Hi All,
pg_walfile_name() returns the WAL file name corresponding to the given
WAL location. Per
https://www.postgresql.org/docs/14/functions-admin.html
---
pg_walfile_name ( lsn pg_lsn ) → text
Converts a write-ahead log location to the name of the WAL file
holding that location.
---
The function uses XLByteToPrevSeg() which gives the name of previous
WAL file if the location falls on the boundary of WAL segment. I find
it misleading since the given LSN will fall into the segment provided
by XLByteToSeg() and not XLBytePrevSeg().
And it gives some surprising results as well
---
#select pg_walfile_name('0/0'::pg_lsn);
pg_walfile_name
--------------------------
00000001FFFFFFFF000000FF
(1 row)
----
Comment in the code says
---
/*
* Compute an xlog file name given a WAL location,
* such as is returned by pg_stop_backup() or pg_switch_wal().
*/
Datum
pg_walfile_name(PG_FUNCTION_ARGS)
---
XLByteToPrevSeg() may be inline with the comment but I don't think
that's what is conveyed by the documentation at least.
--
Best Wishes,
Ashutosh
