Cherry pick #80777 to 25.3: Fix excessive number of files (leads to excessive memory usage) for external ORDER BY#80952
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robot-clickhouse-ci-2 merged 8 commits intobackport/25.3/80777from May 28, 2025
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…xternal ORDER BY In #72598 the behavior of `max_bytes_before_external_sort` has been changed, it has been switched to rely on the total memory usage of the query instead of the size of a sorting data. But, the problem with this approach is that you can have a lot of memory used outside of sorting (FINAL, aggregation), and spilling sorting blocks to disk will not help reduce memory usage obviously, but it will make things even worse, because it will create lots of small files, that will require a lot of memory to merge them. So this patch reverts the behavior of `max_bytes_before_external_sort` back, now it will rely on the sorting block size.
Set max_bytes_before_external_sort=min_external_sort_block_bytes=100Mi
The problem is that now both conditions should be met: - max_bytes_ratio_before_external_sort - max_bytes_before_external_sort So it is not possible to use max_bytes_ratio_before_external_sort=0.9, this will lead to MEMORY_LIMIT_EXCEEDED errors
Fix excessive number of files (leads to excessive memory usage) for external ORDER BY
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Original pull-request #80777
This pull-request is a first step of an automated backporting.
It contains changes similar to calling
git cherry-picklocally.If you intend to continue backporting the changes, then resolve all conflicts if any.
Otherwise, if you do not want to backport them, then just close this pull-request.
The check results does not matter at this step - you can safely ignore them.
Note
This pull-request will be merged automatically. Please, do not merge it manually (but if you accidentally did, nothing bad will happen).
Troubleshooting
If the PR was manually reopened after being closed
If this PR is stuck (i.e. not automatically merged after one day), check #80777 for
pr-backports-createdlabel and delete it.Manually merging will do nothing. The
pr-backports-createdlabel prevents the original PR #80777 from being processed.If the conflicts were resolved in a wrong way
If this cherry-pick PR is completely screwed by a wrong conflicts resolution, and you want to recreate it:
pr-cherrypicklabel from the PRYou also need to check the original PR #80777 for
pr-backports-created, and delete if it's presented thereThe PR source
The PR is created in the CI job