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Lazy loading of primary keys in memory #60093

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merged 13 commits into from
Feb 19, 2024
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@alexey-milovidov alexey-milovidov commented Feb 17, 2024

Changelog category (leave one):

  • Performance Improvement

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

The tables' primary keys will be loaded in memory lazily on first access. This is controlled by the new MergeTree setting primary_key_lazy_load, which is on by default. This provides several advantages: - it will not be loaded for tables that are not used; - if there is not enough memory, an exception will be thrown on first use instead of at server startup. This provides several disadvantages: - the latency of loading the primary key will be paid on the first query rather than before accepting connections; this theoretically may introduce a thundering-herd problem. This closes #11188.

@robot-ch-test-poll robot-ch-test-poll added the pr-performance Pull request with some performance improvements label Feb 17, 2024
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robot-ch-test-poll commented Feb 17, 2024

This is an automated comment for commit 8d6e6d6 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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@CurtizJ CurtizJ self-assigned this Feb 17, 2024
@alexey-milovidov alexey-milovidov merged commit 6c2c171 into master Feb 19, 2024
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@alexey-milovidov alexey-milovidov deleted the lazy-primary-key-loading branch February 19, 2024 00:36
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pr-backports-created-cloud pr-must-backport-cloud pr-performance Pull request with some performance improvements pr-synced-to-cloud The PR is synced to the cloud repo
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Protection from too large size of index in memory.
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