> Matthew Kirkwood <matthew@hairy.beasts.org> writes:
> > From some stracing of 7.1, the most common syscall issued by
> > postgres is an lseek() to the end of the file, presumably to
> > find its length, which seems to happen up to about a dozen
> > times per (pgbench) transaction.
>
> > Tablespaces would solve this (not that lseek is a particularly
> > expensive operation, of course).
>
> No, they wouldn't; or at least they'd just create a different problem.
> The reason for the lseek is that the file length may have changed since
> the current backend last checked it. To avoid lseek we'd need some
> shared data structure that maintains the current length of every active
> table, which would be a nuisance to maintain and probably a source of
> contention delays.
Seems we should cache the file lengths somehow. Not sure how to do it
because our file system cache is local to each backend.
> (Of course, such a data structure would just be the tip of the iceberg
> of what we'd have to maintain for ourselves if we couldn't depend on the
> kernel to do it for us. Reimplementing a filesystem doesn't strike me
> as a profitable use of our time.)
Ditto. The database is complicated enough.
-- 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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