Re: INSERT...ON DUPLICATE KEY IGNORE

On Sat, Aug 31, 2013 at 7:53 PM, Peter Geoghegan <pg(at)heroku(dot)com> wrote:
> With a table with many unique indexes and many reasons to decide
> to reject a tuple proposed for insertion by INSERT...ON DUPLICATE KEY
> IGNORE, it isn't hard to imagine them all becoming heavily bloated
> very quickly.

There may be no index tuple directly corresponding to some heap tuple
where you might expect that, due to transactions aborting (as with a
traditional unique constraint violations) or because of HOT, but,
prior to now, never the other way around (heap tuples are created
first and physically killed last). That is an assumption that has
existed since the Berkeley days, and it is something that may be
treated as an invariant in some places. Autovacuum is one such place,
I'd say. Isn't it the case that the autovacuum launcher daemon might
not hear about all of this index-only bloat, even if it was extremely
serious? Isn't the threshold it follows only in respect of heap tuples
(even if the statistics collector does collect index tuple stats
separately)?

--
Peter Geoghegan