#9136: Oracle backend: slicing is using row_number() instead of rownum
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Reporter: Guillaume Taglang <[EMAIL PROTECTED]> | Owner: nobody
Status: new |
Milestone:
Component: Database layer (models, ORM) |
Version: 1.0
Keywords: |
Stage: Unreviewed
Has_patch: 0 |
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Doing Entity.objects.all()[:10] is generating a query like:
{{{
SELECT *
FROM (SELECT (ROW_NUMBER() OVER (ORDER BY "ENTITY"."ID")) AS "_RN",
"ENTITY"."ID", "ENTITY"."NAME"
FROM "ENTITY")
WHERE "_RN" > 0
AND "_RN" <= 10
}}}
This is suboptimal as a full table scan is forced (at least in 10g).
Using ''rownum'' instead of ''row_number()'' is faster (it can use
indexes), and doesn't require an ''order by'' clause when not required.
The query would look like:
{{{
SELECT "ENTITY"."ID", "ENTITY"."NAME"
FROM "ENTITY"
WHERE ROWNUM > 0 AND ROWNUM <= 10
ORDER BY "ENTITY"."ID"
}}}
It won't make a noticeable difference with tables with a couple of rows;
but when you are reaching the million rows, you go from minutes to
milliseconds.
--
Ticket URL: <http://code.djangoproject.com/ticket/9136>
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