Tom Lane wrote: > > Doug McNaught <[EMAIL PROTECTED]> writes: > > "Dann Corbit" <[EMAIL PROTECTED]> writes: > >> It would be nice if total table cardinality could be maintained live. > > > How would this work with MVCC? > > It wouldn't. That's why it's not there. Under MVCC, table cardinality > is in the eye of the beholder...
This is true, absolutely, but keeping a running total of the number of records should not change this fact. It may even make it more accurate. If count() comes back immediately with *a* number, that number was only accurate at the time of the transaction. If count() does a full table scan, it still only comes back with something accurate to the time of the transaction, but it could be more likely less accurate on a busy/large table because many more things may have changed during the time used by a full table scan. The issue of a busy table shouldn't make a difference either. If we aready accept that count() returns the known count at the beginning time of the transaction, and not the count() at the end of a tansaction (MVCC), then taking a count() from a counter which is updated when delete/inserts are performed just as accurate, or at least just as subject to inaccuracies. ---------------------------(end of broadcast)--------------------------- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
