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https://issues.apache.org/jira/browse/IMPALA-10112?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17186048#comment-17186048
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Riza Suminto commented on IMPALA-10112:
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Hi [~tarmstrong], my understanding is that that FPP check might be still useful
to prevent sending filter that is too big and not efficient anyway.
Like, if the filter size is high enough and the FPP is also high, then
definitely just send ALWAYS_TRUE_FILTER.
If FPP is high but filter size is still acceptable for transmission, then maybe
it is more beneficial to send it.
I'm not aware of what is the acceptable threshold of such filter size.
> Consider skipping FpRateTooHigh() check for bloom filters
> ---------------------------------------------------------
>
> Key: IMPALA-10112
> URL: https://issues.apache.org/jira/browse/IMPALA-10112
> Project: IMPALA
> Issue Type: Improvement
> Components: Backend
> Reporter: Tim Armstrong
> Assignee: Tim Armstrong
> Priority: Major
> Labels: performance
>
> This check disables bloom filters on the sender side.
> It is inaccurate in cases where there are duplicate values of the filter key
> on the build side. E.g. many-to-many join or a join with multiple keys. This
> could be fixed with some effort, but is probably not worth it, because:
> * Partition filters are probably still worth evaluating even if there are
> false positives, because it's cheap and eliminating a partition is still
> beneficial.
> * Runtime filters are dynamically disabled on the scan side if they are
> ineffective. I think we still also "evaluate" the always true filter, which
> is cheaper than doing the hashing and bloom evaluation, but still not
> entirely free.
> * The disabling is fairly unlikely to kick in for partitioned joins because
> it's only applied to a small subset of the filter, before the Or() operation.
> So it's potentially harmful and only likely beneficial for broadcast join
> filters, in which case it saves a small amount of scan CPU and, for global
> filters, coordinator RPCs and broadcasting. It's unclear that the complexity
> is worth it for this relatively small and uncertain benefit.
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