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 [EMAIL PROTECTED] | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 ---------------------------(end of broadcast)--------------------------- TIP 2: you can get off all lists at once with the unregister command (send "unregister YourEmailAddressHere" to [EMAIL PROTECTED])
