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Improve comments in slru.{c,h} about segment name format

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slru.h described incorrectly how SLRU segment names are formatted
depending on the segment number and if long or short segment names are
used.  This commit closes the gap with a better description, fitting
with the reality.

Reported-by: Noah Misch
Author: Aleksander Alekseev
Discussion: https://postgr.es/m/20240626002747.dc.nmisch@google.com
Backpatch-through: 17
This commit is contained in:
Michael Paquier 2024-07-23 16:54:51 +09:00
parent 65504b747f
commit ffb0603929
2 changed files with 18 additions and 4 deletions
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15
src/backend/access/transam/slru.c
View File

@ -72,6 +72,21 @@
#include "storage/shmem.h"
#include "utils/guc_hooks.h"
/*
* Converts segment number to the filename of the segment.
*
* "path" should point to a buffer at least MAXPGPATH characters long.
*
* If ctl->long_segment_names is true, segno can be in the range [0, 2^60-1].
* The resulting file name is made of 15 characters, e.g. dir/123456789ABCDEF.
*
* If ctl->long_segment_names is false, segno can be in the range [0, 2^24-1].
* The resulting file name is made of 4 to 6 characters, as of:
*
* dir/1234 for [0, 2^16-1]
* dir/12345 for [2^16, 2^20-1]
* dir/123456 for [2^20, 2^24-1]
*/
static inline int
SlruFileName(SlruCtl ctl, char *path, int64 segno)
{

7
src/include/access/slru.h
View File

@ -134,10 +134,9 @@ typedef struct SlruCtlData
bits16 bank_mask;
/*
* If true, use long segment filenames formed from lower 48 bits of the
* segment number, e.g. pg_xact/000000001234. Otherwise, use short
* filenames formed from lower 16 bits of the segment number e.g.
* pg_xact/1234.
* If true, use long segment file names. Otherwise, use short file names.
*
* For details about the file name format, see SlruFileName().
*/
bool long_segment_names;