Evaluate what to do with function side-effects
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Assessment
- Difficulty
- 5/5
- Estimated time
- Over a week
- Newbie friendliness
- 25/100
Research direction
The issue concerns mapping functions in the query tree and the risks of removing or duplicating calls during optimization. No files, tests, or entry points are named, so begin by locating query translation and optimization handling for mapping functions. Done requires an agreed policy for side effects and the corresponding behavior to be specified and validated.
Written by the indexing model from the issue text.
Description
We allow mapping functions (both by providers and by users), and treat these like any other expression node in the query tree. However, functions are unique among SQL nodes in that they can have side-effects, so either removing them (because of an optimization) or duplicating them (e.g. to add a null check) could lead to data corruption.
One possibility here is to assume functions are pure (no side effects), but allow users to tell us that they are non-pure. In that case, we'd avoid optimizing the call away, and throw in cases where duplicating it would be necessary to translate correctly.
Note: regardless of functions and side effects, it seems to be we should be very wary of duplicating subtrees of unknown depth/contents in the query (because of the perf impact).
- Dominant language
- C#
- Stars
- 14.8k
- Forks
- 3.4k
- Avg merge
- 2d 5h
- Merged PRs (30d)
- 134
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
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