#3460: postgresql_psycopg2 backend uses wrong isolation level
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Reporter: Jack Moffitt <metaj...@gmail.com> | Owner:
Richard Davies <richard.dav...@elastichosts.com>
Status: new | Milestone:
Component: Database layer (models, ORM) | Version: SVN
Resolution: | Keywords:
Stage: Design decision needed | Has_patch: 1
Needs_docs: 0 | Needs_tests: 0
Needs_better_patch: 1 |
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Comment (by iamseb):
Following up from nicferrier's patch, there's a corresponding issue when
using transaction pooling which must be resolved.
INSERT statements followed by SELECT CURRVAL for creating new objects may
split the queries over two transactions, and therefore two sessions. The
second session will not have the sequence value available. In this case, a
far safer route is to use the RETURNING clause in INSERT statements to
return the new value for the pk.
The attached insertwithreturning.patch adds a new feature to
BaseDatabaseFeatures, sets it to true for the psycopg2 backend, and
conditionally creates an appropriate RETURNING clause for INSERT
statements.
This feature is supported for PostgreSQL 8+ with psycopg2 (tested), and
Oracle (untested, currently not enabled).
With these two patches, correct transaction isolation support for postgres
is fully implemented, and scaling issues with lock concurrency and hanging
transactions are mitigated. (We've seen >10k locks reduced to <100.)
--
Ticket URL: <http://code.djangoproject.com/ticket/3460#comment:25>
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