mirror of
https://github.com/scylladb/scylladb.git
synced 2026-06-07 07:23:15 +00:00
d980f550d1
fill_buffer() will keep scanning until _lower_bound_changed is true, even if preemption is signaled, so that the reader makes forward progress. Before the patch, we did not update _lower_bound on touching a dummy entry. The read will not respect preemption until we hit a non-dummy row. If there is a lot of dummy rows, that can cause reactor stalls. Fix that by updating _lower_bound on dummy entries as well. Refs #8153. Tested with perf_row_cache_reads: ``` $ build/release/test/perf/perf_row_cache_reads -c1 -m200M Rows in cache: 0 Populating with dummy rows Rows in cache: 373929 Scanning read: 183.658966 [ms], preemption: {count: 848, 99%: 0.545791 [ms], max: 0.519343 [ms]}, cache: 99/100 [MB] read: 120.951515 [ms], preemption: {count: 257, 99%: 0.545791 [ms], max: 0.518795 [ms]}, cache: 99/100 [MB] ``` Notice that max preemption latency is low in the second "read:" line. Closes #8167 * github.com:scylladb/scylla: row_cache: Make fill_buffer() preemptable when cursor leads with dummy rows tests: perf: Introduce perf_row_cache_reads row_cache: Add metric for dummy row hits