Re: LMDB: issue with mdb_cursor_del

[Howard Chu <hyc@symas.com>]

timur.kristof@gmail.com wrote:
> Hi,
>
> I have an app that uses LMDB, and I've experienced an interesting
> issue: when trying to delete a certain item with mdb_cursor_del, it
> crashed with the following backtrace: https://pastebin.com/7p9wtkj9
>
> It appears that it couldn't mark a page as dirty.
> Here is the relevant assertion from mdb_page_dirty:
> rc = insert(txn->mt_u.dirty_list, &mid);
> mdb_tassert(txn, rc == 0); // assertion failed
>
> What might I be doing wrong in my application that triggers this sort
> of error?

Take a look at the value of rc, then look in midl.c. Most likely the dirty 
list is too big, which means you're trying to do too much in a single transaction.

> Also interesting:
> The database was about 60MB, and I now compacted it using mdb_copy -c.
> Now it is only ~6MB, and running the app with the compacted database,
> the above error also disappeared.
>
> I'm not sure why the compacting fixed the problem, could somebody offer
> an insight about this?
>
> Thank you guys in advance for your answers!
> Best regards,
> Timur


--
  -- Howard Chu
  CTO, Symas Corp.           http://www.symas.com
  Director, Highland Sun     http://highlandsun.com/hyc/
  Chief Architect, OpenLDAP  http://www.openldap.org/project/