Robert Haas wrote: > If I understand correctly, we currently deem an update to be non-HOT > whenever any indexed column is updated. This is because tuple > versions created by HOT updates can later be removed by HOT pruning, > which means that they must not be referenced by index entries. > Otherwise, after HOT pruning removed the tuple, the index entries > would at best be pointing at nothing and at worse be pointing at some > completely unrelated tuple. > > But what about index types that do not store TIDs - i.e. BRIN?
Oh, I had a note to get back to the topic of HOT updates and it fell through the cracks :-( You're right, this needs to be addressed. > If the > indexed column is updated, we can't actually create a Heap Only Tuple > (HOT), because then the index might be wrong. But we could create a > Heap Mostly Tuple. We'd construct the update chain in the heap > page just as we would for HOT, and set all the same flags. But then > we'd also insert new index entries for any TID-free indexes, currently > just BRIN. For BRIN, that would have the effect of updating the > summary data for that page in such a way that it would encompass both > the old and new values. Sounds reasonable. -- Álvaro Herrera http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers