Ticket #7504 (closed defect: duplicate)

Opened 3 years ago

Last modified 2 years ago

'Cannot operate on a closed cursor' exception causes db to appear as if upgrade is needed

Reported by: abeld Assigned to: athomas
Priority: normal Component: TagsPlugin
Severity: blocker Keywords: cursor
Cc: hasienda Trac Release: 0.12

Description (Last modified by rjollos)

I'm trying to configure an existing Trac instance to work from under virtualenv (trac 0.12 with SQLite, wsgi and apache). I ran into a situation where, after running trac-admin /path/to/env upgrade and wiki upgrade, trac, when being called by the webserver says that I have to run the upgrade (i.e. shows an error page to this effect). Running upgrade again on the command line says no upgrade necessary. That is, running trac from command-line and having it called from the webserver (via wsgi) gives two different results to the need to be upgraded? question.

I managed to track this down to the fact that TagModelProvider's environment_needs_upgrade returns True when being called from wsgi, and False when being called from the console. The problem appears to be that the cursor.execute('select count(*) from tags' ) line in there throws an exception, but not because the db is old, but because Cannot operate on a closed cursor.

Moving the cursor = db.cursor() line to below the 'if self._need_migration(db)', ie. to just above the try/except appears to solve this issue.

So, suggestions:

  1. the except: line in environment_needs_upgrade() shouldn't be so greedy, i.e. it shouldn't swallow all exceptions (if possible to filter out those caused by an old database)
  2. the 'cursor=db.cursor()' line should be moved to just above where it is first used.

Note that I assume the situation I ran into would be very difficult to reproduce, but the suggestions above won't have any drawbacks, and just help make the code cleaner.

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Change History

08/20/10 19:51:01 changed by rjollos

  • summary changed from 'Cannot operate on a closed cursor' eception causes db to appear as if upgrade is needed to 'Cannot operate on a closed cursor' exception causes db to appear as if upgrade is needed.

09/15/10 01:22:54 changed by doki_pen

I experience the same issue on a fresh install of trac running with tracd. The described fix (moving the cursor under the need_migration line) fixes it for me.

09/15/10 01:23:05 changed by doki_pen

  • severity changed from normal to blocker.

12/08/10 11:01:57 changed by rjollos

See also #6765, which has some useful information on this issue.

(follow-up: ↓ 7 ) 12/09/10 09:09:29 changed by rjollos

  • cc set to hasienda.

#5345 appears to be a duplicate. Or, at least much of what is discussed in the comments of that ticket appears to be a duplicate issue.

12/09/10 09:29:27 changed by rjollos

  • description changed.

In particular comment:5:ticket:5345 describes essentially the same fix, and several users report that the fix has successfully worked for them. The trunk has since been modified to move cursor = db.cursor() below if self._need_migration(db):, so it seems unlikely that the issue is that _need_migration is creating another cursor and forcing the close of the cursor in environment_needs_upgrade (see also [5655] and #4996). However, from what I've seen in this and other tickets, it seems to be important that the cursor is obtained within the try block.

I'm still trying to understand this issue, but as far as I can tell it would be at worst case harmless to move cursor = db.cursor() to within the try block.

(in reply to: ↑ 5 ) 07/06/11 00:34:09 changed by hasienda

  • keywords set to cursor.
  • status changed from new to closed.
  • resolution set to duplicate.

Replying to rjollos:

#5345 appears to be a duplicate. Or, at least much of what is discussed in the comments of that ticket appears to be a duplicate issue.

Confirmed, as you found yourself according to your findings in the following comment. Let's make this trivial fix, before we get even more reasonable complaints, NOW. Following up over there...

Add/Change #7504 ('Cannot operate on a closed cursor' exception causes db to appear as if upgrade is needed)




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