#12579: QuerySet.get_or_create()'s behavior depends on database's uniqueness
restrictions
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Reporter: timmolendijk | Owner: nobody
Type: Bug | Status: new
Component: Documentation | Version: 1.0
Severity: Normal | Resolution:
Keywords: get_or_create | Triage Stage: Accepted
concurrency race unique | Needs documentation: 0
documentation | Patch needs improvement: 0
Has patch: 0 | UI/UX: 0
Needs tests: 0 |
Easy pickings: 1 |
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Comment (by jdunck):
We (Votizen) were seeing the REPEATABLE READ visibility problem (described
in the StackOverflow link above) on mysql+innodb+REPEATABLE READ. To me,
the suggestion on StackOverflow- of committing whatever transaction is
pending - is bogus. Transactions need to be composable, and committing so
you can read means you can't combine this function with any other function
that requires an ongoing transaction.
We switched (about 6 months ago) to READ COMMITTED. This reduces
throughput in mysql, but is a good tradeoff to me.
I think that since MySQL's innodb default transaction isolation is
incompatible with Django's get_or_create approach, it would be good to
either note in the docs for get_or_create, or advise setting READ
COMMITTED for all users of mysql.
--
Ticket URL: <https://code.djangoproject.com/ticket/12579#comment:7>
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