266 means a call to open() returned ENOENT. Typo in the directory name? AFAICT you're not doing anything wrong. That assert() failing most likely indicates some problem in the LSM incremental merge code. But it might also be a problem in the compression wrappers, or something in the host app (i.e. heap corruption). Assuming it is an LSM bug it will be subtle - or it would have shown up in testing already. To fix this I need some way to reproduce the problem locally. Are you able to create a C program, or a python script, or an SQL script for the shell tool (or anything really) that does that? We already have tests for "big databases that use compression" - so I suspect if I just try to go fishing for the bug it might take quite a while... Cheers, Dan.