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Lower memory usage in vertical merges #59340

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merged 1 commit into from Jan 30, 2024
Merged

Lower memory usage in vertical merges #59340

merged 1 commit into from Jan 30, 2024

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CurtizJ
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@CurtizJ CurtizJ commented Jan 29, 2024

Changelog category (leave one):

  • Performance Improvement

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Lower memory usage in vertical merges

Fixes #57773.

@robot-ch-test-poll2 robot-ch-test-poll2 added the pr-performance Pull request with some performance improvements label Jan 29, 2024
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robot-ch-test-poll2 commented Jan 29, 2024 •
edited by robot-clickhouse-ci-1

This is an automated comment for commit d3cdc88 with description of existing statuses. It's updated for the latest CI running

❌ Click here to open a full report in a separate page

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Check nameDescriptionStatus
AST fuzzerRuns randomly generated queries to catch program errors. The build type is optionally given in parenthesis. If it fails, ask a maintainer for help✅ success
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CurtizJ
CurtizJ commented Jan 29, 2024
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tests/queries/0_stateless/02981_vertical_merges_memory_usage.sql

SELECT
merge_algorithm,
peak_memory_usage < 500 * 1024 * 1024
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peak_memory_usage before: 4.57 GiB, after: 89.95 MiB.

@nickitat nickitat self-assigned this Jan 29, 2024
nickitat
nickitat approved these changes Jan 29, 2024
View reviewed changes
src/Processors/Transforms/ColumnGathererTransform.h
while (row_source_pos < row_sources_end && cur_size < cur_block_preferred_size)
while (row_source_pos < row_sources_end
&& column_res.size() < block_preferred_size_rows
&& column_res.allocatedBytes() < block_preferred_size_bytes)
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really minor. maybe it makes sense to use byteSize() because I'd expect block_size_bytes to refer to the actual data size.

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I checked that allocatedBytes is used inMergedData and did the same. But we can change it in both places.

@alexey-milovidov alexey-milovidov merged commit 50532c4 into ClickHouse:master Jan 30, 2024
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@CurtizJ CurtizJ mentioned this pull request Feb 9, 2024
Merged
azat added a commit to azat/ClickHouse that referenced this pull request Feb 13, 2024
@azat
tests: fix 02981_vertical_merges_memory_usage flakiness
f3f7f5c 
Note, that I've checked this change by reverting ClickHouse#59340, i.e.

    diff --git a/src/Processors/Transforms/ColumnGathererTransform.h b/src/Processors/Transforms/ColumnGathererTransform.h
    index 4e56cffa46a..dd3c555f361 100644
    --- a/src/Processors/Transforms/ColumnGathererTransform.h
    +++ b/src/Processors/Transforms/ColumnGathererTransform.h
    @@ -195,7 +195,7 @@ void ColumnGathererStream::gather(Column & column_res)
             }

             source.pos += len;
    -    } while (column_res.size() < block_preferred_size_rows && column_res.byteSize() < block_preferred_size_bytes);
    +    } while (true);
     }

     }

And it fails:

    02981_vertical_merges_memory_usage:                                     [ FAIL ] - result differs with reference:
    --- /src/ch/clickhouse/tests/queries/0_stateless/02981_vertical_merges_memory_usage.reference   2024-02-13 10:37:54.771393874 +0100
    +++ /src/ch/clickhouse/tests/queries/0_stateless/02981_vertical_merges_memory_usage.stdout      2024-02-13 10:41:06.781109565 +0100
    @@ -1 +1 @@
    -Vertical       OK
    +Vertical       FAIL: memory usage: 626.59 MiB

Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>
@azat azat mentioned this pull request Feb 13, 2024
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azat commented Feb 21, 2024

FWIW this patch changes serialization for LowCardinality, so you can get DataAfterMergeDiffersFromReplica (We will download merged part from replica to force byte-identical result.) error during upgrading replicas

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@nickitat nickitat nickitat approved these changes

@alexey-milovidov alexey-milovidov alexey-milovidov approved these changes

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Vertical merge could consume a lot of memory
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@CurtizJ @robot-ch-test-poll2 @azat @nickitat @alexey-milovidov @robot-clickhouse-ci-1