Chapter 6. Managing the Database Cache Settings
Directory Server uses the following caches:
- The Entry cache, which contains individual directory entries.
- The DN cache is used to associate DNs and RDNs with entries.
- The Database cache, which contains the database index files
*.dband*.db4files.
For the highest performance improvements, all cache sizes must be able to store all of their records. If you do not use the recommended auto-sizing feature and have not enough RAM available, assign free memory to the caches in the previously shown order.
6.1. The Database and Entry Cache Auto-Sizing Feature
By default, Directory Server automatically determine the optimized size for the database and entry cache. Auto-sizing optimizes the size of both caches based on the hardware resources of the server when the instance starts.
Important
Red Hat recommends to use the auto-tuning settings. Do not set the entry cache size manually.
6.1.1. Manually Re-enabling the Database and Entry Cache Auto-sizing
If you upgraded the instance from a version prior to 10.1.1, or previously manually set an entry cache size, you can enable the auto-tuning for the entry cache.
The following parameters in the
cn=config,cn=ldbm database,cn=plugins,cn=config entry control the auto-sizing:
nsslapd-cache-autosize- This settings controls if auto-sizing is enabled for the database and entry cache. Auto-sizing is enabled:
- For both the database and entry cache, if the
nsslapd-cache-autosizeparameter is set to a value greater than0. - For the database cache, if the
nsslapd-cache-autosizeandnsslapd-dbcachesizeparameters are set to0. - For the entry cache, if the
nsslapd-cache-autosizeandnsslapd-cachememsizeparameters are set to0.
nsslapd-cache-autosize-split- The value sets the percentage of RAM that is used for the database cache. The remaining percentage is used for the entry cache.Using more than 1.5 GB RAM for the database cache does not improve the performance. Therefore, Directory Server limits the database cache 1.5 GB.
To enable the database and entry cache auto-sizing:
- Stop the Directory Server instance:
# systemctl stop dirsrv@instance_name
- Backup the
/etc/dirsrv/slapd-instance_name/dse.ldiffile:# cp /etc/dirsrv/slapd-instance_name/dse.ldif \ /etc/dirsrv/slapd-instance_name/dse.ldif.bak.$(date "+%F_%H-%M-%S") - Edit the
/etc/dirsrv/slapd-instance_name/dse.ldiffile:- Set the percentage of free system RAM to use for the database and entry cache. For example, to set 10%:
nsslapd-cache-autosize: 10
Note
If you set thensslapd-cache-autosizeparameter to0, you must additionally set:- the
nsslapd-dbcachesizein thecn=config,cn=ldbm database,cn=plugins,cn=configentry to0to enable the auto-sized database cache. - the
nsslapd-cachememsizein thecn=database_name,cn=ldbm database,cn=plugins,cn=configentry to0to enable the auto-sized entry cache for a database.
- Optionally, set the percentage used from the free system RAM for the database cache. For example, to set 40%:
nsslapd-cache-autosize-split: 40
Directory Server uses the remaining 60% of free memory for the entry cache. - Save the changes.
- Start the Directory Server instance:
# systemctl start dirsrv@instance_name
Example 6.1. The nsslapd-cache-autosize and nsslapd-cache-autosize-split Parameter
The following settings are the default values for the parameters:
nsslapd-cache-autosize: 25 nsslapd-cache-autosize-split: 25 nsslapd-dbcachesize: 1536MB
Using these settings, 25% of the system's free RAM is used (
nsslapd-cache-autosize). From this memory, 25% are used for the database cache (nsslapd-cache-autosize-split) and the remaining 75% for the entry cache.
Depending on the free RAM, this results in the following cache sizes:
|
GB of Free RAM
|
Database Cache Size
|
Entry Cache Size
|
|---|---|---|
|
1 GB
|
64 MB
|
192 MB
|
|
2 GB
|
128 MB
|
384 MB
|
|
4 GB
|
256 MB
|
768 MB
|
|
8 GB
|
512 MB
|
1,536 MB
|
|
16 GB
|
1,024 MB
|
3,072 MB
|
|
32 GB
|
1,536 MB
|
6,656 MB
|
|
64 GB
|
1,536 MB
|
14,848 MB
|
|
128 GB
|
1,536 MB
|
31,232 MB
|
