1 .TH SLAPO-PCACHE 5 "RELEASEDATE" "OpenLDAP LDVERSION"
2 .\" Copyright 1998-2007 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 .B proxyattrset <index> <attrs...>
83 Used to associate a set of attributes <attrs..> with an <index>. Each attribute
84 set is associated with an integer from 0 to <numattrsets>-1. These indices are
85 used by the \fBproxytemplate\fP directive to define cacheable templates.
86 A set of attributes cannot be empty. A set of attributes can contain the
87 special attributes "*" (all user attributes), "+" (all operational attributes)
88 or both; in the latter case, any other attribute is redundant and should
89 be avoided for clarity. A set of attributes can contain "1.1" as the only
90 attribute; in this case, only the presence of the entries is cached.
93 .B proxytemplate <template_string> <attrset_index> <ttl> [<negttl>]
94 Specifies a cacheable template and "time to live" (in sec) <ttl> of queries
95 belonging to the template. An optional <negttl> can be used to specify
96 that negative results (i.e., queries that returned zero entries)
97 should also be cached for the specified number of seconds. Negative
98 results are not cached by default.
101 .B response-callback { head | tail }
102 Specifies whether the response callback should be placed at the
104 (the default) or at the
106 (actually, wherever the stacking sequence would make it appear)
107 of the callback list. This affects how the overlay interacts with other
108 overlays, since the proxycache overlay should be executed as early
109 as possible (and thus configured as late as possible), to get
110 a chance to return the cached results; however, if executed early
111 at response, it would cache entries that may be later "massaged"
112 by other databases and thus returned \fIafter\fP massaging the first
113 time, and \fIbefore\fP massaging when cached.
116 There are some constraints:
118 all values must be positive;
121 must be less than or equal to
125 attribute sets SHOULD be defined by using the directive
128 all attribute sets SHOULD be referenced by (at least) one
133 The following adds a template with filter string \fB(&(sn=)(givenName=))\fP
134 and attributes mail, postaladdress, telephonenumber and a TTL of 1 hour.
138 proxyattrset \fB0 mail postaladdress telephonenumber\fP
139 proxytemplate \fB(&(sn=)(givenName=)) 0 3600\fP
144 Directives for configuring the underlying database must also be given, as
149 directory /var/tmp/cache
154 Any valid directives for the chosen database type may be used. Indexing
155 should be used as appropriate for the queries being handled. In addition,
156 an equality index on the \fBqueryid\fP attribute should be configured, to
157 assist in the removal of expired query data.
159 Caching data is prone to inconsistencies because updates on the remote server
160 will not be reflected in the response of the cache at least (and at most)
161 for the duration of the
165 The remote server should expose the
167 attribute because the underlying database that actually caches the entries
168 may need it for optimal local processing of the queries.
170 Another potential (and subtle) inconsistency may occur when data is retrieved
171 with different identities and specific per-identity access control
172 is enforced by the remote server.
173 If data was retrieved with an identity that collected only partial results
174 because of access rules enforcement on the remote server, other users
175 with different access privileges on the remote server will get different
176 results from the remote server and from the cache.
177 If those users have higher access privileges on the remote server, they will
178 get from the cache only a subset of the results they would get directly
179 from the remote server; but if they have lower access privileges, they will
180 get from the cache a superset of the results they would get directly
181 from the remote server.
182 Either occurrence may or may not be acceptable, based on the security policy
183 of the cache and of the remote server.
184 It is important to note that in this case the proxy is violating the security
185 of the remote server by disclosing to an identity data that was collected
187 For this reason, it is suggested that, when using
189 proxy caching be used in conjunction with the
190 .I identity assertion
197 statements), so that remote server interrogation occurs with a vanilla identity
198 that has some relatively high
202 access privileges, and the "real" access control is delegated to the proxy's ACLs.
203 Beware that since only the cached fraction of the real datum is available
204 to the cache, it may not be possible to enforce the same access rules that
205 are defined on the remote server.
206 When security is a concern, cached proxy access must be carefully tailored.
211 default slapd configuration file
219 Originally implemented by Apurva Kumar as an extension to back-meta;
220 turned into an overlay by Howard Chu.
projects / openldap / blob