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#81 ✓resolved
Trevor McKay

_mogrify leaks reference when same dict value referenced multiple times with $()

Reported by Trevor McKay | December 5th, 2011 @ 03:49 PM

Discovered in 2.0.13, verified against 2.4.3 from git.

Note, title is wrong, I typed $() instead of %() but I can't find a way to fix it....

If _mogrify is called with an operation string and a dictionary and the operation string references a value from the dict using the %() syntax more than once, a reference to that dict value will be leaked for each reference after the first.

I attached a (very simple) patch for this wich fixes the problem, however being unfamiliar with the code it may not be correct from a wholistic perspective :) Please advise.

We at Red Hat are carrying psycopg2 2.0.13 and 2.0.14 in RHEL 5 and RHEL 6, and it is being packaged at Fedora as well (2.4.2 in F15, in F15+ also I believe). If someone can verify that the patch is legit and approve it, that would be great -- we can carry our own patch until it's available upstream.

I can also attach a simple test program which demonstrates the problem (I assume the bug system will let me submit an additional attachment after creation).

Comments and changes to this ticket

  • Trevor McKay

    Trevor McKay December 5th, 2011 @ 03:52 PM

    Note, the test program assumes a local database with the dsn ""dbname=cumin user=cumin host=localhost" just to get a connection so a cursor can be created. Modify as necessary, the call to mogrify is the important part.

  • Trevor McKay

    Trevor McKay December 9th, 2011 @ 08:59 PM


    I found a patch for this already in version 2.3.2, but it appears not to be in the 2.4 tree (fyi).

  • Daniele Varrazzo

    Daniele Varrazzo December 11th, 2011 @ 02:53 AM

    • State changed from “new” to “resolved”

    Good catch, thank you very much. Fixed in my devel.

    What do you mean as "found a patch in 2.3.2"?

  • Trevor McKay

    Trevor McKay December 12th, 2011 @ 02:09 PM

    What do you mean as "found a patch in 2.3.2"

    Sorry for the confusion on this. It appears that at least some Fedora and/or Red Hat distributions of psycopg2 have applied the fix for this in the past, but maybe the fix wasn't pushed back to upstream (or maybe it was lost, another possibility?). I didn't realize this until after I posted the comment :)

    Still trying to sort out the history on our end, thank you for the fix.


  • Trevor McKay

    Trevor McKay December 12th, 2011 @ 03:26 PM


    Just to be clear for posterity. I was mistaken about any patch in 2.3.2, the error is there is well.

    The code in 2.3.2 is using "item = PyObject_GetItem(n, key)" to check for presence of the value in the temporary dictionary, and so it rightly contains "Py_DECREF(item)" in the case where the value is found to already be in the dictionary. What it is missing is another call, Py_DECREF(value).

    In newer versions, "item = PyObject_GetItem(n, key)" is replaced with "0 == PyDict_Contains(n, key)", so there is no "item". It turns out that the call "Py_DECREF(value)" goes in the code at the same place where "Py_DECREF(item)" used to be in older versions :)

    So, after looking at newer code and applying the fix, I looked at 2.3.2 and my brain saw what it was expecting to see instead of what was. Being late afternoon on Friday made it worse... haha

  • Daniele Varrazzo

    Daniele Varrazzo December 12th, 2011 @ 03:53 PM

    Oh, I see what you mean. I've checked if the error was introduced in the commit 99b3c723 (where the PyDict_Contains was introduced) but it's been instead in psycopg since ever... It was probably in psycopg 1 too.

    Thank you again for the catch, and it was just in time for the release of 2.4.3: great!

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Psycopg is the most used PostgreSQL adapter for the Python programming language. At the core it fully implements the Python DB API 2.0 specifications. Several extensions allow access to many of the features offered by PostgreSQL.

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