perf: pool []queryValues slices to reduce per-request allocations

[mykaul]

Use bucketed sync.Pool (caps 8/16/32/64/128) to reuse []queryValues slices in executeQuery() and executeBatch(). Slices are returned to the pool immediately after c.exec() serializes the frame, with clear() to release string/[]byte references.

Benchmark Results
Benchmark Pool make() Speedup Alloc savings
Sequential (8 values) ~53 ns/op, 27 B ~132 ns/op, 387 B ~2.5x 360 B/op
Parallel (8 values) ~31 ns/op, 27 B ~180 ns/op, 387 B ~5.8x 360 B/op

[mykaul]

CI failure is a transient issue, will send a separate fix.

[mykaul]

CI failure is a transient issue, will send a separate fix.

#766

[Copilot]

Pull request overview

This PR reduces per-request allocations in the query execution path by pooling []queryValues slices (bucketed by common sizes) and reusing them across executeQuery() and executeBatch() calls.

Changes:

• Add bucketed sync.Pool helpers for []queryValues allocation/reuse (caps 8/16/32/64/128).
• Use the pool in Conn.executeQuery() / Conn.executeBatch() and return slices after request frame serialization.
• Add unit tests and benchmarks covering bucket selection, pooling behavior, and allocation improvements.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
frame.go	Introduces the bucketed []queryValues pooling helpers (getQueryValues/putQueryValues/putBatchQueryValues).
conn.go	Switches query/batch execution to allocate params.values / b.values via the pool and returns them after frame serialization (plus cleanup on errors).
frame_test.go	Adds tests for bucket sizing and pooling behavior, plus benchmarks comparing pooled vs make() allocations.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

[mykaul]

Addressed the review feedback:

Fixed (this push):

• Clarified the misleading comments in conn.go (lines 1575 and 1799). Changed "no longer needed after c.exec() serialized the frame" → "values were consumed during frame serialization inside c.exec()". The original wording implied c.exec() only serializes, but it also sends; the key point is that the values slice has been fully read by that point and is safe to return to the pool.

Not a bug (Copilot false positive):

• The claim that s[:cap(s)] in getQueryValues will panic is factually wrong. Go allows reslicing up to the capacity of the original slice — this is a well-defined language feature, not a bug.

Acknowledged but not changing:

• The suggestion to defer pool returns to after error checking is a style preference. The current placement is correct: values are consumed during c.exec(), so returning them immediately after (before checking the error) is safe and keeps the pool return close to the consumption point.