Threadpool merge scheduler #120869
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Threadpool merge scheduler #120869
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This was referenced Jun 9, 2025
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This adds a new merge scheduler implementation that uses a (new) dedicated thread pool to run the merges. This way the number of concurrent merges is limited to the number of threads in the pool (i.e. the number of allocated processors to the ES JVM). It implements dynamic IO throttling (the same target IO rate for all merges, roughly, with caveats) that's adjusted based on the number of currently active (queued + running) merges. Smaller merges are always preferred to larger ones, irrespective of the index shard that they're coming from. The implementation also supports the per-shard "max thread count" and "max merge count" settings, the later being used today for indexing throttling. Note that IO throttling, max merge count, and max thread count work similarly, but not identical, to their siblings in the ConcurrentMergeScheduler. The per-shard merge statistics are not affected, and the thread-pool statistics should reflect the merge ones (i.e. the completed thread pool stats reflects the total number of merges, across shards, per node).
albertzaharovits
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…ep up with the merge load (elastic#125654) Fixes an issue where indexing throttling kicks in while disk IO is throttling. Instead disk IO should first unthrottle, and only then, if we still can't keep up with the merging load, start throttling indexing. Fixes elastic/elasticsearch-benchmarks#2437 Relates elastic#120869
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The intent here is to aim for fewer to-do merges enqueued for execution, and to unthrottle disk IO at a faster rate when the queue grows longer. Overall this results in less merge disk throttling. Relates elastic/elasticsearch-benchmarks#2437 elastic#120869
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This was referenced Jun 9, 2025
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…gMergeTasks (elastic#126058) Fixes elastic#125842 Relates elastic#120869
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…gMergeTasks (elastic#126058) Fixes elastic#125842 Relates elastic#120869
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This deprecates the `indices.merge.scheduler.use_thread_pool` setting that was introduced in #120869 because this setting should not normally be used, unless instructed so by engineering to get around temporary issues with the new threadpool-based merge scheduler.
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…9464) This deprecates the `indices.merge.scheduler.use_thread_pool` setting that was introduced in elastic#120869 because this setting should not normally be used, unless instructed so by engineering to get around temporary issues with the new threadpool-based merge scheduler.
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…9464) (#129628) * Deprecate indices.merge.scheduler.use_thread_pool setting (#129464) This deprecates the `indices.merge.scheduler.use_thread_pool` setting that was introduced in #120869 because this setting should not normally be used, unless instructed so by engineering to get around temporary issues with the new threadpool-based merge scheduler. * Update warning msg
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Jun 23, 2025
…9464) This deprecates the `indices.merge.scheduler.use_thread_pool` setting that was introduced in elastic#120869 because this setting should not normally be used, unless instructed so by engineering to get around temporary issues with the new threadpool-based merge scheduler.
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Jun 25, 2025
…9464) This deprecates the `indices.merge.scheduler.use_thread_pool` setting that was introduced in elastic#120869 because this setting should not normally be used, unless instructed so by engineering to get around temporary issues with the new threadpool-based merge scheduler.
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This documents the new threadpool-based merge scheduler, which is disk space aware, and blocks merges when disk space is low. The code changes were mostly introduced in elastic#120869 and elastic#127613 .
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This documents the new threadpool-based merge scheduler, which is disk space aware, and blocks merges when disk space is low. The code changes were mostly introduced in elastic#120869 and elastic#127613 .
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…k space aware, and blocks merges when disk space is low. The code changes were mostly introduced in elastic#120869 and elastic#127613 .
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This documents the new threadpool-based merge scheduler, which is disk space aware, and blocks merges when disk space is low. The code changes were mostly introduced in elastic#120869 and elastic#127613 .
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This adds a new merge scheduler implementation that uses a (new) dedicated thread pool to run the merges. This way the number of concurrent merges is limited to the number of threads in the pool (i.e. the number of allocated processors to the ES JVM).
It implements dynamic IO throttling (the same target IO rate for all merges, roughly, with caveats) that's adjusted based on the number of currently active (queued + running) merges.
Smaller merges are always preferred to larger ones, irrespective of the index shard that they're coming from.
The implementation also supports the per-shard "max thread count" and "max merge count" settings, the later being used today for indexing throttling.
Note that IO throttling, max merge count, and max thread count work similarly, but not identical, to their siblings in the
ConcurrentMergeScheduler.The per-shard merge statistics are not affected, and the thread-pool statistics should reflect the merge ones (i.e. the completed thread pool stats reflects the total number of merges, across shards, per node).