>
+
+    <p class="p">
+      This type of configuration is especially useful when using Impala in combination with Business Intelligence
+      tools, which use these standard interfaces to query different kinds of database and Big Data systems.
+    </p>
+
+    <p class="p">
+      You can also configure these other aspects of Impala:
+    </p>
+
+    <ul class="ul">
+      <li class="li">
+        <a class="xref" href="impala_security.html#security">Impala Security</a>
+      </li>
+
+      <li class="li">
+        <a class="xref" href="impala_config_options.html#config_options">Modifying Impala Startup Options</a>
+      </li>
+    </ul>
+  </div>
+<nav role="navigation" class="related-links"><ul class="ullinks"><li class="link ulchildlink"><strong><a href="../topics/impala_config_performance.html">Post-Installation Configuration for Impala</a></strong><br></li><li class="link ulchildlink"><strong><a href="../topics/impala_odbc.html">Configuring Impala to Work with ODBC</a></strong><br></li><li class="link ulchildlink"><strong><a href="../topics/impala_jdbc.html">Configuring Impala to Work with JDBC</a></strong><br></li></ul></nav></article></main></body></html>
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