Ynt: WAL and backup recovery

Tom Lane <tgl@sss.pgh.pa.us> wrote in message
news:14951.990634138@sss.pgh.pa.us...
> Dario Brignardello <dbrignar@sinectis.com> writes:
> >       checkpoint_segments = 1
> > checkpoint_timeout = 30
>
> Reducing checkpoint_segments and checkpoint_timeout is actually
> seriously counterproductive, if your problem is amount of disk space
> chewed up by WAL logs during a long transaction (such as bulk load of
> a big table).  The WAL log cannot be truncated until the xact commits,
> so the checkpoints that happen meanwhile just cause log bloat.  Lots
> of it, because each checkpoint causes fresh copying of modified pages
> into the WAL log.
So let me know one thing, does checkpoint cause copying modified pages to
WAL log or does it just flush the modified pages to disk?
I thought WAL writings occur when pages being modified, deleted or inserted,
please correct me if I am wrong...thanx....


Murat



>
> Try increasing those numbers, not decreasing them.  Maybe 10/600 or so?
>
> Also, if you are short on disk space for WAL, increasing wal_files isn't
> such a great idea either.
>
> regards, tom lane
>
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