Thread

Re: A problem with WAL

Vadim Mikheev <vmikheev@sectorbase.com> — 2001-08-30T20:25:56Z

> I've read the documentation for PostgreSQL 7.1.3 and I don't
> see how to tell when I can remove these:
> [root@dugite data]# ls pg_xlog/00000000000000* | wc -l
>     168
...
> 2001-08-29 04:48:34 [4946]   DEBUG:  Redo record at (0, 3099659748); 

3099659748 / (16*1024*1024) = 184 = 0xB8

so you can remove files with last two digits in 00 - B7 and restart
postmaster.

> Undo record at (0, 294566376); Shutdown FALSE
...
> 3) Performance - there's no (or insufficient) removal of old logs.

7.1.X takes UNDO record into account when deciding what logs can be
removed. It's not required currently because of UNDO operation is
not implemented, yet. I believe Tom made patch to consider only REDO
record and upcoming 7.2 is already updated.
Anyway, try to avoid transactions with huge write activity -
we'll probably implement UNDO in future and you'll not be able to
remove log files required to UNDO changes made by uncommitted
transactions.

Vadim