Re: MDB_MAP_FULL with plenty of free pages

Michael Ströder wrote: Yes it makes no difference since by default, back-mdb stores all entries as single blobs. Thus the entire entry is always rewritten on any modification. LMDB stores all records as a single contiguous set of pages, so the larger the entry, the more contiguous pages it needs for storing them. Since the free page manager in LMDB is extremely simplistic, it doesn't do well with random allocations and deallocations of widely varying sizes, and so over time the free space fragmentation gets worse, resulting in spans of pages that are too small to service the requests for the larger entries. The multival feature in OpenLDAP 2.5 back-mdb lets you configure some attributes to have their values stored as individual DB records, which then means that modifications of individual values don't have to rewrite the entire entry. And with smaller records, the fragmentation issue goes away. The tradeoff of course is that it takes multiple DB accesses to construct an entry, so write performance improves at the cost of read performance. There's no free lunch... -- -- Howard Chu CTO, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc/ Chief Architect, OpenLDAP http://www.openldap.org/project/