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Merge pull request #16971 from clintongormley/merge-settings-docs 

Redocument the `index.merge.scheduler.max_thread_count` setting
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Clinton Gormley 2016-03-07 10:42:26 +01:00
parent 54018a5d37 6d7e8814d6
commit a5eca17b4e
2 changed files with 36 additions and 0 deletions
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6
docs/reference/index-modules.asciidoc
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@ -148,6 +148,10 @@ Other index settings are available in index modules:
Enable or disable dynamic mapping for an index. Enable or disable dynamic mapping for an index.
<<index-modules-merge,Merging>>::
Control over how shards are merged by the background merge process.
<<index-modules-similarity,Similarities>>:: <<index-modules-similarity,Similarities>>::
Configure custom similarity settings to customize how search results are Configure custom similarity settings to customize how search results are
@ -173,6 +177,8 @@ include::index-modules/allocation.asciidoc[]
include::index-modules/mapper.asciidoc[] include::index-modules/mapper.asciidoc[]
include::index-modules/merge.asciidoc[]
include::index-modules/similarity.asciidoc[] include::index-modules/similarity.asciidoc[]
include::index-modules/slowlog.asciidoc[] include::index-modules/slowlog.asciidoc[]

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docs/reference/index-modules/merge.asciidoc Normal file
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@ -0,0 +1,30 @@
[[index-modules-merge]]
== Merge
A shard in elasticsearch is a Lucene index, and a Lucene index is broken down
into segments. Segments are internal storage elements in the index where the
index data is stored, and are immutable. Smaller segments are periodically
merged into larger segments to keep the index size at bay and to expunge
deletes.
The merge process uses auto-throttling to balance the use of hardware
resources between merging and other activities like search.
[float]
[[merge-scheduling]]
=== Merge scheduling
The merge scheduler (ConcurrentMergeScheduler) controls the execution of merge
operations when they are needed. Merges run in separate threads, and when the
maximum number of threads is reached, further merges will wait until a merge
thread becomes available.
The merge scheduler supports the following _dynamic_ setting:
`index.merge.scheduler.max_thread_count`::
The maximum number of threads that may be merging at once. Defaults to
`Math.max(1, Math.min(4, Runtime.getRuntime().availableProcessors() / 2))`
which works well for a good solid-state-disk (SSD). If your index is on
spinning platter drives instead, decrease this to 1.