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db: optimize levelIter for non-matching bloom filter #1091
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Commits on Mar 19, 2021
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db: optimize levelIter for non-matching bloom filter
When SeekPrefixGE on the underlying file returns false due to a bloom filter non-match, levelIter would skip to the next file. This is wasteful if the upper bound of the file is beyond the prefix. Additionally, it defeats the optimization for sparse key spaces like CockroachDB's lock table, where we try to reuse the current position of the iterator -- by skipping to the next file the subsequent SeekPrefixGE will again need to reload the previous file. This behavior was first noticed when diagnosing tpcc slowness in CockroacbDB, where almost half the overhead of seeking in the lock table could be attributed to this (see cockroachdb/cockroach#62078 for details). The benchmark numbers for bloom=true/with-tombstone=false are the ones intended to benefit from this change. name old time/op new time/op delta IteratorSeqSeekPrefixGENotFound/skip=1/bloom=false/with-tombstone=false-16 441ns ± 9% 445ns ± 7% ~ (p=0.332 n=19+20) IteratorSeqSeekPrefixGENotFound/skip=1/bloom=false/with-tombstone=true-16 299ns ± 3% 300ns ± 3% ~ (p=0.455 n=20+20) IteratorSeqSeekPrefixGENotFound/skip=1/bloom=true/with-tombstone=false-16 3.73µs ± 8% 0.82µs ± 2% -78.02% (p=0.000 n=20+16) IteratorSeqSeekPrefixGENotFound/skip=1/bloom=true/with-tombstone=true-16 1.78µs ±73% 1.21µs ± 7% -32.15% (p=0.000 n=20+20) IteratorSeqSeekPrefixGENotFound/skip=2/bloom=false/with-tombstone=false-16 484ns ±27% 427ns ± 2% -11.83% (p=0.000 n=19+19) IteratorSeqSeekPrefixGENotFound/skip=2/bloom=false/with-tombstone=true-16 320ns ± 7% 300ns ± 3% -6.11% (p=0.000 n=16+19) IteratorSeqSeekPrefixGENotFound/skip=2/bloom=true/with-tombstone=false-16 5.07µs ±41% 0.82µs ± 2% -83.84% (p=0.000 n=20+18) IteratorSeqSeekPrefixGENotFound/skip=2/bloom=true/with-tombstone=true-16 1.76µs ±37% 1.21µs ± 9% -30.92% (p=0.000 n=20+20) IteratorSeqSeekPrefixGENotFound/skip=4/bloom=false/with-tombstone=false-16 439ns ± 4% 436ns ± 6% ~ (p=0.109 n=20+20) IteratorSeqSeekPrefixGENotFound/skip=4/bloom=false/with-tombstone=true-16 435ns ±29% 307ns ± 5% -29.40% (p=0.000 n=20+19) IteratorSeqSeekPrefixGENotFound/skip=4/bloom=true/with-tombstone=false-16 5.63µs ±19% 0.82µs ± 2% -85.40% (p=0.000 n=20+19) IteratorSeqSeekPrefixGENotFound/skip=4/bloom=true/with-tombstone=true-16 1.87µs ±36% 1.24µs ± 8% -33.66% (p=0.000 n=20+20) name old alloc/op new alloc/op delta IteratorSeqSeekPrefixGENotFound/skip=1/bloom=false/with-tombstone=false-16 0.00B 0.00B ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=1/bloom=false/with-tombstone=true-16 0.00B 0.00B ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=1/bloom=true/with-tombstone=false-16 0.00B 0.00B ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=1/bloom=true/with-tombstone=true-16 271B ± 0% 271B ± 0% ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=2/bloom=false/with-tombstone=false-16 0.00B 0.00B ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=2/bloom=false/with-tombstone=true-16 0.00B 0.00B ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=2/bloom=true/with-tombstone=false-16 0.00B 0.00B ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=2/bloom=true/with-tombstone=true-16 271B ± 0% 271B ± 0% ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=4/bloom=false/with-tombstone=false-16 0.00B 0.00B ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=4/bloom=false/with-tombstone=true-16 0.00B 0.00B ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=4/bloom=true/with-tombstone=false-16 0.00B 0.00B ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=4/bloom=true/with-tombstone=true-16 271B ± 0% 271B ± 0% ~ (all equal) name old allocs/op new allocs/op delta IteratorSeqSeekPrefixGENotFound/skip=1/bloom=false/with-tombstone=false-16 0.00 0.00 ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=1/bloom=false/with-tombstone=true-16 0.00 0.00 ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=1/bloom=true/with-tombstone=false-16 0.00 0.00 ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=1/bloom=true/with-tombstone=true-16 1.00 ± 0% 1.00 ± 0% ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=2/bloom=false/with-tombstone=false-16 0.00 0.00 ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=2/bloom=false/with-tombstone=true-16 0.00 0.00 ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=2/bloom=true/with-tombstone=false-16 0.00 0.00 ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=2/bloom=true/with-tombstone=true-16 1.00 ± 0% 1.00 ± 0% ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=4/bloom=false/with-tombstone=false-16 0.00 0.00 ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=4/bloom=false/with-tombstone=true-16 0.00 0.00 ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=4/bloom=true/with-tombstone=false-16 0.00 0.00 ~ (all equal) IteratorSeqSeekPrefixGENotFound/skip=4/bloom=true/with-tombstone=true-16 1.00 ± 0% 1.00 ± 0% ~ (all equal)
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