Robert Haas <robertmhaas@gmail.com> writes:
> On Tue, Aug 29, 2017 at 10:22 PM, Thomas Munro
> <thomas.munro@enterprisedb.com> wrote:
>> (2) We could push a Bloom filter down to scans
>> (many other databases do this, and at least one person has tried this
>> with PostgreSQL and found it to pay off[1]).
> I think the hard part is going to be figuring out a query planner
> framework for this, because pushing down the Bloom filter down to the
> scan changes the cost and the row-count of the scan.
Uh, why does the planner need to be involved at all? This seems like
strictly an execution-time optimization. Even if you wanted to try
to account for it in costing, I think the reliability of the estimate
would be nil, never mind any questions about whether the planner's
structure makes it easy to apply such an adjustment.
Personally though I would not bother with (2); I think (1) would
capture most of the win for a very small fraction of the complication.
Just for starters, I do not think (2) works for batched hashes.
regards, tom lane
--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers