Tom Lane wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > question is if we do a big transaction that needs 10 log segments, do we
> > force an early CHECKPOINT to clear out the WAL segments or do we just
> > wait for the proper interval?
>
> A checkpoint is forced after every CHECKPOINT_SEGMENTS log segments,
> regardless of longevity of transactions. See
> http://developer.postgresql.org/docs/postgres/wal-configuration.html
>
> Since segments before the checkpoint-before-last are deleted or recycled
> after each checkpoint, the maximum number of back segments would
> normally be 2 * CHECKPOINT_SEGMENTS. We also pre-create WAL_FILES
> future log segments. Counting the current segment gives a total of
> WAL_FILES + 2 * CHECKPOINT_SEGMENTS + 1 log segments.
>
> AFAICS, the only way to force the current code into creating more than
> WAL_FILES + 2 * CHECKPOINT_SEGMENTS + 1 log segments is to be generating
> WAL entries at such a high rate that more than WAL_FILES log segments
> are filled before a triggered checkpoint can be completed.
>
Very interesting. Thanks. Is there a reason someone would manually run
the CHECKPOINT command?
-- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610)
853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill,
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