Re: WIP: bloom filter in Hash Joins with batches
| От | Simon Riggs |
|---|---|
| Тема | Re: WIP: bloom filter in Hash Joins with batches |
| Дата | |
| Msg-id | CANP8+jKT=Vzv92mSv1Lh2tmeHyhmNBfa5xG6r1msgBT5QDf1Aw@mail.gmail.com обсуждение исходный текст |
| Ответ на | WIP: bloom filter in Hash Joins with batches (Tomas Vondra <tomas.vondra@2ndquadrant.com>) |
| Ответы |
Re: WIP: bloom filter in Hash Joins with batches
|
| Список | pgsql-hackers |
On 15 December 2015 at 22:30, Tomas Vondra <tomas.vondra@2ndquadrant.com> wrote:
--
3) Currently the bloom filter is used whenever we do batching, but it
should really be driven by selectivity too - it'd be good to (a)
estimate the fraction of 'fact' tuples having a match in the hash
table, and not to do bloom if it's over ~60% or so. Also, maybe
the could should count the matches at runtime, and disable the
bloom filter if we reach some threshold.
Cool results.
It seems a good idea to build the bloom filter always, then discard it if it would be ineffective.
My understanding is that the bloom filter would be ineffective in any of these cases
* Hash table is too small
* Bloom filter too large
* Bloom selectivity > 50% - perhaps that can be applied dynamically, so stop using it if it becomes ineffective
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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