What is a Bloom filter ?

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When you start seeing strange "BF" tags in your execution plan, you are probably getting the benefit of a Bloom filter. But was is a Bloom filter, and why is it relevant when it comes to queries in the Oracle database?
Bloom filter theory en.wikipedia.o...
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11 сен 2024

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Комментарии : 6

@Youhavebeenprogrammed 2 года назад

Is there any parameter I need to enable to make BF work?, thanks

@DatabaseDude 2 года назад

nope. they are part of the database

@berndeckenfels 3 года назад

Are there any persistent or shared bloom filters bittest in Oracle or are they all recalculated in the PGA?

@DatabaseDude 3 года назад

To my knowledge, they are a PGA structure. They aren't large (just a hash array)

@haroon9445 2 года назад

Hi Connor, Thanks for explaining this topic nicely. I have below doubts regarding this topic 1. Bloom filter pruning is also dynamic partition pruning? (My doubt is that Oracle documentation does not mention bloom filter pruning as Dynamic partition pruning method in this document docs.oracle.com/en/database/oracle/oracle-database/21/vldbg/partition-pruning.html#GUID-DF8D6743-8786-4D7A-ACDF-0091F8E2FE3B) 2. Is it possible to trace the partitions that the query scanned using bloom filter? 3. Please can you also explain the concept Key vector create buffered and use (in pstart and pstop) ? (It will be really helpful for us ) Many Thanks, Sahal Haroon

@DatabaseDude 2 года назад

- I'd say that a doc bug, because its very rare you'll ever see "KEY(SQ)" in a plan anymore - we almost always go for bloom filters in this case. - event 10128 might help here - see docs.oracle.com/en/database/oracle/oracle-database/19/inmem/optimizing-in-memory-aggregation.html#GUID-A9E6044E-DC81-44C7-8D0C-E77502722388 for how it pertains to in-memory, but the concepts are the same. We're taking advantage of some hardware capabilities