1 .TH SLAPO-PCACHE 5 "RELEASEDATE" "OpenLDAP LDVERSION"
2 .\" Copyright 1998-2006 The OpenLDAP Foundation, All Rights Reserved.
3 .\" Copying restrictions apply. See the COPYRIGHT file.
4 .\" Copyright 2001, Pierangelo Masarati, All rights reserved. <ando@sys-net.it>
7 slapo-pcache \- proxycache overlay
15 allows caching of LDAP search requests (queries) in a local database.
16 For an incoming query, the
17 proxy cache determines its corresponding \fBtemplate\fP. If the template
18 was specified as cacheable using the \fBproxytemplate\fP directive
19 and the request is contained in a cached request, it is answered from
21 Otherwise, the search is performed as usual and cacheable search results
22 are saved in the cache for use in future queries.
25 A template is defined by a filter string and an index identifying a set of
26 attributes. The \fBtemplate string\fP for a query can be obtained by
27 removing assertion values from the RFC 2254 representation of its search
28 filter. A query belongs to a template if its template string and set of
29 projected attributes correspond to a cacheable template.
30 Examples of template strings are \fB(mail=)\fP, \fB(|(sn=)(cn=))\fP,
31 \fB(&(sn=)(givenName=))\fP.
34 The config directives that are specific to the
36 overlay can be prefixed by
38 to avoid conflicts with directives specific to the underlying database
39 or to other stacked overlays. This may be particularly useful for those
40 directives that refer to the backend used for local storage.
41 The following cache specific directives can be used to configure the proxy
45 This directive adds the proxy cache overlay to the current backend. The
46 proxy cache overlay may be used with any backend but is intended for use
54 .B proxycache <database> <max_entries> <numattrsets> <entry_limit> <cc_period>
55 The directive enables proxy caching in the current backend and sets general
56 cache parameters. A <database> backend will be used internally to maintain
57 the cached entries. The chosen database will need to be configured as well,
58 as shown below. Cache replacement is invoked when the cache size grows to
59 <max_entries> entries and continues till the cache size drops below this size.
60 <numattrsets> should be equal to the number of following \fBproxyattrset\fP
61 directives. Queries are cached only if they correspond to a cacheable template
62 (specified by the \fBproxytemplate\fP directive) and the number of entries
63 returned is less than <entry_limit>. Consistency check is performed every
64 <cc_period> duration (specified in secs). In each cycle queries with expired
65 "time to live(\fBTTL\fP)" are removed. A sample cache configuration is:
68 proxycache \fBbdb 10000 1 50 100\fP
71 .B proxyattrset <index> <attrs...>
72 Used to associate a set of attributes <attrs..> with an <index>. Each attribute
73 set is associated with an integer from 0 to <numattrsets>-1. These indices are
74 used by the \fBproxytemplate\fP directive to define cacheable templates.
77 .B proxytemplate <template_string> <attrset_index> <ttl>
78 Specifies a cacheable template and "time to live" (in sec) <ttl> of queries
79 belonging to the template.
82 .B response-callback { head | tail }
83 Specifies whether the response callback should be placed at the
85 (the default) or at the
87 (actually, wherever the stacking sequence would make it appear)
88 of the callback list. This affects how the overlay interacts with other
89 overlays, since the proxycache overlay should be executed as early
90 as possible (and thus configured as late as possible), to get
91 a chance to return the cached results; however, if executed early
92 at response, it would cache entries that may be later "massaged"
93 by other databases and thus returned \fIafter\fP massaging the first
94 time, and \fIbefore\fP massaging when cached.
97 There are some constraints:
99 all values must be positive;
102 must be less than or equal to
106 attribute sets SHOULD be defined by using the directive
109 all attribute sets SHOULD be referenced by (at least) one
114 The following adds a template with filter string \fB((&sn=)(givenName=))\fP
115 and attributes mail, postaladdress, telephonenumber and a TTL of 1 hour.
119 proxyattrset \fB0 mail postaladdress telephonenumber\fP
120 proxytemplate \fB(&(sn=)(givenName=)) 0 3600\fP
125 Directives for configuring the underlying database must also be given, as
130 directory /var/tmp/cache
135 Any valid directives for the chosen database type may be used.
137 Caching data is prone to inconsistencies because updates on the remote server
138 will not be reflected in the response of the cache at least (and at most)
139 for the duration of the
143 The remote server should expose the
145 attribute because the underlying database that actually caches the entries
146 may need it for optimal local processing of the queries.
148 Another potential (and subtle) inconsistency may occur when data is retrieved
149 with different identities and specific per-identity access control
150 is enforced by the remote server.
151 If data was retrieved with an identity that collected only partial results
152 because of access rules enforcement on the remote server, other users
153 with different access privileges on the remote server will get different
154 results from the remote server and from the cache.
155 If those users have higher access privileges on the remote server, they will
156 get from the cache only a subset of the results they would get directly
157 from the remote server; but if they have lower access privileges, they will
158 get from the cache a superset of the results they would get directly
159 from the remote server.
160 Either occurrence may or may not be acceptable, based on the security policy
161 of the cache and of the remote server.
162 It is important to note that in this case the proxy is violating the security
163 of the remote server by disclosing to an identity data that was collected
165 For this reason, it is suggested that, when using
167 proxy caching be used in conjunction with the
168 .I identity assertion
175 statements), so that remote server interrogation occurs with a vanilla identity
176 that has some relatively high
180 access privileges, and the "real" access control is delegated to the proxy's ACLs.
181 Beware that since only the cached fraction of the real datum is available
182 to the cache, it may not be possible to enforce the same access rules that
183 are defined on the remote server.
184 When security is a concern, cached proxy access must be carefully tailored.
189 default slapd configuration file
197 Originally implemented by Apurva Kumar as an extension to back-meta;
198 turned into an overlay by Howard Chu.