OpenLDAP MDB vs HDB performance

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Article Information

This article applies to the following ZCS versions.

ZCS 8.0 Article ZCS 8.0

Zimbra OpenLDAP Server

Performance differences between the mdb and hdb backends for OpenLDAP

Using real-world client data, I've compiled some brief performance differences between using the mdb and hdb backends to OpenLDAP with Zimbra. This particular client has 25,208 entries in their LDAP database. I dumped their accesslog and converted it to LDIF to give me a full weeks worth of real change data, and then ran that back against the database. This results in approximately 28,000 modifications performed against the DB.

Database configuration information

The following documents the pertinent configuration information for MDB and HDB.

MDB configuration

For MDB, the following database flags were set:

writemap
nometasync

HDB configuration

For both single node and master node tests, hdb had a 1GB cache defined via DB_CONFIG. This was more than sufficient for the DB in all tests. Two sets of tests were done, one with a shared memory key for BDB, and one without. The back-hdb database was configured to fully cache all entries (cachesize, idlcachesize settings for cn=config).

Database load

This is the amount of time to load the database using slapadd -q

mdb: 0m11.237s
hdb: 0m38.727s
hdb-shm: 0m26.677s

Advantage: MDB. It is at least 2.37 times faster loading the data than hdb.

Database size

Size of database on disk after slapadd completes. For hdb, this includes the hdb cache as well as db size. mdb has no cache.

mdb: 296MB
hdb: 627MB
hdb-shm: 627MB

Advantage: MDB. It is 2.11 times smaller than the hdb database.

Search time

This is the time to search the entire db via ldapsearch. Note that with hdb, since it has to preload the cache, two times are given. cold (Cache not loaded) and hot (cache loaded). mdb never needs to preload the cache.

mdb: 0m1.435s
hdb cold: 0m5.304s
hdb hot: 0m3.103s
hdb-shm cold: 0m5.220s
hdb-shm hot: 0m1.472s

Advantage MDB. It is 1.03 times faster than hdb on the hot hdb search when hdb uses SHM keys. Note that hdb performance degrades as the number of concurrent searches increases, while mdb performance is static.

Write performance

The following write performance was done with the 28,000 modification LDIF described above. It was done two ways -- Single node (no replication setup) and Master node (accesslog delta-sync database enabled). Time to do all 28,000 modifications is tracked. In the master node scenario, the size of the resulting accesslog DB is also compared.

Single node

mdb: 0m14.013s
hdb: 13m3.394s

Advantage: MDB. It is 55.90 times faster than hdb at performing 28,000 modifications.

Master node

mdb: 0m20.628s
hdb: 25m46.477s

Advantage: MDB. It is 74.97 times faster than hdb at performing 28,000 modifications.

Master node accesslog DB sizes

mdb: 100M
hdb: 234M

Advantage: MDB. It is 2.34 times smaller than the hdb accesslog DB.

Verified Against: ZCS 8.0 Date Created: 2/21/2013
Article ID: https://wiki.zimbra.com/index.php?title=OpenLDAP_MDB_vs_HDB_performance Date Modified: 2013-03-04



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