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From rustyrazorbl...@apache.org
Subject cassandra git commit: Document speculative_retry on the Cassandra DDL page
Date Mon, 30 Oct 2017 23:44:47 GMT
Repository: cassandra
Updated Branches:
  refs/heads/trunk 569c6abcf -> bc5ad7bfa


Document speculative_retry on the Cassandra DDL page

Patch by Jordan Vaughan; Reviewed by Jon Haddad
for CASSANDRA-13872


Project: http://git-wip-us.apache.org/repos/asf/cassandra/repo
Commit: http://git-wip-us.apache.org/repos/asf/cassandra/commit/bc5ad7bf
Tree: http://git-wip-us.apache.org/repos/asf/cassandra/tree/bc5ad7bf
Diff: http://git-wip-us.apache.org/repos/asf/cassandra/diff/bc5ad7bf

Branch: refs/heads/trunk
Commit: bc5ad7bfa949cd566919e8ba28b327514d98c132
Parents: 569c6ab
Author: Jordan Vaughan <jordan.t.vaughan@gmail.com>
Authored: Sat Oct 28 15:57:15 2017 -0700
Committer: Jon Haddad <jon@jonhaddad.com>
Committed: Mon Oct 30 16:44:02 2017 -0700

----------------------------------------------------------------------
 doc/source/cql/ddl.rst | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/cassandra/blob/bc5ad7bf/doc/source/cql/ddl.rst
----------------------------------------------------------------------
diff --git a/doc/source/cql/ddl.rst b/doc/source/cql/ddl.rst
index 6361983..a09265b 100644
--- a/doc/source/cql/ddl.rst
+++ b/doc/source/cql/ddl.rst
@@ -462,6 +462,9 @@ A table supports the following options:
 |                                |          |             | belonging to the same data center
than the read           |
 |                                |          |             | coordinator for the purpose of
read repairs.              |
 +--------------------------------+----------+-------------+-----------------------------------------------------------+
+| ``speculative_retry``          | *simple* | 99PERCENTILE| :ref:`Speculative retry options
                          |
+|                                |          |             | <speculative-retry-options>`.
                            |
++--------------------------------+----------+-------------+-----------------------------------------------------------+
 | ``gc_grace_seconds``           | *simple* | 864000      | Time to wait before garbage collecting
tombstones         |
 |                                |          |             | (deletion markers).         
                             |
 +--------------------------------+----------+-------------+-----------------------------------------------------------+
@@ -482,6 +485,34 @@ A table supports the following options:
 | ``memtable_flush_period_in_ms``| *simple* | 0           | Time (in ms) before Cassandra
flushes memtables to disk.  |
 +--------------------------------+----------+-------------+-----------------------------------------------------------+
 
+.. _speculative-retry-options:
+
+Speculative retry options
+#########################
+
+By default, Cassandra read coordinators only query as many replicas as necessary to satisfy
+consistency levels: one for consistency level ``ONE``, a quorum for ``QUORUM``, and so on.
+``speculative_retry`` determines when coordinators may query additional replicas, which is
useful
+when replicas are slow or unresponsive.  The following are legal values:
+
+========================= ================ =============================================================================
+ Format                    Example          Description
+========================= ================ =============================================================================
+ ``XPERCENTILE``           90.5PERCENTILE   Coordinators record average per-table response
times for all replicas.
+                                            If a replica takes longer than ``X`` percent
of this table's average
+                                            response time, the coordinator queries an additional
replica.
+                                            ``X`` must be between 0 and 100.
+ ``Yms``                   25ms             If a replica takes more than ``Y`` milliseconds
to respond,
+                                            the coordinator queries an additional replica.
+ ``ALWAYS``                                 Coordinators always query all replicas.
+ ``NONE``                                   Coordinators never query additional replicas.
+========================= ================ =============================================================================
+
+This setting does not affect reads with consistency level ``ALL`` because they already query
all replicas.
+
+Note that frequently reading from additional replicas can hurt cluster performance.
+When in doubt, keep the default ``99PERCENTILE``.
+
 .. _cql-compaction-options:
 
 Compaction options


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