#36248: Bulk deletion of model referred to by a SET_NULL key can exceed
parameter
limit
-------------------------------------+-------------------------------------
Reporter: bobince | Owner: bobince
Type: Bug | Status: assigned
Component: Database layer | Version: 5.1
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by bobince):
> I guess I could scrape the SQL string for number of integers but this
feels pretty fragile.
Have tried something similar to this (counting commas in ‘IN’ clauses) and
actually maybe it's not thaaat bad. I've written worse.
Now I have a test that's only counting parameters not queries, I tried
using the existing test model ‘R’ instead of making a new one. This turned
up an delightful wrinkle in that the fast-delete path can also ‘OR’
together multiple querysets, this time when there are multiple references
on one model to rows being deleted. For example if Article.author and
Article.editor are ForeignKeys to Person with on_delete=CASCADE, and 500
Person rows are deleted, deletion will put together a query like `DELETE
FROM article WHERE author IN (...500 params...) OR editor IN (...another
500 params...)` and if you have a DBMS with a param limit of 999 you're
now sad.
So, er, back to simpler relations for now. I don't think there's a
straightforward fix to this — it would take a more wide-ranging rethink of
how param limits impact batch sizes and I don't really have a good idea
what that would look like. Ugh, I wish param limits would go away
--
Ticket URL: <https://code.djangoproject.com/ticket/36248#comment:6>
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