Re: Seqscan in MAX(index_column)

Christopher Browne wrote:
> Wouldn't this more or less be the same thing as having a trigger that
> does, upon each insert/delete "update pg_counts set count = count + 1
> where reltable = 45232;"? (... where 1 would be -1 for deletes, and where
> 45232 is the OID of the table...)
>
> Technically, it seems _feasible_, albeit with the problem that it
> turns pg_counts into a pretty horrid bottleneck. If lots of backends
> are updating that table, then row 45232 in pg_counts becomes
> troublesome because all those processes have to serialize around
> updating it.
>
> And if I have tables where I insert lots of data, but couldn't care
> less how many rows they have, this effort is wasted.
>
> When I was curious as to how COUNT might be maintained, I was pretty
> sure that this wouldn't be the preferred method...

See my later idea of the trigger doing +/-1 rather than locking the
value during the transaction.

If we don't do it this way, I can't think of another way that would
honor MVCC visibility.

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