On Mon, Sep 25, 2023 at 05:37:00PM +0200, Branko Čibej wrote: > IIRC, Berkeley DB multi-process concurrency is managed through an on-disk > "register" file external to the actual key/value store. The key/value store > format is not affected by the presence of this file. The DB_REGISTER > mechanism was introduced in BDB 4.4 (now long defunct) and can be used for > both concurrency control and automatic database recovery. The client-side > code for this can be lifted from Subversion. > > (I was involved in designing this mechanism for BDB and implementing its use > in Subversion, but that was ages ago -- back in 2005. There may be better > ways do do this in newer versions of Berkeley DB). > > TL;DR: all upstream supported versions of BDB should have this mechanism > available and APR can detect if it's being used without changing the API, > and even "upgrade" existing databases with the register file on the fly > without affecting the actual database.
Thanks a lot for the response Branko, this is helpful. I spent a lot more time playing with this and I can get apr_dbm to use a DB_ENV in the way you suggest with locking. However, the path handling becomes very complicated/impossible - with a DB_ENV the database is assumed to be inside the "db_home" directory but we want to load/save a database by absolute path name. Using BDB in this way also appears incompatible with apr_dbm since the _usednames API assumes that at most two state files are used and with a full BDB environment the state is a whole directory. (mod_dav relies on this feature working correctly) So I don't want to appear like I'm shrugging this off but *at best* it might be possible to fix BDB for some versions (possibly, in theory, with compat concerns), and that leaves older BDB releases plus NDBM still broken. As an httpd developer I really don't care about database internals, I just want this to work. I also know that Berkeley DB is deprecated and will be removed from my Linux distribution of choice, so I don't want to invest too much time in it. :( Regards, Joe
