Hi,
On 2019-02-28 12:36:50 -0500, Robert Haas wrote:
> Well, Andres will probably complain about that. He thinks, IIUC, that
> the buffer tags are too wide already and that it's significantly
> hurting performance on very very common operations - like buffer
> lookups.
Correct. Turns out especially comparing the keys after the hash match is
pretty expensive. It also is a significant factor influencing the size
of the hashtable, which influences how much of it can be in cache.
My plan is still to move to a two tiered system, where we have one
unordered datastructure to map from (db, tablespace, oid) to a secondary
ordered datastructure that then maps from (block number) to an actual
offset. With the first being cached somewhere in RelationData, therefore
not being performance critical. But while I hope to work for that in 13,
I don't think making other large projects depend on it would be smart.
Greetings,
Andres Freund