1SLAPO-PCACHE(5) File Formats Manual SLAPO-PCACHE(5)
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6 slapo-pcache - proxy cache overlay to slapd
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9 /etc/openldap/slapd.conf
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12 The pcache overlay to slapd(8) allows caching of LDAP search requests
13 (queries) in a local database. For an incoming query, the proxy cache
14 determines its corresponding template. If the template was specified as
15 cacheable using the pcacheTemplate directive and the request is con‐
16 tained in a cached request, it is answered from the proxy cache. Oth‐
17 erwise, the search is performed as usual and cacheable search results
18 are saved in the cache for use in future queries.
19 A template is defined by a filter string and an index identifying a set
21 of attributes. The template string for a query can be obtained by
22 removing assertion values from the RFC 4515 representation of its
23 search filter. A query belongs to a template if its template string and
24 set of projected attributes correspond to a cacheable template. Exam‐
25 ples of template strings are (mail=), (|(sn=)(cn=)), (&(sn=)(given‐
26 Name=)).
27 The config directives that are specific to the pcache overlay can be
30 prefixed by pcache-, to avoid conflicts with directives specific to the
31 underlying database or to other stacked overlays. This may be particu‐
32 larly useful for those directives that refer to the backend used for
33 local storage. The following cache specific directives can be used to
34 configure the proxy cache:
35 overlay pcache
37 This directive adds the proxy cache overlay to the current back‐
38 end. The proxy cache overlay may be used with any backend but is
39 intended for use with the ldap, meta, and sql backends.
40 pcache <database> <max_entries> <numattrsets> <entry_limit> <cc_period>
42 The directive enables proxy caching in the current backend and
43 sets general cache parameters. A <database> backend will be used
44 internally to maintain the cached entries. The chosen database
45 will need to be configured as well, as shown below. Cache
46 replacement is invoked when the cache size grows to
47 <max_entries> entries and continues till the cache size drops
48 below this size. <numattrsets> should be equal to the number of
49 following pcacheAttrset directives. Queries are cached only if
50 they correspond to a cacheable template (specified by the pca‐
51 cheTemplate directive) and the number of entries returned is
52 less than <entry_limit>. Consistency check is performed every
53 <cc_period> duration (specified in secs). In each cycle queries
54 with expired "time to live(TTL)" are removed. A sample cache
55 configuration is:
56 pcache bdb 10000 1 50 100
58 pcacheAttrset <index> <attrs...>
61 Used to associate a set of attributes <attrs..> with an <index>.
62 Each attribute set is associated with an integer from 0 to
63 <numattrsets>-1. These indices are used by the pcacheTemplate
64 directive to define cacheable templates. A set of attributes
65 cannot be empty. A set of attributes can contain the special
66 attributes "*" (all user attributes), "+" (all operational
67 attributes) or both; in the latter case, any other attribute is
68 redundant and should be avoided for clarity. A set of
69 attributes can contain "1.1" as the only attribute; in this
70 case, only the presence of the entries is cached.
71 pcacheMaxQueries <queries>
74 Specify the maximum number of queries to cache. The default is
75 10000.
76 pcacheValidate { TRUE | FALSE }
79 Check whether the results of a query being cached can actually
80 be returned from the cache by the proxy DSA. When enabled, the
81 entries being returned while caching the results of a query are
82 checked to ensure consistency with the schema known to the proxy
83 DSA. In case of failure, the query is not cached. By default,
84 the check is off.
85 pcacheOffline { TRUE | FALSE }
88 Set the cache to offline mode. While offline, the consistency
89 checker will be stopped and no expirations will occur. This
90 allows the cache contents to be used indefinitely while the
91 proxy is cut off from network access to the remote DSA. The
92 default is FALSE, i.e. consistency checks and expirations will
93 be performed.
94 pcachePersist { TRUE | FALSE }
97 Specify whether the cached queries should be saved across
98 restarts of the caching proxy, to provide hot startup of the
99 cache. Only non-expired queries are reloaded. The default is
100 FALSE.
101 CAVEAT: of course, the configuration of the proxy cache must not
103 change across restarts; the pcache overlay does not perform any
104 consistency checks in this sense. In detail, this option should
105 be disabled unless the existing pcacheAttrset and pcacheTemplate
106 directives are not changed neither in order nor in contents. If
107 new sets and templates are added, or if other details of the
108 pcache overlay configuration changed, this feature should not be
109 affected.
110 pcacheTemplate <template_string> <attrset_index> <ttl> [<negttl>
113 [<limitttl> [<ttr>]]]
114 Specifies a cacheable template and "time to live" <ttl> of
115 queries belonging to the template. An optional <negttl> can be
116 used to specify that negative results (i.e., queries that
117 returned zero entries) should also be cached for the specified
118 amount of time. Negative results are not cached by default
119 (<negttl> set to 0). An optional <limitttl> can be used to
120 specify that results hitting a sizelimit should also be cached
121 for the specified amount of time. Results hitting a sizelimit
122 are not cached by default (<limitttl> set to 0). An optional
123 <ttr> "time to refresh" can be used to specify that cached
124 entries should be automatically refreshed after a certain time.
125 Entries will only be refreshed while they have not expired, so
126 the <ttl> should be larger than the <ttr> for this option to be
127 useful. Entries are not refreshed by default (<ttr> set to 0).
128 pcacheBind <filter_template> <attrset_index> <ttr> <scope> <base>
131 Specifies a template for caching Simple Bind credentials based
132 on an already defined pcacheTemplate. The <filter_template> is
133 similar to a <template_string> except that it may have some val‐
134 ues present. Its purpose is to allow the overlay to generate
135 filters similar to what other applications do when they do a
136 Search immediately before a Bind. E.g., if a client like
137 nss_ldap is configured to search for a user with the filter
138 "(&(objectClass=posixAccount)(uid=<username>))" then the corre‐
139 sponding template "(&(objectClass=posixAccount)(uid=))" should
140 be used here. When converted to a regular template e.g.
141 "(&(objectClass=)(uid=))" this template and the <attrset_index>
142 must match an already defined pcacheTemplate clause. The "time
143 to refresh" <ttr> determines the time interval after which the
144 cached credentials may be refreshed. The first Bind request that
145 occurs after that time will trigger the refresh attempt.
146 Refreshes are not performed when the overlay is Offline. There
147 is no "time to live" parameter for the Bind credentials; the
148 credentials will expire according to the pcacheTemplate ttl. The
149 <scope> and <base> should match the search scope and base used
150 by the authentication clients. The cached credentials are not
151 stored in cleartext, they are hashed using the default password
152 hash. By default Bind caching is not enabled.
153 pcachePosition { head | tail }
156 Specifies whether the response callback should be placed at the
157 tail (the default) or at the head (actually, wherever the stack‐
158 ing sequence would make it appear) of the callback list. This
159 affects how the overlay interacts with other overlays, since the
160 proxycache overlay should be executed as early as possible (and
161 thus configured as late as possible), to get a chance to return
162 the cached results; however, if executed early at response, it
163 would cache entries that may be later "massaged" by other data‐
164 bases and thus returned after massaging the first time, and
165 before massaging when cached.
166 There are some constraints:
169 all values must be positive;
171 <entry_limit> must be less than or equal to <max_entries>;
173 <numattrsets> attribute sets SHOULD be defined by using the
175 directive pcacheAttrset;
176 all attribute sets SHOULD be referenced by (at least) one pca‐
178 cheTemplate directive;
179 The following adds a template with filter string (&(sn=)(givenName=))
182 and attributes mail, postaladdress, telephonenumber and a TTL of 1
183 hour.
184 pcacheAttrset 0 mail postaladdress telephonenumber
186 pcacheTemplate (&(sn=)(givenName=)) 0 3600
187 Directives for configuring the underlying database must also be given,
190 as shown here:
191 directory /var/tmp/cache
193 cachesize 100
194 Any valid directives for the chosen database type may be used. Indexing
196 should be used as appropriate for the queries being handled. In addi‐
197 tion, an equality index on the pcacheQueryid attribute should be con‐
198 figured, to assist in the removal of expired query data.
199
201 The configuration keywords have been renamed and the older form is dep‐
202 recated. These older keywords are still recognized but may disappear in
203 future releases.
204 proxycache
207 use pcache
208 proxyattrset
211 use pcacheAttrset
212 proxycachequeries
215 use pcacheMaxQueries
216 proxycheckcacheability
219 use pcacheValidate
220 proxysavequeries
223 use pcachePersist
224 proxytemplate
227 use pcacheTemplate
228 response-callback
231 use pcachePosition
232
235 Caching data is prone to inconsistencies because updates on the remote
236 server will not be reflected in the response of the cache at least (and
237 at most) for the duration of the pcacheTemplate TTL. These inconsis‐
238 tencies can be minimized by careful use of the TTR.
239 The remote server should expose the objectClass attribute because the
241 underlying database that actually caches the entries may need it for
242 optimal local processing of the queries.
243 The proxy server should contain all the schema information required for
245 caching. Significantly, it needs the schema of attributes used in the
246 query templates. If the objectClass attribute is used in a query tem‐
247 plate, it needs the definition of the objectClasses of the entries it
248 is supposed to cache. It is the responsibility of the proxy adminis‐
249 trator to keep the proxy schema lined up with that of the proxied
250 server.
251 Another potential (and subtle) inconsistency may occur when data is
253 retrieved with different identities and specific per-identity access
254 control is enforced by the remote server. If data was retrieved with
255 an identity that collected only partial results because of access rules
256 enforcement on the remote server, other users with different access
257 privileges on the remote server will get different results from the
258 remote server and from the cache. If those users have higher access
259 privileges on the remote server, they will get from the cache only a
260 subset of the results they would get directly from the remote server;
261 but if they have lower access privileges, they will get from the cache
262 a superset of the results they would get directly from the remote
263 server. Either occurrence may or may not be acceptable, based on the
264 security policy of the cache and of the remote server. It is important
265 to note that in this case the proxy is violating the security of the
266 remote server by disclosing to an identity data that was collected by
267 another identity. For this reason, it is suggested that, when using
268 back-ldap, proxy caching be used in conjunction with the identity
269 assertion feature of slapd-ldap(5) (see the idassert-bind and the
270 idassert-authz statements), so that remote server interrogation occurs
271 with a vanilla identity that has some relatively high search and read
272 access privileges, and the "real" access control is delegated to the
273 proxy's ACLs. Beware that since only the cached fraction of the real
274 datum is available to the cache, it may not be possible to enforce the
275 same access rules that are defined on the remote server. When security
276 is a concern, cached proxy access must be carefully tailored.
277
279 /etc/openldap/slapd.conf
280 default slapd configuration file
281
283 slapd.conf(5), slapd-config(5), slapd-ldap(5), slapd-meta(5),
284 slapd-sql(5), slapd(8).
285
287 Originally implemented by Apurva Kumar as an extension to back-meta;
288 turned into an overlay by Howard Chu.
289OpenLDAP 2.4.23 2010/06/30 SLAPO-PCACHE(5)