# $OpenLDAP$
-# Copyright 2003, The OpenLDAP Foundation, All Rights Reserved.
+# Copyright 2003-2005, The OpenLDAP Foundation, All Rights Reserved.
# COPYING RESTRICTIONS APPLY, see COPYRIGHT.
H1: The Proxy Cache Engine
H2: Overview
-The proxy cache extension of slapd handles a search request (query)
+The proxy cache extension of slapd is designed to improve the
+responseiveness of the ldap and meta backends. It handles a search
+request (query)
by first determining whether it is contained in any cached search
filter. Contained requests are answered from the proxy cache's local
-database.
+database. Other requests are passed on to the underlying ldap or
+meta backend and processed as usual.
E.g. {{EX:(shoesize>=9)}} is contained in {{EX:(shoesize>=8)}} and
{{EX:(sn=Richardson)}} is contained in {{EX:(sn=Richards*)}}
belongs to one of these templates. The entries corresponding to
cached queries are stored in the proxy cache local database while
its associated meta information (filter, scope, base, attributes)
-is stored in main memory. Instead of sending a referral for requests
-which are not contained, it acts as a proxy and obtains the result
-by querying one or more target servers. The proxy cache extends the
-meta backend and uses it to connect to target servers.
+is stored in main memory.
A template is a prototype for generating LDAP search requests.
Templates are described by a prototype search filter and a list of
The cache replacement policy removes the least recently used (LRU)
query and entries belonging to only that query. Queries are allowed
a maximum time to live (TTL) in the cache thus providing weak
-consistency. A background thread periodically checks the cache for
+consistency. A background task periodically checks the cache for
expired queries and removes them.
The Proxy Cache paper
H2: Proxy Cache Configuration
The cache configuration specific directives described below must
-appear after {{EX:overlay proxycache}} directive within a
+appear after a {{EX:overlay proxycache}} directive within a
{{EX:"database meta"}} or {{EX:database ldap}} section of
the server's {{slapd.conf}}(5) file.
> proxyCache <DB> <maxentries> <nattrsets> <entrylimit> <period>
-The directive enables proxy caching and sets general cache parameters.
+This directive enables proxy caching and sets general cache parameters.
The <DB> parameter specifies which underlying database is to be
used to hold cached entries. It should be set to {{EX:bdb}},
{{EX:hdb}}, or {{EX:ldbm}}. The <maxentries> parameter specifies
the total number of entries which may be held in the cache. The
<nattrsets> parameter specifies the total number of attribute sets
-(as specified by the {{EX:proxyAttrSet}} directive) may be defined.
+(as specified by the {{EX:proxyAttrSet}} directive) that may be defined.
The <entrylimit> parameter specifies the maximum number of entries
-in a cachable query. The <period> specifies the duration consistency
+in a cachable query. The <period> specifies the consistency
check period (in seconds). In each period, queries with expired
TTLs are removed.
Used to associate a set of attributes to an index. Each attribute
set is associated with an index number from 0 to <numattrsets>-1.
-These indices are used by the addtemplate directive to define
+These indices are used by the proxyTemplate directive to define
cacheable templates.
H3: Specifying cacheable templates
> database ldap
> suffix "dc=example,dc=com"
-> uri ldap://ldap.example.com/dc=example,dc=com
+> rootdn "dc=example,dc=com"
+> uri ldap://ldap.example.com/dc=example%2cdc=com
> overlay proxycache
> proxycache bdb 100000 1 1000 100
> proxyAttrset 0 mail postaladdress telephonenumber
> index cn,sn,uid,mail pres,eq,sub
+H4: Cacheable Queries
+
+A LDAP search query is cacheable when its filter matches one of the
+templates as defined in the "proxyTemplate" statements and when it references
+only the attributes specified in the corresponding attribute set.
+In the example above the attribute set number 0 defines that only the
+attributes: {{EX:mail postaladdress telephonenumber}} are cached for the following
+proxyTemplates.
+
+H4: Examples:
+
+> Filter: (&(sn=Richard*)(givenName=jack))
+> Attrs: mail telephoneNumber
+
+ is cacheable, because it matches the template {{EX:(&(sn=)(givenName=))}} and its
+ attributes are contained in proxyAttrset 0.
+
+> Filter: (&(sn=Richard*)(telephoneNumber))
+> Attrs: givenName
+
+ is not cacheable, because the filter does not match the template,
+ nor is the attribute givenName stored in the cache
+
+> Filter: (|(sn=Richard*)(givenName=jack))
+> Attrs: mail telephoneNumber
+
+ is not cacheable, because the filter does not match the template ( logical
+ OR "|" condition instead of logical AND "&" )
+
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