Tom Lane wrote:
> Bruce Momjian <[EMAIL PROTECTED]> writes:
> > We do have a TODO item:
> >     * Consider using MVCC to cache count(*) queries with no WHERE clause
> > The idea is to cache a recent count of the table, then have
> > insert/delete add +/- records to the count.  A COUNT(*) would get the
> > main cached record plus any visible +/- records.  This would allow the
> > count to return the proper value depending on the visibility of the
> > requesting transaction, and it would require _no_ heap or index scan.
> ... and it would give the wrong answers.  Unless the cache is somehow
> snapshot-aware, so that it can know which other transactions should be
> included in your count.

The cache is an ordinary table, with xid's on every row.  I meant it
would require no index/heap scans of the large table --- it would still
require a scan of the "count" table.

  Bruce Momjian                        |
  [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])

Reply via email to