>>>>> "Amit" == Amit Kapila <amit.kapil...@gmail.com> writes:
>> Your patch would actually be needed if (and only if) autovacuum was >> changed back to its old behavior of never vacuuming toast tables >> independently, and if manual VACUUM pg_toast.*; was disabled. But in >> the presence of either of those two possibilities, it does nothing >> useful. Amit> Yeah, right, I have missed the point that they can be vacuumed Amit> separately, however, I think that decision is somewhat Amit> questionable. Some previous discussion links for reference, for the background to the thread containing the patch: https://www.postgresql.org/message-id/flat/87y7gpiqx3.fsf%40oxford.xeocode.com https://www.postgresql.org/message-id/flat/20080608230348.GD11028%40alvh.no-ip.org Amit> I think it would have been better if along with decoupling of Amit> vacuum for main heap and toast tables, we would have come up with Amit> a way to selectively remove the corresponding rows from the main Amit> heap, say by just vacuuming heap pages/rows which have toast Amit> pointers but maybe that is not viable or involves much more work Amit> without equivalent benefit. It should be fairly obvious why this is unworkable - most toast-using tables will have toast pointers on every page, but without making a whole new index of toast pointer OIDs (unacceptable overhead), it would be impossible to find the toast pointers pointing to a specific item without searching the whole rel (in which case we might just as well have vacuumed it). Amit> Also, we can think along the lines of another idea suggested by Amit> Andres [2] on the thread mentioned by you. That one is tricky for various reasons (locking, order of operations in vacuum_rel, having to mess with the API of vacuum(), etc.) -- Andrew (irc:RhodiumToad)
