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Improve comment on top of pgstat_count_io_op_time()

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This commit adds more documentation to pgstat_count_io_op_time() in
pgstat_io.c, explaining its internals for pgstat_count_buffer_*(),
pgBufferUsage and the contexts where these are used.

Extracted from a larger patch by the same author.

Author: Nazir Bilal Yavuz
Discussion: https://postgr.es/m/CAN55FZ3AiQ+ZMxUuXnBpd0Rrh1YhwJ5FudkHg=JU0P+-W8T4Vg@mail.gmail.com
This commit is contained in:
Michael Paquier
2025-02-03 11:19:58 +09:00
parent fcce828529
commit b998fedab7
1 changed files with 8 additions and 0 deletions
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8
src/backend/utils/activity/pgstat_io.c
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@ -107,6 +107,14 @@ pgstat_prepare_io_time(bool track_io_guc)
/*
* Like pgstat_count_io_op() except it also accumulates time.
*
* The calls related to pgstat_count_buffer_*() are for pgstat_database. As
* pg_stat_database only counts block read and write times, these are done for
* IOOP_READ, IOOP_WRITE and IOOP_EXTEND.
*
* pgBufferUsage is used for EXPLAIN. pgBufferUsage has write and read stats
* for shared, local and temporary blocks. pg_stat_io does not track the
* activity of temporary blocks, so these are ignored here.
*/
void
pgstat_count_io_op_time(IOObject io_object, IOContext io_context, IOOp io_op,