Repository: cassandra Updated Branches: refs/heads/trunk 0e23d175a -> 6dfc1e7ee
Deprecate memtable_cleanup_threshold and set memtable_flush_writers default to 2. Patch by Ariel Weisberg; reviewed by marcuse for CASSANDRA-12228 Project: http://git-wip-us.apache.org/repos/asf/cassandra/repo Commit: http://git-wip-us.apache.org/repos/asf/cassandra/commit/6dfc1e7e Tree: http://git-wip-us.apache.org/repos/asf/cassandra/tree/6dfc1e7e Diff: http://git-wip-us.apache.org/repos/asf/cassandra/diff/6dfc1e7e Branch: refs/heads/trunk Commit: 6dfc1e7eeba539774784dfd650d3e1de6785c938 Parents: 0e23d17 Author: Ariel Weisberg <[email protected]> Authored: Mon Aug 1 21:30:21 2016 -0400 Committer: Marcus Eriksson <[email protected]> Committed: Thu Aug 4 14:30:04 2016 +0200 ---------------------------------------------------------------------- CHANGES.txt | 1 + conf/cassandra.yaml | 37 ++++++++++++++++---- .../org/apache/cassandra/config/Config.java | 2 +- .../cassandra/config/DatabaseDescriptor.java | 11 ++++++ 4 files changed, 43 insertions(+), 8 deletions(-) ---------------------------------------------------------------------- http://git-wip-us.apache.org/repos/asf/cassandra/blob/6dfc1e7e/CHANGES.txt ---------------------------------------------------------------------- diff --git a/CHANGES.txt b/CHANGES.txt index f5ca8f1..91e065f 100644 --- a/CHANGES.txt +++ b/CHANGES.txt @@ -1,4 +1,5 @@ 3.10 + * Deprecate memtable_cleanup_threshold and update default for memtable_flush_writers (CASSANDRA-12228) * Upgrade to OHC 0.4.4 (CASSANDRA-12133) * Add version command to cassandra-stress (CASSANDRA-12258) * Create compaction-stress tool (CASSANDRA-11844) http://git-wip-us.apache.org/repos/asf/cassandra/blob/6dfc1e7e/conf/cassandra.yaml ---------------------------------------------------------------------- diff --git a/conf/cassandra.yaml b/conf/cassandra.yaml index aaabc2b..e724941 100644 --- a/conf/cassandra.yaml +++ b/conf/cassandra.yaml @@ -471,6 +471,10 @@ concurrent_materialized_view_writes: 32 # memtable_heap_space_in_mb: 2048 # memtable_offheap_space_in_mb: 2048 +# memtable_cleanup_threshold is deprecated. The default calculation +# is the only reasonable choice. See the comments on memtable_flush_writers +# for more information. +# # Ratio of occupied non-flushing memtable size to total permitted size # that will trigger a flush of the largest memtable. Larger mct will # mean larger flushes and hence less compaction, but also less concurrent @@ -504,15 +508,34 @@ memtable_allocation_type: heap_buffers # # commitlog_total_space_in_mb: 8192 -# This sets the amount of memtable flush writer threads. These will -# be blocked by disk io, and each one will hold a memtable in memory -# while blocked. +# This sets the number of memtable flush writer threads per disk +# as well as the total number of memtables that can be flushed concurrently. +# These are generally a combination of compute and IO bound. +# +# Memtable flushing is more CPU efficient than memtable ingest and a single thread +# can keep up with the ingest rate of a whole server on a single fast disk +# until it temporarily becomes IO bound under contention typically with compaction. +# At that point you need multiple flush threads. At some point in the future +# it may become CPU bound all the time. +# +# You can tell if flushing is falling behind using the MemtablePool.BlockedOnAllocation +# metric which should be 0, but will be non-zero if threads are blocked waiting on flushing +# to free memory. +# +# memtable_flush_writers defaults to two for a single data directory. +# This means that two memtables can be flushed concurrently to the single data directory. +# If you have multiple data directories the default is one memtable flushing at a time +# but the flush will use a thread per data directory so you will get two or more writers. +# +# Two is generally enough to flush on a fast disk [array] mounted as a single data directory. +# Adding more flush writers will result in smaller more frequent flushes that introduce more +# compaction overhead. # -# memtable_flush_writers defaults to one per data_file_directory. +# There is a direct tradeoff between number of memtables that can be flushed concurrently +# and flush size and frequency. More is not better you just need enough flush writers +# to never stall waiting for flushing to free memory. # -# If your data directories are backed by SSD, you can increase this, but -# avoid having memtable_flush_writers * data_file_directories > number of cores -#memtable_flush_writers: 1 +#memtable_flush_writers: 2 # Total space to use for change-data-capture logs on disk. # http://git-wip-us.apache.org/repos/asf/cassandra/blob/6dfc1e7e/src/java/org/apache/cassandra/config/Config.java ---------------------------------------------------------------------- diff --git a/src/java/org/apache/cassandra/config/Config.java b/src/java/org/apache/cassandra/config/Config.java index a4b42b7..64f06b9 100644 --- a/src/java/org/apache/cassandra/config/Config.java +++ b/src/java/org/apache/cassandra/config/Config.java @@ -113,7 +113,7 @@ public class Config @Deprecated public Integer concurrent_replicates = null; - public Integer memtable_flush_writers = 1; + public Integer memtable_flush_writers = null; public Integer memtable_heap_space_in_mb; public Integer memtable_offheap_space_in_mb; public Float memtable_cleanup_threshold = null; http://git-wip-us.apache.org/repos/asf/cassandra/blob/6dfc1e7e/src/java/org/apache/cassandra/config/DatabaseDescriptor.java ---------------------------------------------------------------------- diff --git a/src/java/org/apache/cassandra/config/DatabaseDescriptor.java b/src/java/org/apache/cassandra/config/DatabaseDescriptor.java index caf3925..d74d4ad 100644 --- a/src/java/org/apache/cassandra/config/DatabaseDescriptor.java +++ b/src/java/org/apache/cassandra/config/DatabaseDescriptor.java @@ -666,11 +666,22 @@ public class DatabaseDescriptor if (conf.hints_directory.equals(conf.saved_caches_directory)) throw new ConfigurationException("saved_caches_directory must not be the same as the hints_directory", false); + if (conf.memtable_flush_writers == null) + { + conf.memtable_flush_writers = conf.data_file_directories.length == 1 ? 2 : 1; + } + if (conf.memtable_flush_writers < 1) throw new ConfigurationException("memtable_flush_writers must be at least 1, but was " + conf.memtable_flush_writers, false); if (conf.memtable_cleanup_threshold == null) + { conf.memtable_cleanup_threshold = (float) (1.0 / (1 + conf.memtable_flush_writers)); + } + else + { + logger.warn("memtable_cleanup_threshold has been deprecated and should be removed from cassandra.yaml"); + } if (conf.memtable_cleanup_threshold < 0.01f) throw new ConfigurationException("memtable_cleanup_threshold must be >= 0.01, but was " + conf.memtable_cleanup_threshold, false);
