#9964: Transaction middleware closes the transaction only when it's marked as
dirty
---------------------------------------------------+------------------------
Reporter: ishirav | Owner:
mtredinnick
Status: assigned | Milestone: 1.3
Component: Database layer (models, ORM) | Version: 1.0-beta-1
Resolution: | Keywords:
transactions
Stage: Accepted | Has_patch: 1
Needs_docs: 1 | Needs_tests: 0
Needs_better_patch: 0 |
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Comment (by seanc):
I would argue that this is more than a simple cosmetic bug, and that
fixing this has a huge set of benefits. A few additional notes:
1) PostgreSQL can't get rid of versions of tuples that are held inside of
a read transaction (e.g. a VACUUM can't reap rows that have been read in a
transaction until the transaction is closed)
2) Users of pgbouncer with their pool_mode set to 'transaction' aren't
free'ing up the backend, which dramatically cuts the effectiveness of
pgbouncer.
{{{
; When server connection is released back to pool:
; session - after client disconnects
; transaction - after transaction finishes
; statement - after statement finishes
pool_mode = transaction
}}}
3) Neither COMMIT or ROLLBACK will perform any better than the other. See
the following thread for some small details.
http://www.mail-archive.com/pgsql-gene...@postgresql.org/msg60957.html
One important catch to keep in mind is that SELECT can call functions that
modify tables. COMMITs will provide better "do what I expect" behavior,
but I would argue that users of functions that modify data should be
explicit in their COMMITs.
Based on what I've read in the thread above, adding three new versions of
the TransactionMiddleware appears to provide the easiest path forward.
"TransactionMiddlewareRollback," "TransactionMiddlewareCommit," and
"TransactionMiddlewareOpen". Copy TransactionMiddleware to
TransactionMiddlewareOpen and have TransactionMiddleware issue a warning
on startup that the developer should switch to Rollback or Commit (or Open
to preserve the current buggy functionality). In a future version, change
TransactionMiddleware to use TransactionMiddlewareRollback as the default
or just remove it all together. I'd rather see an explicit behavior
configured as a Middleware class vs. an entry in settings.py.
--
Ticket URL: <http://code.djangoproject.com/ticket/9964#comment:22>
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