1 .TH SLAPO-PCACHE 5 "RELEASEDATE" "OpenLDAP LDVERSION"
2 .\" Copyright 1998-2009 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 \- proxy cache 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 \fBpcacheTemplate\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 pcache <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 \fBpcacheAttrset\fP
61 directives. Queries are cached only if they correspond to a cacheable template
62 (specified by the \fBpcacheTemplate\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 pcache \fBbdb 10000 1 50 100\fP
72 .B pcacheAttrset <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 \fBpcacheTemplate\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 pcacheMaxQueries <queries>
84 Specify the maximum number of queries to cache. The default is 10000.
87 .B pcacheValidate { 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 pcacheOffline { TRUE | FALSE }
96 Set the cache to offline mode. While offline, the consistency checker
97 will be stopped and no expirations will occur. This allows the cache
98 contents to be used indefinitely while the proxy is cut off from network
99 access to the remote DSA. The default is FALSE, i.e. consistency
100 checks and expirations will be performed.
103 .B pcachePersist { TRUE | FALSE }
104 Specify whether the cached queries should be saved across restarts
105 of the caching proxy, to provide hot startup of the cache. Only non-expired
106 queries are reloaded. The default is FALSE.
109 of course, the configuration of the proxy cache must not change
110 across restarts; the pcache overlay does not perform any consistency
111 checks in this sense.
112 In detail, this option should be disabled unless the existing
116 directives are not changed neither in order nor in contents.
117 If new sets and templates are added, or if other details of the pcache
118 overlay configuration changed, this feature should not be affected.
121 .B pcacheTemplate <template_string> <attrset_index> <ttl> [<negttl> [<limitttl> [<ttr>]]]
122 Specifies a cacheable template and "time to live" <ttl> of queries
123 belonging to the template. An optional <negttl> can be used to specify
124 that negative results (i.e., queries that returned zero entries)
125 should also be cached for the specified amount of time. Negative
126 results are not cached by default (<negttl> set to 0).
127 An optional <limitttl> can be used to specify that results
128 hitting a sizelimit should also be cached for the specified amount of time.
129 Results hitting a sizelimit are not cached by default (<limitttl> set to 0).
130 An optional <ttr> "time to refresh" can be used to specify that cached
131 entries should be automatically refreshed after a certain time. Entries
132 will only be refreshed while they have not expired, so the <ttl> should
133 be larger than the <ttr> for this option to be useful. Entries are not
134 refreshed by default (<ttr> set to 0).
137 .B pcachePosition { head | tail }
138 Specifies whether the response callback should be placed at the
140 (the default) or at the
142 (actually, wherever the stacking sequence would make it appear)
143 of the callback list. This affects how the overlay interacts with other
144 overlays, since the proxycache overlay should be executed as early
145 as possible (and thus configured as late as possible), to get
146 a chance to return the cached results; however, if executed early
147 at response, it would cache entries that may be later "massaged"
148 by other databases and thus returned \fIafter\fP massaging the first
149 time, and \fIbefore\fP massaging when cached.
152 There are some constraints:
154 all values must be positive;
157 must be less than or equal to
161 attribute sets SHOULD be defined by using the directive
164 all attribute sets SHOULD be referenced by (at least) one
169 The following adds a template with filter string \fB(&(sn=)(givenName=))\fP
170 and attributes mail, postaladdress, telephonenumber and a TTL of 1 hour.
174 pcacheAttrset \fB0 mail postaladdress telephonenumber\fP
175 pcacheTemplate \fB(&(sn=)(givenName=)) 0 3600\fP
180 Directives for configuring the underlying database must also be given, as
185 directory /var/tmp/cache
190 Any valid directives for the chosen database type may be used. Indexing
191 should be used as appropriate for the queries being handled. In addition,
192 an equality index on the \fBqueryid\fP attribute should be configured, to
193 assist in the removal of expired query data.
194 .SH BACKWARD COMPATIBILITY
195 The configuration keywords have been renamed and the older form is
196 deprecated. These older keywords are still recognized but may disappear
212 .B proxycheckcacheability
228 Caching data is prone to inconsistencies because updates on the remote server
229 will not be reflected in the response of the cache at least (and at most)
230 for the duration of the
233 These inconsistencies can be minimized by careful use of the TTR.
235 The remote server should expose the
237 attribute because the underlying database that actually caches the entries
238 may need it for optimal local processing of the queries.
240 The proxy server should contain all the schema information required for caching.
241 Significantly, it needs the schema of attributes used in the query templates.
242 If the objectClass attribute is used in a query template, it needs the definition
243 of the objectClasses of the entries it is supposed to cache.
244 It is the responsibility of the proxy administrator to keep the proxy schema
245 lined up with that of the proxied server.
247 Another potential (and subtle) inconsistency may occur when data is retrieved
248 with different identities and specific per-identity access control
249 is enforced by the remote server.
250 If data was retrieved with an identity that collected only partial results
251 because of access rules enforcement on the remote server, other users
252 with different access privileges on the remote server will get different
253 results from the remote server and from the cache.
254 If those users have higher access privileges on the remote server, they will
255 get from the cache only a subset of the results they would get directly
256 from the remote server; but if they have lower access privileges, they will
257 get from the cache a superset of the results they would get directly
258 from the remote server.
259 Either occurrence may or may not be acceptable, based on the security policy
260 of the cache and of the remote server.
261 It is important to note that in this case the proxy is violating the security
262 of the remote server by disclosing to an identity data that was collected
264 For this reason, it is suggested that, when using
266 proxy caching be used in conjunction with the
267 .I identity assertion
274 statements), so that remote server interrogation occurs with a vanilla identity
275 that has some relatively high
279 access privileges, and the "real" access control is delegated to the proxy's ACLs.
280 Beware that since only the cached fraction of the real datum is available
281 to the cache, it may not be possible to enforce the same access rules that
282 are defined on the remote server.
283 When security is a concern, cached proxy access must be carefully tailored.
288 default slapd configuration file
291 .BR slapd\-config (5),
297 Originally implemented by Apurva Kumar as an extension to back-meta;
298 turned into an overlay by Howard Chu.
projects / openldap / blob