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.vaug...@gmail.com> Authored: Sat Oct 28 15:57:15 2017 -0700 Committer: Jon Haddad <j...@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 --------------------------------------------------------------------- To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org For additional commands, e-mail: commits-h...@cassandra.apache.org
