Parallel reading from replicas #29279
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| /// We are the first who wants to process parts in partition | ||
| if (partition_it == partitions.end()) | ||
| { | ||
| auto part_and_projection = request.part_name + "#" + request.projection_name; |
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Why don't we store part name and projection separately?
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I want to underline their strict connectivity and also this concatenation simplifies the code a little bit (There are no additional checks that we want to read from the same projection). Maybe we can move them to std::pair or somewhat similar.
| result.intersect(intervals_to_do); | ||
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| /// Update intervals_to_do | ||
| intervals_to_do.intersect(HalfIntervals::initializeFromMarkRanges(std::move(request.mark_ranges)).negate()); |
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I think you should add some comments, from your paper :)
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Ok, just need to disable for |
…el-reading-from-replicas
KochetovNicolai
approved these changes
Dec 7, 2021
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@Mergifyio update |
✅ Branch has been successfully updated |
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Internal documentation ticket: DOCSUP-19955 |
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Changelog category (leave one):
Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):
Added an ability to read from all replicas within a shard during distributed query. To enable this, set
allow_experimental_parallel_reading_from_replicas=trueandmax_parallel_replicasto any number. This closes #26748Detailed description / Documentation draft:
We already have such mechanism, but it works only for tables with
SAMPLE BYkey. This feature will work for any kind of MergeTree tables. Ifmax_parallel_replicasis set to some value > 1, then the old algorithm is enabled (backward compatible change).