#35399: Reduce the "Case-When" sequence for a bulk_update when the values for a
certain field are the same.
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Reporter: Willem Van Onsem | Owner: nobody
Type: | Status: closed
Cleanup/optimization |
Component: Database layer | Version: 5.0
(models, ORM) |
Severity: Normal | Resolution: duplicate
Keywords: db, bulk_update, | Triage Stage:
case, when | Unreviewed
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 Simon Charette):
> it will raise a type error: we catch that, and then fallback on the
original way of doing it, without much delay.
Creating and catching exceptions is not cheap either so I'm not sure we
can qualify it as ''without much delay''. I don't see any benchmark
backing it is what I mean.
> the idea is that this often will still pay off, since the cascade of
Case - When essentially forces the database into linear search
I see what you mean with the database level linear scan but my concerns is
that the extra amount time we spend ''massaging'' the data on the Python
side pre-emptively in hope of preventing the database level slowdown from
happening is going to cause more harm than good.
You benchmarked against are the ''happy path'' where a there's a single
field to update, the values are all literals, the values are all hashable.
I think that a proper solution should ensure that the ''Python layer tax''
of organizing the data doesn't outweigh the expected database level
benefits.
Having separate benchmarks for query / SQL generation in both variants of
`bulk_update` vs database level execution of the SQL on supported backends
would help in taking more advised decision here. All of that can take
place on the forum though.
--
Ticket URL: <https://code.djangoproject.com/ticket/35399#comment:7>
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