Marc G. Fournier wrote:
> On Sat, 14 Aug 2004, Bruce Momjian wrote:
>
> > Marc G. Fournier wrote:
> >> On Sat, 14 Aug 2004, Tom Lane wrote:
> >>
> >>> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> >>>> Many databases offer this feature. The submitter asked for it,
> >>>
> >>> Actually he didn't --- AFAICS you misinterpreted the thread completely.
> >>> The original suggestion was that we might be able to exploit a
> >>> transactional filesystem to improve performance *without* sacrificing
> >>> any correctness guarantees. Delayed fsync has nothing to do with that.
> >>>
> >>> (I'm dubious whether there's any performance improvement to be had that
> >>> would be worth the code uglification involved, since we're surely not
> >>> going to *require* a transactional filesystem and so two very different
> >>> code paths seem to be needed. But it's at least something to think about.)
> >>
> >> Just to expand on the 'dubiousness' ... remember awhile back when I worked
> >> through the 'no-WAL' version of PostgreSQL to test loading a database with
> >> WAL disabled? The performance improvements on loading a database weren't
> >> enough, I seem to recall, to warrant getting rid of WAL altogether ... so
> >> I can't see 'delayed WAL' being faster then 'no WAL' ...
> >
> > Uh, you mean fsync isn't a performance hit as it once was?
>
> No, I mean that writing WAL doesn't appear to be a performance hit ...
> removing WAL writing and doing a large db load, the load is a bit faster,
> but not as big as one would hope ...
OK. My idea is to remove fsync (poorly named) and add a new parameter
called transaction_loss. It would specify the number of seconds or
milliseconds before an abrupt server restart that you were willing to
lose transactions. The default would be zero (no loss), and we can
support -1 for the same as fsync off. Positive values would delay WAL
write/fsync for that many seconds/milliseconds.
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 359-1001
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