#34811: Queryset filter Q order changed
-------------------------------------+-------------------------------------
Reporter: | Owner: nobody
cosmoscalibur |
Type: Bug | Status: new
Component: Database | Version: 4.2
layer (models, ORM) |
Severity: Normal | Keywords: filter, Q
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-------------------------------------+-------------------------------------
Using filters in order explicitly expressed by user is important because
take advantage of indexes.
When apply this query
{{{
TaxInput.objects.all(
force_visibility=True
).filter(
Q(filling_id=pk, updated_at__gt=last_engine.created_at)
| Q(filling_id=pk, deleted__gt=last_engine.created_at),
)
}}}
the MySQL generated query is
{{{
SELECT
*
FROM
`taxobjects_taxinput`
WHERE
( `taxobjects_taxinput` . `filling_id` = ?
AND `taxobjects_taxinput` . `updated_at` > ? )
OR ( `taxobjects_taxinput` . `deleted` > ?
AND `taxobjects_taxinput` . `filling_id` = ? )
LIMIT
?
}}}
But should be
{{{
SELECT
*
FROM
`taxobjects_taxinput`
WHERE
( `taxobjects_taxinput` . `filling_id` = ?
AND `taxobjects_taxinput` . `updated_at` > ? )
OR ( `taxobjects_taxinput` . `filling_id` > ?
AND `taxobjects_taxinput` . `deleted` = ? )
LIMIT
?
}}}
This change of order create a 10x factor in query time, because this table
has index filing_id, and also index (filing_id, deleted).
Using Django 4.2.1 and SafeDelete 1.3.1 (because this is used
force_visibility=True in all manager).
--
Ticket URL: <https://code.djangoproject.com/ticket/34811>
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