feat: Add async data cache lock contention stats #16203
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…6203) Summary: New metrics added to monitor time spent waiting for shard mutexes: - `kMetricMemoryCacheNumShardMutexWaitClocks`: Total clocks waiting for shard mutexes. - `kMetricMemoryCacheShardMutexWaitTimeMs`: Milliseconds waited, based on ~3GHz CPU. Differential Revision: D92068037
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xiaoxmeng
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Feb 3, 2026
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@kewang1024 thanks for the change. Left some comments. Do we really need to count these stats?
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| // Clocks spent waiting to acquire shard mutexes, since last counter retrieval | ||
| DEFINE_METRIC( | ||
| kMetricMemoryCacheNumShardMutexWaitClocks, |
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can you update metrics.rst for the new metrics?
| kMetricMemoryCacheNumShardMutexWaitClocks, | ||
| facebook::velox::StatType::SUM); | ||
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| // Time in milliseconds spent waiting to acquire shard mutexes, since last |
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I think walltime is sufficient.
s/kMetricMemoryCacheShardMutexWaitTimeMs/kMetricMemoryCacheLockWaitTimeUs/?
| std::atomic<uint64_t> allocClocks_{0}; | ||
| // Tracker of cumulative clocks spent waiting to acquire shard mutex. | ||
| // Mutable to allow updating from const methods like exists(). | ||
| mutable std::atomic<uint64_t> shardMutexWaitClocks_{0}; |
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std::atomic_uint64_t shardLockWaitUs_
| /// lifetime for entries in cache. | ||
| int64_t sumEvictScore{0}; | ||
| /// Cumulative clocks spent waiting to acquire shard mutexes. | ||
| uint64_t shardMutexWaitClocks{0}; |
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s/shardMutexWaitClocks/shardLockWaitUs/
| public: | ||
| TimedLockGuard(std::mutex& mutex, std::atomic<uint64_t>& waitClocks) | ||
| : lock_(mutex, std::defer_lock) { | ||
| ClockTimer timer(waitClocks); |
| // Helper that uses ClockTimer to measure the lock acquisition time. | ||
| class TimedLockGuard { | ||
| public: | ||
| TimedLockGuard(std::mutex& mutex, std::atomic<uint64_t>& waitClocks) |
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Let's have a per-thread local counter for this? Like use ConcurrentCounter in velox/common/base/ConcurrentCounter.h?
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Summary:
New metrics added to monitor time spent waiting for shard mutexes:
kMetricMemoryCacheNumShardMutexWaitClocks: Total clocks waiting for shard mutexes.kMetricMemoryCacheShardMutexWaitTimeMs: Milliseconds waited, based on ~3GHz CPU.Differential Revision: D92068037