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bc1c92fd05
`flat_mutation_reader::consume_pausable` is widely used in Scylla. Some places worth mentioning are memtables and combined readers but there are others as well. This patchset improves `consume_pausable` in three ways: 1. it removes unnecessary allocation 2. it rearranges ifs to not check the same thing twice 3. for a consumer that returns plain stop_iteration not a future<stop_iteration> it reduces the amount of future usage Test: unit(dev, release, debug) Combined reader microbenchmark has shown from 2% to 22% improvement in median execution time while memtable microbenchmark has shown from 3.6% to 7.8% improvement in median execution time. Before the change: ``` ./build/release/test/perf/perf_mutation_readers --random-seed 3549335083 single run iterations: 0 single run duration: 1.000s number of runs: 5 number of cores: 16 random seed: 3549335083 test iterations median mad min max combined.one_row 1316234 140.120ns 0.020ns 140.074ns 140.141ns combined.single_active 7332 91.484us 31.890ns 91.453us 91.778us combined.many_overlapping 945 870.973us 429.720ns 868.625us 871.403us combined.disjoint_interleaved 7102 85.989us 7.847ns 85.973us 85.997us combined.disjoint_ranges 7129 85.570us 7.840ns 85.562us 85.596us combined.overlapping_partitions_disjoint_rows 5458 124.787us 56.738ns 124.731us 125.370us clustering_combined.ranges_generic 1920688 217.940ns 0.184ns 217.742ns 218.275ns clustering_combined.ranges_specialized 1935318 194.610ns 0.199ns 194.210ns 195.228ns memtable.one_partition_one_row 624001 1.600us 1.405ns 1.599us 1.605us memtable.one_partition_many_rows 79551 12.555us 1.829ns 12.549us 12.558us memtable.many_partitions_one_row 40557 24.748us 77.083ns 24.644us 25.135us memtable.many_partitions_many_rows 3220 310.429us 57.628ns 310.295us 311.189us ``` After the change: ``` ./build/release/test/perf/perf_mutation_readers --random-seed 3549335083 single run iterations: 0 single run duration: 1.000s number of runs: 5 number of cores: 16 random seed: 3549335083 test iterations median mad min max combined.one_row 1358839 109.222ns 0.122ns 109.089ns 109.348ns combined.single_active 7525 87.305us 25.540ns 87.273us 87.362us combined.many_overlapping 962 853.195us 1.904us 851.244us 855.142us combined.disjoint_interleaved 7310 81.988us 28.877ns 81.949us 82.032us combined.disjoint_ranges 7315 81.699us 37.144ns 81.662us 81.874us combined.overlapping_partitions_disjoint_rows 5591 120.964us 15.294ns 120.949us 121.120us clustering_combined.ranges_generic 1954722 211.993ns 0.052ns 211.883ns 212.084ns clustering_combined.ranges_specialized 2042194 187.807ns 0.066ns 187.732ns 188.289ns memtable.one_partition_one_row 648701 1.542us 0.339ns 1.542us 1.543us memtable.one_partition_many_rows 85007 11.759us 1.168ns 11.752us 11.782us memtable.many_partitions_one_row 43893 22.805us 17.147ns 22.782us 22.843us memtable.many_partitions_many_rows 3441 290.220us 41.720ns 290.172us 290.306us ``` Closes #8359 * github.com:scylladb/scylla: flat_mutation_reader: optimize consume_pausable for some consumers flat_mutation_reader: special case consumers in consume_pausable flat_mutation_reader: Change order of checks in consume_pausable flat_mutation_reader: fix indentation in consume_pausable flat_mutation_reader: Remove allocation in consume_pausable perf: Add benchmarks for large partitions