A template is defined by a filter string and an index identifying a set of attributes. The template string for a query can be obtained by removing assertion values from the RFC 4515 representation of its search filter. A query belongs to a template if its template string and set of projected attributes correspond to a cacheable template. Examples of template strings are (mail=), (|(sn=)(cn=)), (&(sn=)(givenName=)).

The config directives that are specific to the proxycache overlay can be prefixed by proxycache- , to avoid conflicts with directives specific to the underlying database or to other stacked overlays. This may be particularly useful for those directives that refer to the backend used for local storage. The following cache specific directives can be used to configure the proxy cache:

overlay pcache This directive adds the proxy cache overlay to the current backend. The proxy cache overlay may be used with any backend but is intended for use with the ldap , meta , and sql backends.

proxycache <database> <max_entries> <numattrsets> <entry_limit> <cc_period> The directive enables proxy caching in the current backend and sets general cache parameters. A <database> backend will be used internally to maintain the cached entries. The chosen database will need to be configured as well, as shown below. Cache replacement is invoked when the cache size grows to <max_entries> entries and continues till the cache size drops below this size. <numattrsets> should be equal to the number of following proxyattrset directives. Queries are cached only if they correspond to a cacheable template (specified by the proxytemplate directive) and the number of entries returned is less than <entry_limit>. Consistency check is performed every <cc_period> duration (specified in secs). In each cycle queries with expired "time to live(TTL)" are removed. A sample cache configuration is:

proxycachequeries <queries> Specify the maximum number of queries to cache. The default is 10000.

proxysavequeries { TRUE | FALSE } Specify whether the cached queries should be saved across restarts of the caching proxy, to provide hot startup of the cache. Only non-expired queries are reloaded. The default is FALSE. CAVEAT : of course, the configuration of the proxycache must not change across restarts; the pcache overlay does not perform any consistency checks in this sense. In detail, this option should be disabled unless the existing proxyattrset and proxytemplate directives are not changed neither in order nor in contents. If new sets and templates are added, or if other details of the pcache overlay configuration changed, this feature should not be affected.

proxyattrset <index> <attrs...> Used to associate a set of attributes <attrs..> with an <index>. Each attribute set is associated with an integer from 0 to <numattrsets>-1. These indices are used by the proxytemplate directive to define cacheable templates. A set of attributes cannot be empty. A set of attributes can contain the special attributes "*" (all user attributes), "+" (all operational attributes) or both; in the latter case, any other attribute is redundant and should be avoided for clarity. A set of attributes can contain "1.1" as the only attribute; in this case, only the presence of the entries is cached.

proxytemplate <template_string> <attrset_index> <ttl> [<negttl> [<limitttl>]] Specifies a cacheable template and "time to live" <ttl> of queries belonging to the template. An optional <negttl> can be used to specify that negative results (i.e., queries that returned zero entries) should also be cached for the specified amount of time. Negative results are not cached by default (<negttl> set to 0). An optional <limitttl> can be used to specify that results hitting a sizelimit should also be cached for the specified amount of time. Results hitting a sizelimit are not cached by default (<limitttl> set to 0).

response-callback { head | tail } Specifies whether the response callback should be placed at the tail (the default) or at the head (actually, wherever the stacking sequence would make it appear) of the callback list. This affects how the overlay interacts with other overlays, since the proxycache overlay should be executed as early as possible (and thus configured as late as possible), to get a chance to return the cached results; however, if executed early at response, it would cache entries that may be later "massaged" by other databases and thus returned after massaging the first time, and before massaging when cached.

There are some constraints: all values must be positive; <entry_limit> must be less than or equal to <max_entries> ; <numattrsets> attribute sets SHOULD be defined by using the directive proxyattrset ; all attribute sets SHOULD be referenced by (at least) one proxytemplate directive;

The following adds a template with filter string (&(sn=)(givenName=)) and attributes mail, postaladdress, telephonenumber and a TTL of 1 hour.

proxyattrset 0 mail postaladdress telephonenumber
proxytemplate (&(sn=)(givenName=)) 0 3600

Directives for configuring the underlying database must also be given, as shown here:

directory /var/tmp/cache
cachesize 100

Any valid directives for the chosen database type may be used. Indexing should be used as appropriate for the queries being handled. In addition, an equality index on the queryid attribute should be configured, to assist in the removal of expired query data.

ETCDIR/slapd.conf default slapd configuration file