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