[email protected] wrote: > Full_Name: Steven Lang > Version: LMDB 0.9.16 > OS: Ubuntu 14.04 > URL: ftp://ftp.openldap.org/incoming/steven-lang-150929.c > Submission from: (NULL) (199.255.44.5) > > > While doing some testing using randomized key and data lengths and random puts > and deletes, I found a situation in which mdb_cursor_del(...) followed by > mdb_cursor_get(..., MDB_NEXT) causes an error: > > mdb.c:5726: Assertion 'IS_LEAF(mp)' failed in mdb_cursor_next() > Aborted > > After a little debugging I was able to isolate what the cause was and produce > a > simple program to reproduce the issue; during the re-balance following a > delete, > it would try to move a node from the first child of the root page to the > second. > If the node it moves has a key longer than the second node in the root page, > and > the new key doesn't fit, it will split the root page. As a result, by > deleting a > node, the tree becomes deeper. > > However, the cursor only checks and compensates for the tree becoming > shallower. > So now the cursor was pointing to a branch page rather than a leaf page. Any > further cursor operations fail. (Trying to do a MDB_SET, MDB_SET_RANGE, etc > will > silently fail at this point, while MDB_NEXT and possibly MDB_PREV will > assert.) > > The latest head with the fix for ITS#8221 changes the behavior slightly, due > to > the different arrangement of the tree with the less aggressive merging. > However, > it still fails. > > Attached is a program which fills a DB, then deletes keys until it asserts.
Thanks for the report. Our alternate approach to solve #8221 was to check the page fill factor including the (usually omitted) key #0 size; we didn't go that way because it was slightly more processing. But given this bug, it seems that's the only way to go. -- -- Howard Chu CTO, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc/ Chief Architect, OpenLDAP http://www.openldap.org/project/
