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079e77ff9e
Summary: I suspect LRUCache could use some optimization, and to support such an effort, a good benchmarking tool is needed. The existing cache_bench was heavily skewed toward insertion and lookup misses, and did not saturate memory with other work. This change should improve those things to better resemble a real workload. (All below using clang compiler, for some consistency, but not necessarily same version and settings.) The real workload is from production MySQL on RocksDB, filtering stacks containing "LRU", "ShardedCache" or "CacheShard." Lookup inclusive: 66% Insert inclusive: 17% Release inclusive: 15% An alternate simulated workload is MySQL running a LinkBench read test: Lookup inclusive: 54% Insert inclusive: 24% Release inclusive: 21% cache_bench default settings, prior to this change: Lookup inclusive: 35.8% Insert inclusive: 63.6% Release inclusive: 0% cache_bench after this change (intended as somewhat "tighter" workload than average production, more like LinkBench): Lookup inclusive: 52% Insert inclusive: 20% Release inclusive: 26% And top exclusive stacks (portion of stack samples as filtered above): Production MySQL: LRUHandleTable::FindPointer: 25.3% rocksdb::operator==: 15.1% <-- Slice == LRUCacheShard::LRU_Remove: 13.8% ShardedCache::Lookup: 8.9% __pthread_mutex_lock: 7.1% LRUCacheShard::LRU_Insert: 6.3% MurmurHash64A: 4.8% <-- Since upgraded to XXH3p ... Old cache_bench: LRUHandleTable::FindPointer: 23.6% __pthread_mutex_lock: 15.0% __pthread_mutex_unlock_usercnt: 11.7% __lll_lock_wait: 8.6% __lll_unlock_wake: 6.8% LRUCacheShard::LRU_Insert: 6.0% ShardedCache::Lookup: 4.4% LRUCacheShard::LRU_Remove: 2.8% ... rocksdb::operator==: 0.2% <-- Slice == ... New cache_bench: LRUHandleTable::FindPointer: 22.8% __pthread_mutex_unlock_usercnt: 14.3% rocksdb::operator==: 10.5% <-- Slice == LRUCacheShard::LRU_Insert: 9.0% __pthread_mutex_lock: 5.9% LRUCacheShard::LRU_Remove: 5.0% ... ShardedCache::Lookup: 2.9% ... So there's a bit more lock contention in the benchmark than in production, but otherwise looks similar enough to me. At least it's a big improvement over the existing code. Pull Request resolved: https://github.com/facebook/rocksdb/pull/6629 Test Plan: No production code changes, ran cache_bench with ASAN Reviewed By: ltamasi Differential Revision: D20824318 Pulled By: pdillinger fbshipit-source-id: 6f8dc5891ead0f87edbed3a615ecd5289d9abe12 |
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|---|---|---|
| .. | ||
| cache_bench.cc | ||
| cache_test.cc | ||
| clock_cache.cc | ||
| clock_cache.h | ||
| lru_cache.cc | ||
| lru_cache.h | ||
| lru_cache_test.cc | ||
| sharded_cache.cc | ||
| sharded_cache.h | ||