#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
Resolution:
| Keywords:
Stage: Unreviewed
| Has_patch: 1
Needs_docs: 0
| Needs_tests: 0
Needs_better_patch: 0
|
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Comment (by gtaglang):
The change to the query in [9221] fixes my main gripes about slicing with
oracle.
My own test on a set of table with some real data do not show any
significant difference between rownum and row_number() for the first few
rows, however as the number of rows increase row_number() gets
significantly slower.
If you look at the result of an explain plan you will easily understand
why: row_number() is an analytic function and the database needs to apply
the function first; rownum on the oder hand is built in the query and
costs nothing. Depending on data and indexes the cost difference between
rownum and row_number(), as calculated by the optimizer, can reach several
order of magnitude. (At least for my release of Oracle: 10.2 Enterprise.)
(As a side note: 870ms per query for the table you mentioned is really
bad. Are you sure you did execute the tests with warm and/or cold cache
for both rownum and row_number() ?)
(Second side note: looks like the spam filter is a tad overzealous.)
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Ticket URL: <http://code.djangoproject.com/ticket/9136#comment:4>
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