OpenLDAP MDB vs HDB performance

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Article Information
This article applies to the following ZCS versions. 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. Tests were done using OpenLDAP 2.4.34.

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.

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
hdb-shm: 12m4.885s

Advantage: MDB. It is 51.73 times faster than hdb at performing 28,000 modifications.

Master node

mdb: 0m20.628s
hdb: 25m46.477s
hdb-shm: 24m39.658s

Advantage: MDB. It is 71.73 times faster than hdb at performing 28,000 modifications.

Master node accesslog DB sizes

mdb: 100M
hdb: 234M
hdb-shm: 234MB

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

Read Performance

• Read performance is examined on my blog: MDB vs HDB performance