Filter(s) aggregation should create weights only once. #15998
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LGTM |
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Any opinions about whether to backport to 2.2? |
We have a performance bug that if a filter aggregation is below a terms aggregation that has a cardinality of 1000, we will call Query.createWeight 1000 times as well. However, Query.createWeight can be a costly operation. For instance in the case of a TermQuery it will seek the term in every segment. Instead, we should create the Weight once, and then get as many iterators as we need from this Weight. I found this problem while trying to diagnose a performance regression while upgrading from 1.7 to 2.1[1]. While the problem was not introduced in 2.x, the fact that 1.7 cached very aggressively had hidden this problem, since you don't need to seek the term anymore on a cached TermFilter. Doing things once for every aggregator is not easy with the current API but I discussed this with Colin and Aggregator factories will need to get an init method for different reasons, where we will be able to put these steps that need to be performed only once, no matter haw many aggregators need to be created. [1] https://discuss.elastic.co/t/aggregations-in-2-1-0-much-slower-than-1-6-0/38056/26
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…_once Filter(s) aggregation should create weights only once.
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We have a performance bug that if a filter aggregation is below a terms
aggregation that has a cardinality of 1000, we will call Query.createWeight
1000 times as well. However, Query.createWeight can be a costly operation.
For instance in the case of a TermQuery it will seek the term in every
segment. Instead, we should create the Weight once, and then get as many
iterators as we need from this Weight.
I found this problem while trying to diagnose a performance regression while
upgrading from 1.7 to 2.1[1]. While the problem was not introduced in 2.x, the
fact that 1.7 cached very aggressively had hidden this problem, since you don't
need to seek the term anymore on a cached TermFilter.
Doing things once for every aggregator is not easy with the current API but
I discussed this with Colin and Aggregator factories will need to get an init
method for different reasons, where we will be able to put these steps that
need to be performed only once, no matter haw many aggregators need to be
created.
[1] https://discuss.elastic.co/t/aggregations-in-2-1-0-much-slower-than-1-6-0/38056/26