1 .TH SLAPO-PCACHE 5 "RELEASEDATE" "OpenLDAP LDVERSION"
2 .\" Copyright 1998-2008 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 to slapd
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 4515 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
72 .B proxycachequeries <queries>
73 Specify the maximum number of queries to cache. The default is 10000.
76 .B proxysavequeries { TRUE | FALSE }
77 Specify whether the cached queries should be saved across restarts
78 of the caching proxy, to provide hot startup of the cache. Only non-expired
79 queries are reloaded. The default is FALSE.
82 of course, the configuration of the proxycache must not change
83 across restarts; the pcache overlay does not perform any consistency
85 In detail, this option should be disabled unless the existing
89 directives are not changed neither in order nor in contents.
90 If new sets and templates are added, or if other details of the pcache
91 overlay configuration changed, this feature should not be affected.
94 .B proxyattrset <index> <attrs...>
95 Used to associate a set of attributes <attrs..> with an <index>. Each attribute
96 set is associated with an integer from 0 to <numattrsets>-1. These indices are
97 used by the \fBproxytemplate\fP directive to define cacheable templates.
98 A set of attributes cannot be empty. A set of attributes can contain the
99 special attributes "*" (all user attributes), "+" (all operational attributes)
100 or both; in the latter case, any other attribute is redundant and should
101 be avoided for clarity. A set of attributes can contain "1.1" as the only
102 attribute; in this case, only the presence of the entries is cached.
105 .B proxytemplate <template_string> <attrset_index> <ttl> [<negttl> [<limitttl>]]
106 Specifies a cacheable template and "time to live" <ttl> of queries
107 belonging to the template. An optional <negttl> can be used to specify
108 that negative results (i.e., queries that returned zero entries)
109 should also be cached for the specified amount of time. Negative
110 results are not cached by default (<negttl> set to 0).
111 An optional <limitttl> can be used to specify that results
112 hitting a sizelimit should also be cached for the specified amount of time.
113 Results hitting a sizelimit are not cached by default (<limitttl> set to 0).
116 .B response-callback { head | tail }
117 Specifies whether the response callback should be placed at the
119 (the default) or at the
121 (actually, wherever the stacking sequence would make it appear)
122 of the callback list. This affects how the overlay interacts with other
123 overlays, since the proxycache overlay should be executed as early
124 as possible (and thus configured as late as possible), to get
125 a chance to return the cached results; however, if executed early
126 at response, it would cache entries that may be later "massaged"
127 by other databases and thus returned \fIafter\fP massaging the first
128 time, and \fIbefore\fP massaging when cached.
131 There are some constraints:
133 all values must be positive;
136 must be less than or equal to
140 attribute sets SHOULD be defined by using the directive
143 all attribute sets SHOULD be referenced by (at least) one
148 The following adds a template with filter string \fB(&(sn=)(givenName=))\fP
149 and attributes mail, postaladdress, telephonenumber and a TTL of 1 hour.
153 proxyattrset \fB0 mail postaladdress telephonenumber\fP
154 proxytemplate \fB(&(sn=)(givenName=)) 0 3600\fP
159 Directives for configuring the underlying database must also be given, as
164 directory /var/tmp/cache
169 Any valid directives for the chosen database type may be used. Indexing
170 should be used as appropriate for the queries being handled. In addition,
171 an equality index on the \fBqueryid\fP attribute should be configured, to
172 assist in the removal of expired query data.
174 Caching data is prone to inconsistencies because updates on the remote server
175 will not be reflected in the response of the cache at least (and at most)
176 for the duration of the
180 The remote server should expose the
182 attribute because the underlying database that actually caches the entries
183 may need it for optimal local processing of the queries.
185 The proxy server should contain all the schema information required for caching.
186 Significantly, it needs the schema of attributes used in the query templates.
187 If the objectClass attribute is used in a query template, it needs the definition
188 of the objectClasses of the entries it is supposed to cache.
189 It is the responsibility of the proxy administrator to keep the proxy schema
190 lined up with that of the proxied server.
192 Another potential (and subtle) inconsistency may occur when data is retrieved
193 with different identities and specific per-identity access control
194 is enforced by the remote server.
195 If data was retrieved with an identity that collected only partial results
196 because of access rules enforcement on the remote server, other users
197 with different access privileges on the remote server will get different
198 results from the remote server and from the cache.
199 If those users have higher access privileges on the remote server, they will
200 get from the cache only a subset of the results they would get directly
201 from the remote server; but if they have lower access privileges, they will
202 get from the cache a superset of the results they would get directly
203 from the remote server.
204 Either occurrence may or may not be acceptable, based on the security policy
205 of the cache and of the remote server.
206 It is important to note that in this case the proxy is violating the security
207 of the remote server by disclosing to an identity data that was collected
209 For this reason, it is suggested that, when using
211 proxy caching be used in conjunction with the
212 .I identity assertion
219 statements), so that remote server interrogation occurs with a vanilla identity
220 that has some relatively high
224 access privileges, and the "real" access control is delegated to the proxy's ACLs.
225 Beware that since only the cached fraction of the real datum is available
226 to the cache, it may not be possible to enforce the same access rules that
227 are defined on the remote server.
228 When security is a concern, cached proxy access must be carefully tailored.
233 default slapd configuration file
241 Originally implemented by Apurva Kumar as an extension to back-meta;
242 turned into an overlay by Howard Chu.
projects / openldap / blob