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This patchset fixes reactor stalls caused by cache invalidation not being preemptible.
This becomes a problem when there is a lot of partitions in cache inside the invalidated range.
This affects high-level operations like nodetool refresh, table
truncation, repair and streaming.
Fixes#2683
The improvement on stalls was measured using tests/perf_row_cache_update:
Before:
Small partitions, no overwrites:
invalidation: 339.420624 [ms], preemption: {count: 2, 99%: 0.008239 [ms], max: 339.422144 [ms]}
Small partition with a few rows:
invalidation: 191.855331 [ms], preemption: {count: 2, 99%: 0.008239 [ms], max: 191.856816 [ms]}
Large partition, lots of small rows:
invalidation: 0.959328 [ms], preemption: {count: 2, 99%: 0.008239 [ms], max: 0.961453 [ms]}
After:
Small partitions, no overwrites:
invalidation: 400.505554 [ms], preemption: {count: 843, 99%: 0.545791 [ms], max: 0.502340 [ms]}
Small partition with a few rows:
invalidation: 306.352600 [ms], preemption: {count: 644, 99%: 0.545791 [ms], max: 0.506464 [ms]}
Large partition, lots of small rows:
invalidation: 0.963660 [ms], preemption: {count: 2, 99%: 0.009887 [ms], max: 0.963264 [ms]}
The maximum scheduling latency went down form 339 ms to 0.5 ms (task quota).
Tests:
- unit (dev)
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* tag 'cache-preemptible-invalidation-v2' of github.com:tgrabiec/scylla:
row_cache: Make invalidate() preemptible
row_cache: Switch _prev_snapshot_pos to be a ring_position_ext
dht: Introduce ring_position_ext
dht: ring_position_view: Take key by const pointer
tests: perf_row_cache_update: Rename 'stall' to 'preemption' to avoid confusion
tests: perf_row_cache_update: Report stalls around invalidation
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