bad rewriting of query involving targetList indirection: "UPDATE SET (col2, col1, col3)" #7674
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Similar to #4092 which focus on reference table. |
c2main
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Nov 19, 2024
ruleutils in Citus is based on PostgreSQL source code, but in PostgreSQL ruleutils is not used at the planner stage. For instance, it is assumed after parser that targetList are ordered as they were read, but it's not true after rewriter, the resulting rewrite tree is then provided to planner (and citus), but the ordering of the list is not granted anymore. It's similar to others previous issues reported and still open, as well as to other bugfixes/improvment over time, the most noticable being the ProcessIndirection() which is for domain and similar. However, the implications of this bug are huge for users of `UPDATE SET (...)`: 1. if you used to order by columns order, you're maybe safe: `SET (col1, col2, col3, ...)` 2. if you used not to order by column order: `SET (col2, col1, col3, ...)` then you probably found a problem, or you have one. Note about 1. that despite appearance and your QA, you are at risk: if physical columns ordering is changed (for example after DROPping/ADDing some), the same query which use to apparently works well will silently update other columns... As it is this code is not optimized for performance, not sure it'll be needed.
c2main
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Nov 22, 2024
This reverts commit 73f4f67.
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A customer reported a bug from development team affecting queries with
UPDATE SET (col2, col1, col3) = (.....)The columns are reordered following their physical ordering in pg_attribute, leading to for example
UPDATE SET (col1, col2, col3) = (.....)with the right part, after=unchanged, as a results wrong columns are updated...I have a complete test case, and a PR which I'm going to link in a moment. I think the issue may affect silently many applications, even more because the behavior can change over time based on the DDL applied on the updated tables.
There are several issue, I'm going to collect what I fond and link here so maybe we can close several at once...
Please see https://github.com/citusdata/citus/actions/runs/10527721147#summary-29171656391 for some examples of the problem.
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