release-25.3: opt: estimate worst-case selectivity of placeholder equalities #156791
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
|
Thanks for opening a backport. Before merging, please confirm that the change does not break backwards compatibility and otherwise complies with the backport policy. Include a brief release justification in the PR description explaining why the backport is appropriate. All backports must be reviewed by the TL for the owning area. While the stricter LTS policy does not yet apply, please exercise judgment and consider gating non-critical changes behind a disabled-by-default feature flag when appropriate. |
blathers-crl
bot
added
backport
Member
|
This change is |
mgartner
changed the title
michae2
approved these changes
Nov 3, 2025
Collaborator
michae2
left a comment
michae2
left a comment
There was a problem hiding this comment.
@michae2 reviewed 14 of 14 files at r1, 10 of 10 files at r2, all commit messages.
Reviewable status:complete! 1 of 0 LGTMs obtained (waiting on @mgartner)
Previously, we calculated the selectivity of placeholder equality filters, e.g., `x = $1`, using the distinct count of a column and total row count. This represented an average-case selectivity. Now, we instead estimate the worst-case selectivity using the maximum frequency of the histogram of the constrained column. This helps avoid choosing a generic query plan under `plan_cache_mode=auto` that performs poorly for heavy-hitter placeholder values. Fixes cockroachdb#151373 Release note (performance improvement): The cost of generic query plans is now calculated based on worst-case selectivities for placeholder equalities (e.g., x = $1). This reduces the chance of suboptimal generic query plans being chosen when `plan_cache_mode=auto`.
The `optimizer_use_max_frequency_selectivity` session setting has been added. It is enabled by default. Disabling it reverts the selectivity improvements added in cockroachdb#151409. Release note: None
mgartner
force-pushed
the
backport25.3-151409-156654
branch
from
7509c85 to
6bfc131
Compare
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
3 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Backport:
Please see individual PRs for details.
/cc @cockroachdb/release
Release justification: Low-risk planning improvement for generic query plans.