perf: optimize time series memtable ingestion

[waynexia]

Signed-off-by: Ruihang Xia waynestxia@gmail.comI hereby agree to the terms of the GreptimeDB CLA.

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What's changed and what's your intention?

Some tiny optimizations for time series memtable (~5% improvement).

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Please convert it to a draft if some of the following conditions are not met.

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
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• API changes are backward compatible.
• Schema or data changes are backward compatible.

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[yihong0618]

learned how to perf from this, thank you very much

[evenyag]

@v0y4g3r PTAL

[v0y4g3r]

LGTM

[evenyag]

Others LGTM

[evenyag]

Looks like we should use BUILDER_CAPACITY as the capacity of freeze. We may update the capacity in freeze().

greptimedb/src/mito2/src/memtable/time_series.rs

Lines 640 to 647 in 5b6279f

	/// Freezes the active part and push it to `frozen`.
	fn freeze(&mut self, region_metadata: &RegionMetadataRef) {
	if self.active.len() != 0 {
	let mut builder = ValueBuilder::new(region_metadata, INITIAL_BUILDER_CAPACITY);
	std::mem::swap(&mut self.active, &mut builder);
	self.frozen.push(Values::from(builder));
	}
	}