Luke Kenneth Casson Leighton wrote:

hi all,

the infamous obscure error which people are seeing only very infrequently is rearing its head at least 2 to 3 times per day in a test lab where i work. this is however a secure environment so i cannot post core-dumps or any details of the application.

given the restrictions, what information is needed and what approach is needed to debug and fix this? luckily it's happening a lot so there's the possibility of a regular iterative approach.

the operating system(s) have been ubuntu 12.04 and also 14.04, both have resulted in this obscure bug. bizarrely, this bug occurs in a *single process*. it's not even multi-processing. however metasync=False, sync=False, map_async=True, readahead=False and writemap=True.

Use the Source, Luke.

MDB_BAD_RSLOT is returned only one place in mdb.c and the situation is very specific. It means you've tried to begin a new read txn on a thread that already has a read txn outstanding. The API docs are pretty clear that a thread may only have one txn at a time.

You need to track down whatever is creating read txns in your code and make sure they're being properly committed or aborted.