.TH SLAPO-PCACHE 5 "RELEASEDATE" "OpenLDAP LDVERSION"
.\" Copyright 1998-2005 The OpenLDAP Foundation, All Rights Reserved.
.\" Copying restrictions apply.  See the COPYRIGHT file.
.\" Copyright 2001, Pierangelo Masarati, All rights reserved. <ando@sys-net.it>
.\" $OpenLDAP$
.SH NAME
slapo-pcache \- proxycache overlay
.SH SYNOPSIS
ETCDIR/slapd.conf
.SH DESCRIPTION
The
.B pcache
overlay to
.BR slapd (8)
allows caching of LDAP search requests (queries) in a local database.
For an incoming query, the
proxy cache determines its corresponding \fBtemplate\fP. If the template
was specified as cacheable using the \fBproxytemplate\fP 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.
.LP

A template is defined by a filter string and an index identifying a set of
attributes. The \fBtemplate string\fP for a query can be obtained by
removing assertion values from the RFC 2254 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 \fB(mail=)\fP, \fB(|(sn=)(cn=))\fP,
\fB(&(sn=)(givenName=))\fP.

.LP 
The config directives that are specific to the
.B proxycache
overlay can be prefixed by
.BR proxycache\- ,
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: 
.TP
.B 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
.BR ldap ,
.BR meta ,
and
.BR sql
backends.
.TP
.B proxycache <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 \fBproxyattrset\fP
directives. Queries are cached only if they correspond to a cacheable template
(specified by the \fBproxytemplate\fP 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(\fBTTL\fP)" are removed. A sample cache configuration is: 
.LP
.RS
proxycache \fBbdb 10000 1 50 100\fP
.RE
.TP
.B proxyattrset <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 \fBproxytemplate\fP directive to define cacheable templates. 

.TP
.B proxytemplate <template_string> <attrset_index> <ttl> 
Specifies a cacheable template and "time to live" (in sec) <ttl> of queries 
belonging to the template. 

.TP
.B response-callback { head | tail }
Specifies whether the response callback should be placed at the
.B tail
(the default) or at the 
.B 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 \fIafter\fP massaging the first
time, and \fIbefore\fP massaging when cached.

.LP
The following adds a template with filter string \fB((&sn=)(givenName=))\fP 
and attributes mail, postaladdress, telephonenumber and a TTL of 1 hour. 
.LP
.RS
.nf
proxyattrset \fB0 mail postaladdress telephonenumber\fP
proxytemplate \fB(&(sn=)(givenName=)) 0 3600\fP
.fi
.RE

.LP
Directives for configuring the underlying database must also be given, as
shown here:
.LP
.RS
.nf
directory /var/tmp/cache
cachesize 100
.fi
.RE
.LP
Any valid directives for the chosen database type may be used.
.SH FILES
.TP
ETCDIR/slapd.conf
default slapd configuration file
.SH SEE ALSO
.BR slapd.conf (5),
.BR slapd\-ldap (5),
.BR slapd\-meta (5),
.BR slapd\-sql (5),
.BR slapd (8).
.SH AUTHOR
Originally implemented by Apurva Kumar as an extension to back-meta;
turned into an overlay by Howard Chu.