Make scan filter push-down idempotent #20003
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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`.
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Will fix CI soon. |
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.
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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.