Neil Conway wrote:
> On Thu, 2003-09-04 at 22:02, Bruce Momjian wrote:
> > My idea is that if a transaction doing a COUNT(*) would first look to
> > see if there already was a visible cached value, and if not, it would do
> > the COUNT(*) and insert into the cache table. Any INSERT/DELETE would
> > remove the value from the cache. As I see it, the commit of the
> > INSERT/DELETE transaction would then auto-invalidate the cache at the
> > exact time the transaction commits. This would allow MVCC visibility of
> > the counts.
>
> But this means that some of the time (indeed, *much* of the time),
> COUNT(*) would require a seqscan of the entire table. Since at many
> sites that will take an enormous amount of time (and disk I/O), that
> makes this solution infeasible IMHO.
>
> In general, I don't think this is worth doing.
It is possible it isn't worth doing. Can the INSERT/DELETE
incrementing/decrementing the cached count work reliabily?
-- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610)
359-1001+ If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square,
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