Fix StopWatch bug; Remove setting record_read_stats

[hx235]

Context/Summary:

• StopWatch enable stats even when StatsLevel::kExceptTimers is set. It's a harmless bug though since reportTimeToHistogram() will not report it anyway according to https://github.com/facebook/rocksdb/blob/main/include/rocksdb/statistics.h#L705
• Group rocksdb.sst.read.micros stat by IOActivity flush and compaction #11288 should have removed logics of setting record_read_stats = !for_compaction as we don't differentiate RandomAccessFileReader's stats behavior based on compaction or not (instead we now report stats of different IO activities including compaction to different stats). Fixing this should report more compaction related file read micros that aren't reported previously due to for_compaction==true

Test:

• DB bench pre vs post fix with small max_open_files

Setup command
./db_ bench -db=/dev/shm/testdb/ -statistics=true -benchmarks=fillseq -key_size=32 -value_size=512 -num=5000 -write_buffer_size=655 -target_file_size_base=655 -disable_auto_compactions=true -compression_type=none -bloom_bits=3

Run command
./db_bench --open_files=1 -use_existing_db=true -db=/dev/shm/testdb2/ -statistics=true -benchmarks=compactall -key_size=32 -value_size=512 -num=5000 -write_buffer_size=655 -target_file_size_base=655 -disable_auto_compactions=true -compression_type=none -bloom_bits=3

Pre-fix

rocksdb.sst.read.micros P50 : 2.056175 P95 : 4.647739 P99 : 8.948475 P100 : 25.000000 COUNT : 4451 SUM : 12827
rocksdb.file.read.flush.micros P50 : 0.000000 P95 : 0.000000 P99 : 0.000000 P100 : 0.000000 COUNT : 0 SUM : 0
rocksdb.file.read.compaction.micros P50 : 2.057397 P95 : 4.625253 P99 : 8.749474 P100 : 25.000000 COUNT : 4382 SUM : 12608
rocksdb.file.read.db.open.micros P50 : 1.985294 P95 : 9.100000 P99 : 13.000000 P100 : 13.000000 COUNT : 69 SUM : 219

Post-fix (with a higher rocksdb.file.read.compaction.micros count)

rocksdb.sst.read.micros P50 : 1.858968 P95 : 3.653086 P99 : 5.968000 P100 : 21.000000 COUNT : 3548 SUM : 9119
rocksdb.file.read.flush.micros P50 : 0.000000 P95 : 0.000000 P99 : 0.000000 P100 : 0.000000 COUNT : 0 SUM : 0
rocksdb.file.read.compaction.micros P50 : 1.857027 P95 : 3.627614 P99 : 5.738621 P100 : 21.000000 COUNT : 3479 SUM : 8904
rocksdb.file.read.db.open.micros P50 : 2.000000 P95 : 6.733333 P99 : 11.000000 P100 : 11.000000 COUNT : 69 SUM : 215

• CI

[facebook-github-bot]

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[ajkr]

LGTM. I think we should remove "after #11444" from the title/description since the diff is based on code that does not include #11444. Also please update HISTORY.md to mention the SST_READ_MICROS scope expanded to all SST reads (some compaction reads were previously excluded).

[facebook-github-bot]

@hx235 has updated the pull request. You must reimport the pull request before landing.

[hx235]

@ajkr Fixed. I kept confusing 11444 with 11288!

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[facebook-github-bot]

@hx235 merged this pull request in dcc6fc9.