Make scan filter push-down idempotent #20003
Open
+214
−32
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
236ef40 to
6697447
Compare
Contributor
Author
|
Will fix CI soon. |
6697447 to
b3c756b
Compare
Part of apache#19929 Let "t" be a table provider that supports exactly any single filter but not a conjunction. Consider the following optimizer pipeline: 1. Try to push `a = 1, b = 1`. `supports_filters_pushdown` returns [Exact, Inexact] OK: the optimizer records that a = 1 is pushed and creates a filter node for b = 1. ... Another optimization iteration. 2. Try to push `b = 1`. `supports_filters_pushdown` returns [Exact]. Of course, the table provider can't remember all previously pushed filters, so it has no choice but to answer `Exact`. Now, the optimizer thinks the conjunction a = 1 AND b = 1 is supported exactly, but it is not. To prevent this problem, this patch passes filters that were already pushed into the scan earlier to `supports_filters_pushdown`.
Consider the following optimizer-run scenario: 1. `supports_filters_pushdown` returns `Exact` on some filter, e.g. "a = 1", where the column "a" is not required by the query projection. 2. "a" is removed from the table provider projection by "optimize projection" rule. 3. `supports_filters_pushdown` changes a decision and returns `Inexact` on this filter the next time. e.g., input filters are changed and it prefers to use a new one. 4. "a" is not returned to the table provider projection which leads to filter that references a column which is not a part of the input schema. This patch fixes issue introducing the following logic within a filter push-down rule: 1. Collect columns that are not used in the current table provider scan projection, but required for filter expressions. Call it `additional_projection`. 2. If `additional_projection` is empty -- leave logic as is prior the patch. 3. Otherwise extend a table provider projection and wrap a plan with an additional projection node to preserve schema used prior to the rule.
b3c756b to
52cb896
Compare
xudong963
reviewed
Jan 27, 2026
Comment on lines
+1222
to
+1223
| // Extend a projection. | ||
| projection.extend(additional_projection); |
Member
There was a problem hiding this comment.
There should be a tradeoff between fetching an extra column from storage vs the selectivity of the related filter
Contributor
Author
There was a problem hiding this comment.
It seems for me that the change only touches correctness of the rule (not performance), here we must extend projection (because filter is explicitly not supported by the provider).
Comment on lines
+1206
to
+1207
|
|
||
| if additional_projection.is_empty() { |
Member
There was a problem hiding this comment.
The branch of scan is expanding, any thoughts to split the branch
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 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.
Which issue does this PR close?
Rationale for this change
Non-idempotent rule logic leads to the artifacts described in the issue above if the rule is applied several times.
What changes are included in this PR?
supports_filter_pushdown(...)call.Are these changes tested?
There are unit tests.