|
NAME | SYNOPSIS | DESCRIPTION | BACKWARD COMPATIBILITY | CAVEATS | FILES | SEE ALSO | AUTHOR | COLOPHON |
SLAPO-PCACHE(5) File Formats Manual SLAPO-PCACHE(5)
slapo-pcache - proxy cache overlay to slapd
ETCDIR/slapd.conf
The pcache overlay to slapd(8) allows caching of LDAP search requests
(queries) in a local database. For an incoming query, the proxy
cache determines its corresponding template. If the template was
specified as cacheable using the pcacheTemplate directive and the
request is contained in a cached request, it is answered from the
proxy cache. Otherwise, the search is performed as usual and
cacheable search results are saved in the cache for use in future
queries.
A template is defined by a filter string and an index identifying a
set of attributes. The template string for a query can be obtained by
removing assertion values from the RFC 4515 representation of its
search filter. A query belongs to a template if its template string
and set of projected attributes correspond to a cacheable template.
Examples of template strings are (mail=), (|(sn=)(cn=)),
(&(sn=)(givenName=)).
The config directives that are specific to the pcache overlay can be
prefixed by pcache-, to avoid conflicts with directives specific to
the underlying database or to other stacked overlays. This may be
particularly useful for those directives that refer to the backend
used for local storage. The following cache specific directives can
be used to configure the proxy cache:
overlay pcache
This directive adds the proxy cache overlay to the current
backend. The proxy cache overlay may be used with any backend
but is intended for use with the ldap, meta, and sql backends.
Please note that the underlying backend must have a configured
rootdn.
pcache <database> <max_entries> <numattrsets> <entry_limit>
<cc_period>
The directive enables proxy caching in the current backend and
sets general cache parameters. A <database> backend will be
used internally to maintain the cached entries. The chosen
database will need to be configured as well, as shown below.
Cache replacement is invoked when the cache size grows to
<max_entries> entries and continues till the cache size drops
below this size. <numattrsets> should be equal to the number
of following pcacheAttrset directives. Queries are cached only
if they correspond to a cacheable template (specified by the
pcacheTemplate directive) and the number of entries returned
is less than <entry_limit>. Consistency check is performed
every <cc_period> duration (specified in secs). In each cycle
queries with expired "time to live(TTL)" are removed. A sample
cache configuration is:
pcache mdb 10000 1 50 100
pcacheAttrset <index> <attrs...>
Used to associate a set of attributes <attrs..> with an
<index>. Each attribute set is associated with an integer from
0 to <numattrsets>-1. These indices are used by the
pcacheTemplate directive to define cacheable templates. A set
of attributes cannot be empty. A set of attributes can
contain the special attributes "*" (all user attributes), "+"
(all operational attributes) or both; in the latter case, any
other attribute is redundant and should be avoided for
clarity. A set of attributes can contain "1.1" as the only
attribute; in this case, only the presence of the entries is
cached. Attributes prefixed by "undef:" need not be present
in the schema.
pcacheMaxQueries <queries>
Specify the maximum number of queries to cache. The default is
10000.
pcacheValidate { TRUE | FALSE }
Check whether the results of a query being cached can actually
be returned from the cache by the proxy DSA. When enabled,
the entries being returned while caching the results of a
query are checked to ensure consistency with the schema known
to the proxy DSA. In case of failure, the query is not
cached. By default, the check is off.
pcacheOffline { TRUE | FALSE }
Set the cache to offline mode. While offline, the consistency
checker will be stopped and no expirations will occur. This
allows the cache contents to be used indefinitely while the
proxy is cut off from network access to the remote DSA. The
default is FALSE, i.e. consistency checks and expirations will
be performed.
pcachePersist { TRUE | FALSE }
Specify whether the cached queries should be saved across
restarts of the caching proxy, to provide hot startup of the
cache. Only non-expired queries are reloaded. The default is
FALSE.
CAVEAT: of course, the configuration of the proxy cache must
not change across restarts; the pcache overlay does not
perform any consistency checks in this sense. In detail, this
option should be disabled unless the existing pcacheAttrset
and pcacheTemplate directives are not changed neither in order
nor in contents. If new sets and templates are added, or if
other details of the pcache overlay configuration changed,
this feature should not be affected.
pcacheTemplate <template_string> <attrset_index> <ttl> [<negttl>
[<limitttl> [<ttr>]]]
Specifies a cacheable template and "time to live" <ttl> of
queries belonging to the template. An optional <negttl> can be
used to specify that negative results (i.e., queries that
returned zero entries) should also be cached for the specified
amount of time. Negative results are not cached by default
(<negttl> set to 0). An optional <limitttl> can be used to
specify that results hitting a sizelimit should also be cached
for the specified amount of time. Results hitting a sizelimit
are not cached by default (<limitttl> set to 0). An optional
<ttr> "time to refresh" can be used to specify that cached
entries should be automatically refreshed after a certain
time. Entries will only be refreshed while they have not
expired, so the <ttl> should be larger than the <ttr> for this
option to be useful. Entries are not refreshed by default
(<ttr> set to 0).
pcacheBind <filter_template> <attrset_index> <ttr> <scope> <base>
Specifies a template for caching Simple Bind credentials based
on an already defined pcacheTemplate. The <filter_template> is
similar to a <template_string> except that it may have some
values present. Its purpose is to allow the overlay to
generate filters similar to what other applications do when
they do a Search immediately before a Bind. E.g., if a client
like nss_ldap is configured to search for a user with the
filter "(&(objectClass=posixAccount)(uid=<username>))" then
the corresponding template
"(&(objectClass=posixAccount)(uid=))" should be used here.
When converted to a regular template e.g.
"(&(objectClass=)(uid=))" this template and the
<attrset_index> must match an already defined pcacheTemplate
clause. The "time to refresh" <ttr> determines the time
interval after which the cached credentials may be refreshed.
The first Bind request that occurs after that time will
trigger the refresh attempt. Refreshes are not performed when
the overlay is Offline. There is no "time to live" parameter
for the Bind credentials; the credentials will expire
according to the pcacheTemplate ttl. The <scope> and <base>
should match the search scope and base used by the
authentication clients. The cached credentials are not stored
in cleartext, they are hashed using the default password hash.
By default Bind caching is not enabled.
pcachePosition { head | tail }
Specifies whether the response callback should be placed at
the tail (the default) or at the head (actually, wherever the
stacking sequence would make it appear) of the callback list.
This affects how the overlay interacts with other overlays,
since the proxycache overlay should be executed as early as
possible (and thus configured as late as possible), to get a
chance to return the cached results; however, if executed
early at response, it would cache entries that may be later
"massaged" by other databases and thus returned after
massaging the first time, and before massaging when cached.
There are some constraints:
all values must be positive;
<entry_limit> must be less than or equal to <max_entries>;
<numattrsets> attribute sets SHOULD be defined by using the
directive pcacheAttrset;
all attribute sets SHOULD be referenced by (at least) one
pcacheTemplate directive;
The following adds a template with filter string (&(sn=)(givenName=))
and attributes mail, postaladdress, telephonenumber and a TTL of 1
hour.
pcacheAttrset 0 mail postaladdress telephonenumber
pcacheTemplate (&(sn=)(givenName=)) 0 3600
Directives for configuring the underlying database must also be
given, as shown here:
directory /var/tmp/cache
cachesize 100
Any valid directives for the chosen database type may be used.
Indexing should be used as appropriate for the queries being handled.
In addition, an equality index on the pcacheQueryid attribute should
be configured, to assist in the removal of expired query data.
The configuration keywords have been renamed and the older form is
deprecated. These older keywords are still recognized but may
disappear in future releases.
proxycache
use pcache
proxyattrset
use pcacheAttrset
proxycachequeries
use pcacheMaxQueries
proxycheckcacheability
use pcacheValidate
proxysavequeries
use pcachePersist
proxytemplate
use pcacheTemplate
response-callback
use pcachePosition
Caching data is prone to inconsistencies because updates on the
remote server will not be reflected in the response of the cache at
least (and at most) for the duration of the pcacheTemplate TTL.
These inconsistencies can be minimized by careful use of the TTR.
The remote server should expose the objectClass attribute because the
underlying database that actually caches the entries may need it for
optimal local processing of the queries.
The proxy server should contain all the schema information required
for caching. Significantly, it needs the schema of attributes used
in the query templates. If the objectClass attribute is used in a
query template, it needs the definition of the objectClasses of the
entries it is supposed to cache. It is the responsibility of the
proxy administrator to keep the proxy schema lined up with that of
the proxied server.
Another potential (and subtle) inconsistency may occur when data is
retrieved with different identities and specific per-identity access
control is enforced by the remote server. If data was retrieved with
an identity that collected only partial results because of access
rules enforcement on the remote server, other users with different
access privileges on the remote server will get different results
from the remote server and from the cache. If those users have
higher access privileges on the remote server, they will get from the
cache only a subset of the results they would get directly from the
remote server; but if they have lower access privileges, they will
get from the cache a superset of the results they would get directly
from the remote server. Either occurrence may or may not be
acceptable, based on the security policy of the cache and of the
remote server. It is important to note that in this case the proxy
is violating the security of the remote server by disclosing to an
identity data that was collected by another identity. For this
reason, it is suggested that, when using back-ldap, proxy caching be
used in conjunction with the identity assertion feature of
slapd-ldap(5) (see the idassert-bind and the idassert-authz
statements), so that remote server interrogation occurs with a
vanilla identity that has some relatively high search and read access
privileges, and the "real" access control is delegated to the proxy's
ACLs. Beware that since only the cached fraction of the real datum
is available to the cache, it may not be possible to enforce the same
access rules that are defined on the remote server. When security is
a concern, cached proxy access must be carefully tailored.
ETCDIR/slapd.conf
default slapd configuration file
slapd.conf(5), slapd-config(5), slapd-ldap(5), slapd-meta(5),
slapd-sql(5), slapd(8).
Originally implemented by Apurva Kumar as an extension to back-meta;
turned into an overlay by Howard Chu.
This page is part of the OpenLDAP (an open source implementation of
the Lightweight Directory Access Protocol) project. Information
about the project can be found at ⟨http://www.openldap.org/⟩. If you
have a bug report for this manual page, see
⟨http://www.openldap.org/its/⟩. This page was obtained from the
project's upstream Git repository
⟨git://git.openldap.org/openldap.git⟩ on 2017-07-05. If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page, or
you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
OpenLDAP LDVERSION RELEASEDATE SLAPO-PCACHE(5)
Pages that refer to this page: slapd-asyncmeta(5), slapd-ldap(5), slapd-meta(5), slapd.overlays(5), slapd-sql(5)