del db does actually not release the LOCK

[oleiade]

While trying to port plyvel into Elevator, I noticed that DB.del method does not actually release the LOCK.

>>> db = plyvel.DB('default')
>>> del db
>>> new_db = plyvel.DB('default')
---------------------------------------------------------------------------
IOError                                   Traceback (most recent call last)
<ipython-input-10-7174fcd34511> in <module>()
----> 1 new_db = plyvel.DB('default')

/Users/oleiade/.python-eggs/plyvel-0.1dev-py2.7-macosx-10.8-intel.egg-tmp/plyvel/_plyvel.so in plyvel._plyvel.DB.__init__ (plyvel/_plyvel.cpp:2264)()

/Users/oleiade/.python-eggs/plyvel-0.1dev-py2.7-macosx-10.8-intel.egg-tmp/plyvel/_plyvel.so in plyvel._plyvel.raise_for_status (plyvel/_plyvel.cpp:1061)()

IOError: IO error: lock default/LOCK: already held by process

[oleiade]

My bad, bug seems to be inherent to my macbook dev environment rather than plyvel.

[wbolster]

I'm seeing similar issues, actually. Any clue on what might be causing this?

[wbolster]

Is the example you gave above a complete example? Did you execute any operations in between that may have resulted in references to iterators or write batches still lying around (note that write batches in a "with" block will not be deallocated automatically)?

[oleiade]

Hey, it kind of reassure me at least that you get the same problem too, 'cause I started seing it on another computer running freebsd today.

Yes this is a complete sample.

I've noticed that through unit tests, and went down to the minimal operation of creating a db connector -> releasing it -> creating a new connector to that db; which raises the problem.

[oleiade]

Tested on Linux mint, this passes:

>>> import plyvel
>>> db = plyvel.DB('default')
>>> new_db = plyvel.DB('default')
>>> db.put('1', 'a')
>>> new_db.get('1')

So I guess that in some way, python/cython, makes it possible for two DB objects working on the same db, in the same process to share the DB* pointer. (Don't ask me how, this is just an hypothesis).

On what os, python version etc did you experienced that bug?

[wbolster]

The double open support is a LevelDB bug I think. I guess it can lead to corruption even.

[wbolster]

I'm working on DB.close() btw, but it's a bit tricky due to the way things like iterator destructors work. And it requires a check in each public API method. :-(

[wbolster]

Btw, the double open issue does not reuse the pointer I think.

[wbolster]

It took some effort, but here we are: plyvel.DB has a .close () method since commit 755e000. Please review and test, since the code is a bit tricky. (Don't forget to check the API docs.)

[wbolster]

Did you have any chance to test whether the .close() API solves the problems reported earlier?

[wbolster]

Btw, the double open issue has been fixed a while back in LevelDB itself: http://code.google.com/p/leveldb/issues/detail?id=120

[oleiade]

Problem seems to be solved now.
With plyvel head at fccb583 and leveldb 1.7.1

[wbolster]

Ok, same here. Thanks for the report.