Tips: resource limits in OpenDJ

Photo by Scallop Holden http://www.flickr.com/photos/scallop_holden/

OpenDJ, the open source LDAP directory services in Java, defines a few global resource limits to prevent client connections or operations from abusing the server’s resources. These limits are

• the maximum number of entries returned to a search request (size-limit, default is 1000),
• the maximum amount of time to spend returning results to a client (time-limit, default is 60 seconds),
• the maximum number of entries to look through while processing a search request (lookthrough-limit, default is 5000),
• the maximum amount of time a connection can sit idle before the server disconnect it (idle-time-limit, default is unlimited).

There are default values for all of these limits in the Global configuration, but they can also be set on a per user basis. The global limits are read or set using dsconfig :

$ bin/dsconfig get-global-configuration-prop -p 4444 -X -n -h localhost \
 -D cn=directory\ manager -w secret12
Property : Value(s)
--------------------------------------:------------------------
bind-with-dn-requires-password : true
default-password-policy : Default Password Policy
disabled-privilege : -
entry-cache-preload : false
etime-resolution : milliseconds
idle-time-limit : 0
lookthrough-limit : 5000
max-allowed-client-connections : 0
max-psearches : unlimited
proxied-authorization-identity-mapper : Exact Match
reject-unauthenticated-requests : false
return-bind-error-messages : false
save-config-on-successful-startup : true
size-limit : 1000
smtp-server : -
time-limit : 60 s
writability-mode : enabled

The per user limits have a different LDAP attribute name and can be found or set directly in users’ entry, or through Collective Attributes. The Directory Manager entry has such specific limits set, so that everything is unlimited.

$ bin/ldapsearch -D "cn=directory manager" -w secret12 -p 1389 -X -b "cn=config" \
  '(objectClass=inetOrgPerson)' ds-rlim-time-limit ds-rlim-size-limit \
  ds-rlim-lookthrough-limit ds-rlim-idle-time-limit
dn: cn=Directory Manager,cn=Root DNs,cn=config
ds-rlim-lookthrough-limit: 0
ds-rlim-time-limit: 0
ds-rlim-idle-time-limit: 0
ds-rlim-size-limit: 0

If you decide to change the default global settings, for example the idle-time-limit, to force idle connections to be closed by the server after some time (often a smaller time than the settings of the load-balancer in between your applications and the OpenDJ servers), please remember that you might also want to change the limit for “cn=Directory Manager”, especially if your client applications are connecting with Directory Manager credentials.

An important tuning flag for OpenDJ with 64bit JVM…

If you’re running OpenDJ with a 64bit JVM with less than 32GB of heap size, be aware of the need to explicitly set the -XX:+UseCompressedOops option (unless you want to disable it).

Compressed oops is supported and enabled by default in Java SE 6u23 and later, when running a 64bit JBM with a value of -Xmx lower than 32GB. You can find more information about Compressed Oops in Java technical notes here: http://download.oracle.com/javase/7/docs/technotes/guides/vm/performance-enhancements-7.html

However, OpenDJ internal database, in order to estimate properly the occupation of the DB cache and tune the cache eviction threads, needs to take into account the compressed oops option. For this is relies on the JVM option to be set explicitly. If the option is not explicitly set, the database may consider the cache full when it’s not, and run cache eviction too early, resulting in less optimized performances.

So, with 64bit JVM, make sure you add the -XX:+UseCompressedOops option to the start-ds line in the config/java.properties file. Then run bin/dsjavaproperties and restart OpenDJ to benefit from the new settings.

OpenDJ: Analyzing Search Filters and Indexes

LDAP directory services greatly rely on indexes to provide fast and accurate search results.

OpenDJ, the open source LDAP directory services for the Java platform, provides a number of tools to ensure indexes are efficiently used or to optimize them for even better performances.

To start with, OpenDJ rejects by default all unindexed searches, unless the authenticated user has the privilege to perform them. Unindexed searches are rejected because they result in scanning the whole database, which consumes lots of resources and time. There are legitimate uses of unindexed search though, and OpenDJ offers a way to control who can perform them through a privilege. To learn more about privileges, how to grant them, please check the Administration Guide or some of my previous posts.

When unindexed searches are completed, OpenDJ (starting with revision 7148 of the OpenDJ trunk, and therefore OpenDJ 2.5) does logs the “Unindexed” keyword as part of the Search Response access log message. But the access log file can also be used to identify search operations that are not making an optimal use of indexes. Simply check for those search responses that have been returned with an etime (execution time) greater than the average.

The access log example below contains both an unusually high etime (expressed in ms) and the Unindexed tag.

[27/Jul/2011:20:27:27 +0200] SEARCH RES conn=0 op=1 msgID=2 result=0 nentries=10001 Unindexed etime=1846

The verify-index command let you check that no index is corrupted (i.e. no data is missing from indexes).

The rebuild-index command let you build or rebuild an index that would be corrupted or had its configuration changed.

One of the tuning parameter of indexes is the index-entry-limit (which was known in Sun DSEE as the AllIDsThreshold), the maximum size of entries kept in an index record, before the server stop maintaining that record and consider it’s more efficient to scan the whole database. For more information on the index entry limit, check the Section 7.2.4 Changing Index Entry Limits of the Indexing chapter of the Administration Guide.

OpenDJ provides a static analyzer of indexes which can help to understand how well the attributes are indexed, as well as help to tune the index entry limit. This tool is a function of the dbtest utility and is simply used as follow:

$ bin/dbtest list-index-status -n userRoot -b "dc=example,dc=com"

Index Name Index Type JE Database Name Index Valid Record Count Undefined 95% 90% 85%

---------------------------------------------------------------------------------------------------------------------------------------
id2children                Index       dc_example_dc_com_id2children                true         2             0          0    0    0
id2subtree                 Index       dc_example_dc_com_id2subtree                 true         2             0          0    0    0
uid.equality               Index       dc_example_dc_com_uid.equality               true         2000          0          0    0    0
aci.presence               Index       dc_example_dc_com_aci.presence               true         0             0          0    0    0
ds-sync-conflict.equality  Index       dc_example_dc_com_ds-sync-conflict.equality  true         0             0          0    0    0
givenName.equality         Index       dc_example_dc_com_givenName.equality         true         2000          0          0    0    0
givenName.substring        Index       dc_example_dc_com_givenName.substring        true         5777          0          0    0    0
objectClass.equality       Index       dc_example_dc_com_objectClass.equality       true         6             0          0    0    0
member.equality            Index       dc_example_dc_com_member.equality            true         0             0          0    0    0
uniqueMember.equality      Index       dc_example_dc_com_uniqueMember.equality      true         0             0          0    0    0
cn.equality                Index       dc_example_dc_com_cn.equality                true         2000          0          0    0    0
cn.substring               Index       dc_example_dc_com_cn.substring               true         19407         0          0    0    0
sn.equality                Index       dc_example_dc_com_sn.equality                true         2000          0          0    0    0
sn.substring               Index       dc_example_dc_com_sn.substring               true         8147          0          0    0    0
telephoneNumber.equality   Index       dc_example_dc_com_telephoneNumber.equality   true         2000          0          0    0    0
telephoneNumber.substring  Index       dc_example_dc_com_telephoneNumber.substring  true         16506         0          0    0    0
ds-sync-hist.ordering      Index       dc_example_dc_com_ds-sync-hist.ordering      true         1             0          0    0    0
mail.equality              Index       dc_example_dc_com_mail.equality              true         2000          0          0    0    0
mail.substring             Index       dc_example_dc_com_mail.substring             true         7235          0          0    0    0
entryUUID.equality         Index       dc_example_dc_com_entryUUID.equality         true         2002          0          0    0    0

Total: 20

If an index contains a non zero value (N) in the undefined column, it means N index keys have reached the index entry limit and are no longer maintained. This can be normal, for example with the ObjectClass equality index, where the vast majority of entries will have the same objectclasses (top, Person, organizationalPerson, inetOrgPerson). But, for other attributes, such as cn, it may indicate that the index entry limit is too low.

Finally, OpenDJ has an option to do a live analysis of search filters and how they use indexes. To enable live index analysis, simply enable it for the database backend that contains the data :

dsconfig set-backend-prop --backend-name userRoot  --set index-filter-analyzer-enabled:true \
 --set max-entries:50 -h localhost -p 4444 -D cn=Directory\ Manager -w ****** -n -X

The max-entries parameter specifies how many filter items are being analyzed and kept in memory. Only the last max-entries will be kept. If there is a huge variety of requests against the directory service, you might want to increase the number. However, keep in mind that the analysis is kept in memory, and the higher the number the largest the impact on the overall performances of the server.

We do not recommend that you leave the index analysis enabled all the time, especially in production. The index analyzer should be used to gather statistics over a flow of requests for a short period of time, and should be disabled afterwards to free the resources.

The result of the index analyzer can be retrieved under the cn=monitor suffix, more specifically as part of the database environment of the backend.

$ bin/ldapsearch -p 1389 -D cn=directory\ manager -w secret12  \
-b "cn=userRoot Database Environment,cn=monitor" '(objectclass=*)' filter-use

dn: cn=userRoot Database Environment,cn=monitor
filter-use: (uid=user.*) hits:1 maxmatches:20 message:
filter-use: (tel=*) hits:1 maxmatches:-1 message:presence index type is disabled
  for the tel attribute
filter-use: (objectClass=groupOfURLs) hits:1 maxmatches:0 message:
filter-use: (objectClass=groupOfEntries) hits:1 maxmatches:0 message:
filter-use: (objectClass=person) hits:1 maxmatches:20 message:
filter-use: (objectClass=ds-virtual-static-group) hits:1 maxmatches:0 message:
filter-use: (aci=*) hits:1 maxmatches:0 message:
filter-use: (objectClass=groupOfNames) hits:1 maxmatches:0 message:
filter-use: (objectClass=groupOfUniqueNames) hits:1 maxmatches:0 message:
filter-use: (objectClass=ldapSubentry) hits:1 maxmatches:0 message:
filter-use: (objectClass=subentry) hits:1 maxmatches:0 message:

hits represents the number of time this filter was used. the maxmatches represents the maximum number of entries that were returned for that filter.

Index analysis and tuning is not a simple task, and I recommend to play with these tools  a lot on a test environment to understand how to get the best out of them. But, as you can see, OpenDJ provides you with all the tools you need to get the best performances out of your LDAP directory.