On Sat, Apr 27, 2019 at 5:13 PM Alexander Korotkov <a.korot...@postgrespro.ru> wrote: > Yes, increasing of Bloom filter size also helps. But my intention was > to make non-lossy check here.
Why is that your intention? Do you want to do this as a feature for Postgres 13, or do you want to treat this as a bug that we need to backpatch a fix for? Can we avoid the problem you saw with the Bloom filter approach by using the real size of the index (i.e. smgrnblocks()/RelationGetNumberOfBlocks()) to size the Bloom filter, and/or by rethinking the work_mem cap? Maybe we can have a WARNING that advertises that work_mem is probably too low? The state->downlinkfilter Bloom filter should be small in almost all cases, so I still don't fully understand your concern. With a 100GB index, we'll have ~13 million blocks. We only need a Bloom filter that is ~250MB to have less than a 1% chance of missing inconsistencies even with such a large index. I admit that its unfriendly that users are not warned about the shortage currently, but that is something we can probably find a simple (backpatchable) fix for. -- Peter Geoghegan
