Limit batch_max to queue_capacity

[serprex]

This avoids wasting memory when reserving vector

Also update docs with new defaults

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Project	Status	Preview	Updated (UTC)
pg_stat_ch	🟢 Ready	View Preview	Aug 30, 2026, 3:31 AM

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[Copilot]

Pull request overview

This PR tightens the bgworker export batching logic by clamping pg_stat_ch.batch_max to the shared-memory queue’s capacity, and reduces unnecessary memory reservation when building the dequeue vector. It also updates defaults and documentation to match the new behavior.

Changes:

• Add PschEffectiveBatchMax() (batch_max clamped to queue capacity) and use it in the bgworker drain loop and exporter.
• Add PschQueueDepth() and use it as a sizing hint to avoid reserving an oversized std::vector when the queue is mostly empty.
• Update GUC defaults and documentation (README + reference docs) for new defaults and clamping behavior.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/worker/bgworker.c	Uses effective (clamped) batch max in the drain-loop “partial batch” termination check.
src/queue/shmem.h	Exposes new queue sizing/clamping helpers.
src/queue/shmem.c	Implements PschQueueDepth() and PschEffectiveBatchMax().
src/export/stats_exporter.cc	Reserves dequeue vector based on current queue depth; uses clamped batch max for export.
src/config/guc.c	Updates pg_stat_ch.batch_max default and documents clamping in the GUC description.
README.md	Updates documented defaults for queue capacity, flush interval, and batch max.
docs/reference/troubleshooting.mdx	Updates tuning guidance to reflect batch_max clamping.
docs/reference/configuration.mdx	Updates queue sizing/memory guidance and documents batch_max clamping behavior.

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[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated no new comments.

[JoshDreamland]