In openldap-technical, Quanah Gibson-Mount wrote: > As per Howard Chu (Author of MDB, Primary OpenLDAP Developer): > > ------------------------------------------------------------- > Full details are in the paper. > http://www.openldap.org/pub/hyc/mdm-paper.pdf > > MDB assumes a unified buffer cache. See section 3.1, references 17, 18, and > 19. > > Note that this requirement can be relaxed in the current version of the > library. If you create the environment with the MDB_WRITEMAP option then > all reads and writes are performed using mmap, so the file buffer cache is > irrelevant. Of course then you lose the protection that the read-only map > offers. That's not quite true. mdb_env_open() does a read() of the meta pages. I presume this can only be a problem when other processes have the database open? In that situation, I think the read() can be avoided by maintaining a copy of the relevant MDB_meta information in the lock file. The read() only needs enough info to know how to map the data file. This would require a version increase for the lock file and programs using it, but not for the database file.