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storage: clean up MVCC key encoding functions #75721

Merged
merged 3 commits into from
Feb 1, 2022
Merged

storage: clean up MVCC key encoding functions #75721

merged 3 commits into from
Feb 1, 2022

Commits on Feb 1, 2022

  1. storage: move MVCC key/encoding logic into separate file 

    This splits MVCC keys and their encoding into a separate file, following
the same convention as `engine_key.go`. There is additional decoding
logic in `enginepb/decode.go` which has not been moved -- this was
originally to avoid a RocksDB CGo dependency for these functions, but
Pebble still has a (tiny) CGo dependency so we leave them for now.

Release note: None
    @erikgrinaker
    erikgrinaker committed Feb 1, 2022
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  2. storage: include MVCC in names of key encoding functions 

    Release note: None
    @erikgrinaker
    erikgrinaker committed Feb 1, 2022
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  3. storage: clean up MVCC key encoding functions 

    In particular, this separates the timestamp encoding from the overall
key encoding. This is necessary for the MVCC range tombstone work, where
Pebble key suffixes (timestamps) are processed in isolation.

Unfortunately, this adds ~9% overhead for `EncodeMVCCKey()`. This was
found to be due to additional function call overhead, and the Go
compiler's unwillingness to inline these. This was considered acceptable
for the encode path, while with the hotter `DecodeMVCCKey()` path the
timestamp decoding logic was instead duplicated to avoid this overhead.

```
name                                            old time/op    new time/op    delta
EncodeMVCCKey/key=empty/ts=empty-24               15.8ns ± 0%    15.7ns ± 0%   -0.46%  (p=0.000 n=10+10)
EncodeMVCCKey/key=empty/ts=walltime-24            17.9ns ± 0%    19.5ns ± 0%   +8.88%  (p=0.000 n=10+10)
EncodeMVCCKey/key=empty/ts=walltime+logical-24    18.5ns ± 0%    20.1ns ± 0%   +8.99%  (p=0.000 n=10+10)
EncodeMVCCKey/key=empty/ts=all-24                 18.8ns ± 0%    20.4ns ± 0%   +8.66%  (p=0.000 n=10+10)
EncodeMVCCKey/key=short/ts=walltime+logical-24    19.1ns ± 0%    20.7ns ± 0%   +8.38%  (p=0.000 n=10+9)
EncodeMVCCKey/key=short/ts=all-24                 19.5ns ± 0%    20.7ns ± 0%   +6.18%  (p=0.000 n=10+9)
EncodeMVCCKey/key=short/ts=empty-24               16.3ns ± 0%    16.0ns ± 0%   -1.86%  (p=0.000 n=10+10)
EncodeMVCCKey/key=short/ts=walltime-24            18.1ns ± 0%    20.6ns ± 0%  +13.41%  (p=0.000 n=8+8)
EncodeMVCCKey/key=long/ts=empty-24                58.7ns ± 0%    58.8ns ± 0%   +0.15%  (p=0.000 n=10+10)
EncodeMVCCKey/key=long/ts=walltime-24             59.8ns ± 0%    60.8ns ± 0%   +1.78%  (p=0.000 n=10+9)
EncodeMVCCKey/key=long/ts=walltime+logical-24     60.7ns ± 0%    61.7ns ± 0%   +1.54%  (p=0.000 n=10+10)
EncodeMVCCKey/key=long/ts=all-24                  60.9ns ± 0%    61.9ns ± 0%   +1.60%  (p=0.000 n=10+9)
DecodeMVCCKey/key=empty/ts=empty-24               12.4ns ± 0%    12.4ns ± 0%     ~     (p=0.912 n=10+6)
DecodeMVCCKey/key=empty/ts=walltime-24            13.3ns ± 0%    13.3ns ± 0%     ~     (p=0.054 n=10+10)
DecodeMVCCKey/key=empty/ts=walltime+logical-24    13.3ns ± 0%    13.3ns ± 0%   -0.06%  (p=0.034 n=10+10)
DecodeMVCCKey/key=empty/ts=all-24                 13.6ns ± 0%    13.6ns ± 0%     ~     (p=0.509 n=10+10)
DecodeMVCCKey/key=short/ts=walltime+logical-24    13.3ns ± 0%    13.3ns ± 0%     ~     (all equal)
DecodeMVCCKey/key=short/ts=all-24                 13.6ns ± 0%    13.6ns ± 0%     ~     (p=0.151 n=10+10)
DecodeMVCCKey/key=short/ts=empty-24               12.5ns ± 0%    12.4ns ± 0%   -0.21%  (p=0.000 n=10+10)
DecodeMVCCKey/key=short/ts=walltime-24            13.3ns ± 0%    13.3ns ± 0%     ~     (p=0.577 n=8+10)
DecodeMVCCKey/key=long/ts=walltime+logical-24     13.3ns ± 0%    13.3ns ± 0%     ~     (all equal)
DecodeMVCCKey/key=long/ts=all-24                  13.6ns ± 0%    13.6ns ± 0%     ~     (p=0.650 n=10+10)
DecodeMVCCKey/key=long/ts=empty-24                12.4ns ± 0%    12.4ns ± 0%   +0.15%  (p=0.004 n=10+10)
DecodeMVCCKey/key=long/ts=walltime-24             13.3ns ± 0%    13.3ns ± 0%   +0.10%  (p=0.012 n=10+9)
```

Release note: None
    @erikgrinaker
    erikgrinaker committed Feb 1, 2022
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