mirror of https://github.com/facebook/rocksdb.git
8e29f243c9
Summary: This occasional filesystem read in the write path has caused user pain. It doesn't seem very useful considering it only limits one component's merge chain length, and only helps merge uncached (i.e., infrequently read) values. This PR proposes allowing `max_successive_merges` to be exceeded when the value cannot be read from in-memory components. I included a rollback flag (`strict_max_successive_merges`) just in case. Pull Request resolved: https://github.com/facebook/rocksdb/pull/12365 Test Plan: "rocksdb.block.cache.data.add" is number of data blocks read from filesystem. Since the benchmark is write-only, compaction is disabled, and flush doesn't read data blocks, any nonzero value means the user write issued the read. ``` $ for s in false true; do echo -n "strict_max_successive_merges=$s: " && ./db_bench -value_size=64 -write_buffer_size=131072 -writes=128 -num=1 -benchmarks=mergerandom,flush,mergerandom -merge_operator=stringappend -disable_auto_compactions=true -compression_type=none -strict_max_successive_merges=$s -max_successive_merges=100 -statistics=true |& grep 'block.cache.data.add COUNT' ; done strict_max_successive_merges=false: rocksdb.block.cache.data.add COUNT : 0 strict_max_successive_merges=true: rocksdb.block.cache.data.add COUNT : 1 ``` Reviewed By: hx235 Differential Revision: D53982520 Pulled By: ajkr fbshipit-source-id: e40f761a60bd601f232417ac0058e4a33ee9c0f4 |
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| max_successive_merges_io.md | ||