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scheduler can read locks by rocksdb cursor #18208

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#18200
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scheduler can read locks by rocksdb cursor#18208
#18200
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type/enhancementThe issue or PR belongs to an enhancement.
@you06

Description

@you06
you06
opened on Feb 12, 2025

Development Task

When handling commit and resolve_lock operations, TiKV reads the related locks before writing. The read is performed through multiple individual get operations, which results in numerous slow seek operations in RocksDB. Below is a CPU profile and resolve-lock scheduler metrics during the lock resolution period.

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The root cause of this behavior is that the reader is not running in scan mode (self.lock_cursor is none). So the near_seek operation doesn't work.

tikv/src/storage/mvcc/reader/reader.rs

Lines 243 to 254 in caf82d2

let res = if let Some(ref mut cursor) = self.lock_cursor {
match cursor.get(key, &mut self.statistics.lock)? {
Some(v) => Some(Lock::parse(v)?),
None => None,
}
} else {
self.statistics.lock.get += 1;
match self.snapshot.get_cf(CF_LOCK, key)? {
Some(v) => Some(Lock::parse(&v)?),
None => None,
}
};

Usages need to be optimized

tikv/src/storage/txn/commands/resolve_lock.rs

Lines 86 to 89 in caf82d2

let mut reader = ReaderWithStats::new(
SnapshotReader::new_with_ctx(TimeStamp::zero(), snapshot, &ctx),
context.statistics,
);

tikv/src/storage/txn/commands/commit.rs

Lines 58 to 61 in caf82d2

let mut reader = ReaderWithStats::new(
SnapshotReader::new_with_ctx(self.lock_ts, snapshot, &self.ctx),
context.statistics,
);

tikv/src/storage/txn/commands/prewrite.rs

Lines 540 to 543 in caf82d2

let mut reader = ReaderWithStats::new(
SnapshotReader::new_with_ctx(self.start_ts, snapshot, &self.ctx),
context.statistics,
);

tikv/src/storage/txn/commands/rollback.rs

Lines 53 to 56 in f0fc694

let mut reader = ReaderWithStats::new(
SnapshotReader::new_with_ctx(self.start_ts, snapshot, &self.ctx),
context.statistics,
);

tikv/src/storage/txn/commands/acquire_pessimistic_lock.rs

Lines 91 to 94 in f0fc694

let mut reader = ReaderWithStats::new(
SnapshotReader::new_with_ctx(start_ts, snapshot, &ctx),
context.statistics,
);

tikv/src/storage/txn/commands/check_secondary_locks.rs

Lines 155 to 158 in f0fc694

let mut reader = ReaderWithStats::new(
SnapshotReader::new_with_ctx(self.start_ts, snapshot, &self.ctx),
context.statistics,
);

tikv/src/storage/txn/commands/flush.rs

Lines 79 to 82 in f0fc694

let mut reader = ReaderWithStats::new(
SnapshotReader::new_with_ctx(self.start_ts, snapshot, &self.ctx),
context.statistics,
);

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