Hello it looks interesting - please, try to send some performance results,
Regards Pavel 2013/6/26 Atri Sharma <atri.j...@gmail.com>: > Hi All, > > I have been researching bloom filters and discussed it on IRC with > RhodiumToad and David Fetter, and they pointed me to the various > places that could potentially have bloom filters, apart from the > places that already have them currently. > > I have been reading the current implementation of hash joins, and in > ExecScanHashBucket, which I understand is the actual lookup function, > we could potentially look at a bloom filter per bucket. Instead of > actually looking up each hash value for the outer relation, we could > just check the corresponding bloom filter for that bucket, and if we > get a positive, then lookup the actual values i.e. continue with our > current behaviour (since we could be looking at a false positive). > > This doesn't involve a lot of new logic. We need to add a bloom filter > in HashJoinState and set it when the hash table is being made. Also, > one thing we need to look at is the set of hash functions being used > for the bloom filters. This can be a point of further discussion. > > The major potential benefit we could gain is that bloom filters never > give false negatives. So, we could save a lot of lookup where the > corresponding bloom filter gives a negative. > > This approach can also be particularly useful for hash anti joins, > where we look for negatives. Since bloom filters can easily be stored > and processed, by straight bit operations, we could be looking at a > lot of saving here. > > I am not sure if we already do something like this. Please direct me > to the relevant parts in the code if we already do. > > Regards, > > Atri > > -- > Regards, > > Atri > l'apprenant > > > -- > Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-hackers -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
