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<!--Java sync-link--><h1 class="topictitle1">Module mod_cache</h1>
<div><div class="important"><span class="importanttitle">Important:</span> Information
for this topic supports the latest PTF levels for HTTP Server for i5/OS .
It is recommended that you install the latest PTFs to upgrade to the latest
level of the HTTP Server for i5/OS. Some of the topics documented here are
not available prior to this update. See <a href="http://www-03.ibm.com/servers/eserver/iseries/software/http/services/service.html" target="_blank">http://www.ibm.com/servers/eserver/iseries/software/http/services/service.htm</a> <img src="www.gif" alt="Link outside Information Center" /> for more information. </div>
<p><strong>Summary</strong></p>
<p>This module contains directives that define support for the HTTP Proxy
function which includes the proxy caching function.</p>
<div class="section"><h4 class="sectiontitle">Cache Expiry Times</h4><p>Cache expiry times are different
than expiry times provided in HTTP response data. Cache expiry times are calculated
by caching agents (such as a proxy server), whereas expiry times in HTTP response
data are provided by content servers (for example, via HTTP Expires headers).
If cacheable data from content servers contains expiry times, a caching agent
(or proxy) must use cache expiry times that are no later than the corresponding
data expiry times. In other words, caching agents may not serve data from
cache after it has expired, however they may stop serving it from cache prior
to such time. </p>
<p>If content servers do not provide expiry times for cacheable
data, the caching agent (or proxy) may try to use other response information
to calculate acceptable cache expiry times, or it may use some arbitrary default
value, as determined by the administrator.</p>
<div class="note"><span class="notetitle">Note:</span> Response data is considered
cacheable for the proxy function if it satisfies criteria described under <a href="#rzaiemod_cache__criteria">Criteria for Local Proxy Cache</a>.</div>
<p>The proxy
function follows these rules to determine which directive settings to use
to calculate cache expiry times for HTTP proxy response data stored in the
local proxy cache. </p>
<ol><li>If HTTP response data contains expiry times (via Expires header for HTTP
requests only) these times are also used as cache expiry times. </li>
<li>If HTTP response data does not contain expiry times, but does contain
information pertaining to when it was last modified (via Last-Modified header
for HTTP requests, or MDTM command for FTP requests), the CacheLastModifiedFactor
and CacheMaxExpire directive settings are used to calculate cache expiry times.
</li>
<li>If HTTP response data does not contain expiry times, nor does it contain
information pertaining to when it was last modified, the CacheDefaultExpire
directive setting is used to calculate arbitrary cache expiry times. </li>
</ol>
<div class="note"><span class="notetitle">Note:</span> The first rule has one exception. If response code 304 (Not Modified)
is received for HTTP requests, Expires headers (if any) are not used to set
new cache expiry time. The second rule is applied (for 304 responses) if last
modified times from cached data are available to recalculate new cache expiry
times. If last modified times are not available from cached data, the third
rule is applied.</div>
</div>
<div class="section" id="rzaiemod_cache__criteria"><a name="rzaiemod_cache__criteria"><!-- --></a><h4 class="sectiontitle">Criteria for Local Proxy Cache</h4><p>When
configured, the server handles certain requests using the proxy function to
obtain data from remote servers, which it then serves as HTTP proxy response
data. It does this when acting as either a forward proxy or a reverse proxy
(see ProxyRequests or ProxyReverse). By default, the proxy function obtains
and handles data separately for each request. The server may be made more
efficient, however, by using a local proxy cache to store HTTP proxy response
data locally, which it then serves multiple times for multiple requests. The
server is more efficient since remote servers need only be contacted when
data in the local proxy cache expires. </p>
<p>Not all response data obtained
by the server is cached and served for multiple requests, due mostly for reasons
involving privacy, version control (frequency of change), and negotiable content.
This type of response data is not considered cacheable and must be obtained
from remote servers for each request.</p>
<p><strong>Standard Criteria</strong></p>
<p>Standard
criteria for the server's local proxy cache and proxy function, in regards
to response data obtained using specified protocols, is described in the following
lists. This criteria is used to determine whether HTTP proxy response data
is cacheable and may be served multiple times for multiple requests. </p>
<p>HTTP
response data:</p>
<ul><li>Only data requested using the GET method is cacheable. </li>
<li>Only data received on a request that does not end with a '/' is cacheable. <ul><li>200 (OK) </li>
<li>203 (Non Authoritative) </li>
<li>300 (Multiple Choices) </li>
<li>301 (Moved Permanently) </li>
<li>304 (Not Modified) </li>
</ul>
</li>
<li>If data contains an Expires header, the header must be valid. <div class="note"><span class="notetitle">Note:</span> This
does not apply to data that does not contain an Expires header. </div>
</li>
<li>If data contains an Expires header, the header must not specify a time
that has already past (according to local system time). </li>
<li>If data contains an Expires header, the expiration time must be greater
than the configured minimum expiration time. </li>
<li>Data received with response code 200 (OK) must contain either a Last-Modified
header or an ETag header. This requirement is waived if on is specified for
the CacheIgnoreNoLastMod directive. </li>
<li>Data received with response code 304 (Not Modified) is not cacheable if
a previous version is not already in cache. </li>
<li>If data contains a Cache-Control header, the header must not specify the
value "no-store" or "private". </li>
<li>If data contains a Pragma header, the header must not specify the value
"no-cache". </li>
<li>If the request provides an Authorization header (possibly used by the
remote server), response data must contain a Cache-Control header that specifies
one or more of the following values: "s-maxage", "must-revalidate" or "public".
</li>
<li>If data contains a Content-Length header, the header must not specify
a value that exceeds the minimum or maximum data size limits set by the CacheMinFileSize
and CacheMaxFileSize directives. See Additional Criteria for more information.</li>
</ul>
<p>FTP response data: </p>
<ul><li>Only data requested using the GET method is cacheable. </li>
<li>Data is only cached if LIST or RETR commands return one of the following
response codes: <ul><li>125 (OK, Data Transfer Starting) </li>
<li>150 (OK, Opening Data Connection) </li>
<li>226 (OK, Closing Data Connection) </li>
<li>250 (OK)</li>
</ul>
<div class="note"><span class="notetitle">Note:</span> The LIST command is used to retrieve directory listings. The RETR
command is used to retrieve data files.</div>
</li>
<li>Data must contain information for an HTTP Last-Modified header (produced
via MDTM command with response code 213, see Notes: below). This requirement
is waived if on is specified for the CacheIgnoreNoLastMod directive. </li>
<li>If data contains information for an HTTP Content-Length header (produced
via SIZE command with response code 213), the header must not specify a value
that exceeds the minimum or maximum data size limits set by the CacheMinFileSize
and CacheMaxFileSize directives, respectively. See Additional Criteria for
more information. </li>
</ul>
<p>HTTPS (or SSL-tunneling over HTTP) response data: </p>
<ul><li>Data requested using SSL-tunneling over HTTP is not cacheable. </li>
</ul>
<p>No other protocols are supported by the proxy function. </p>
<p><strong>Additional
Criteria </strong></p>
<p>Additional criteria for the server's local proxy cache
and proxy functions may be imposed by the function providing underlying cache
support. Currently, this includes only the disk cache function. </p>
<p>The
following list describes additional restrictions on HTTP proxy response data
stored in a local proxy cache, imposed by the mod_disk_cache module: </p>
<ul><li>Cache data must not exceed the minimum or maximum data size limits set
by the CacheMinFileSize and CacheMaxFileSize directives. This restriction
applies regardless of Content-Length header values (if any) in HTTP proxy
response data. </li>
<li>Data with cache expiry times that will expire within the minimum time
margin set by the CacheTimeMargin directive is not cached. This restriction
applies to HTTP proxy response data, using cache expiry times calculated according
to rules described in the Cache Expiry Times. See mod_disk_cache for other
restriction that may apply. </li>
</ul>
</div>
<p><strong>Directives</strong></p>
<ul><li><a href="#cachedefaultexpire">CacheDefaultExpire</a> </li>
<li><a href="#cacheexpirycheck">CacheExpiryCheck</a> </li>
<li><a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a> </li>
<li><a href="#cacheignorenolastmod">CacheIgnoreNoLastMod</a> </li>
<li><a href="#cachelastmodifiedfactor">CacheLastModifiedFactor</a> </li>
<li><a href="#cachemaxexpire">CacheMaxExpire</a> </li>
<li><a href="#cachemaxfilesize">CacheMaxFileSize</a> </li>
<li><a href="#cacheminfilesize">CacheMinFileSize</a> </li>
<li><a href="#cachetimemargin">CacheTimeMargin</a></li>
</ul>
</div>
<div class="hr" id="cachedefaultexpire"><a name="cachedefaultexpire"><!-- --></a><h2 class="topictitle2">CacheDefaultExpire </h2>
<div>
<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="void" border="0" rules="none"><tbody><tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Module">Module</a></strong>: mod_cache </td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Syntax">Syntax</a></strong>: CacheDefaultExpire <em>period</em> </td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Default">Default</a></strong>: CacheDefaultExpire 3600</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Context">Context</a></strong>: <span id="cachedefaultexpire__cachedefaultexpire_context"><a name="cachedefaultexpire__cachedefaultexpire_context"><!-- --></a>server
config, virtual host </span></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Override">Override</a></strong>: none </td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Origin">Origin</a></strong>: <span id="cachedefaultexpire__cachedefaultexpire_origin"><a name="cachedefaultexpire__cachedefaultexpire_origin"><!-- --></a>Apache</span></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__UsageConsiderations">Usage Considerations</a></strong>: A LoadModule is required in
the configuration file prior to using the directive. The statement should
be as follows: <samp class="codeph">LoadModule cache_module /QSYS.LIB/QHTTPSVR.LIB/QZSRCORE.SRVPGM</samp></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Example">Example</a></strong>: CacheDefaultExpire 3 </td>
</tr>
</tbody>
</table>
</div>
<p>The CacheDefaultExpire directive specifies the default number of seconds
in which cacheable HTTP proxy response data will be set to expire within the
local proxy cache, starting from the time it is obtained by the server.</p>
<blockquote><dl><dt class="dlterm"><strong>Parameter</strong>: <em>period </em></dt>
<dd><ul><li>The <em>period</em> parameter defines the default cache expiry period, in
seconds. </li>
</ul>
</dd>
</dl>
<p>This setting is used to calculate arbitrary cache expiry
times for HTTP proxy response data stored in the local proxy cache. See Cache
Expiry Times for more information on how the server determines which settings
to use to calculate cache expiry times. See the CacheIgnoreNoLastMod directive
for information relating to how cache criteria may be waived for this setting
to take affect. </p>
<p>If this setting is used, cache expiry times are calculated
by adding the specified number of seconds to the time that data is received
by the proxy function. </p>
<dl><dt class="dlterm"><strong>Example</strong>:</dt>
<dd><pre>ProxyRequests on
CacheRoot proxyCache
CacheDefaultExpire 3600
CacheMaxExpire 86400
CacheLastModifiedFactor 0.3</pre>
</dd>
</dl>
</blockquote>
<p>In the example, if a cacheable data is retrieved from a server that does
not provide an expiry time (via HTTP Expires header), nor does it indicate
when the data was last modified (via HTTP Last-Modified header, or FTP MDTM
command), the server will cache and serve the data for 3600 seconds (since
CacheDefaultExpire is set to 3600 and "on" is specified for CacheIgnoreNoLastMod).
If an expiry time or last-modified time is provided, CacheDefaultExpire would
not be used (see Cache Expiry Times). </p>
<div class="note"><span class="notetitle">Note:</span> Response data is considered cacheable for the proxy function if it satisfies
criteria described under Criteria for Local Proxy Cache.</div>
<ul><li>Setting ProxyRequests and ProxyReverse to off negates this directive.
</li>
<li>Setting ProxyNoConnect to on negates this directive. </li>
<li>This directive is used only if CacheRoot is set. </li>
</ul>
</div>
</div>
<div class="hr" id="cacheexpirycheck"><a name="cacheexpirycheck"><!-- --></a><h2 class="topictitle2">CacheExpiryCheck</h2>
<div>
<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="void" border="0" rules="none"><tbody><tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Module">Module</a></strong>: mod_cache </td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Syntax">Syntax</a></strong>: CacheExpiryCheck <em>on | off </em></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Default">Default</a></strong>: CacheExpiryCheck on </td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Context">Context</a></strong>: <span id="cacheexpirycheck__cacheexpirycheck_context"><a name="cacheexpirycheck__cacheexpirycheck_context"><!-- --></a>server
config, virtual host </span></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Override">Override</a></strong>: none </td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Origin">Origin</a></strong>: <span id="cacheexpirycheck__cacheexpirycheck_origin"><a name="cacheexpirycheck__cacheexpirycheck_origin"><!-- --></a>iSeries™ </span></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__UsageConsiderations">Usage Considerations</a></strong>: A LoadModule is required in
the configuration file prior to using the directive. The statement should
be as follows: <samp class="codeph">LoadModule cache_module /QSYS.LIB/QHTTPSVR.LIB/QZSRCORE.SRVPGM</samp></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Example">Example</a></strong>: CacheExpiryCheck on</td>
</tr>
</tbody>
</table>
</div>
<p>The CacheExpiryCheck directive specifies whether the server is to observe
cache expiry times when cached data is requested using the disk cache function
(see CacheRoot). </p>
<blockquote><dl><dt class="dlterm"><strong>Parameter</strong>: <em>on | off </em></dt>
<dd><ul><li>If <em>on</em> is specified (the default), the server will perform and apply
all cache expiry time checks for data currently available in cache. </li>
<li>If <em>off</em> is specified, cache expiry times will not be observed and
cached data (if any) will always be available. </li>
</ul>
</dd>
</dl>
</blockquote>
<p>Cache expiry time checks may be disabled (off) when the content of the
cache is managed by an application or process other than the server itself.
If the content of the cache is not managed by an application or process other
than the server, this setting must be set to on (the default) to prevent the
disk cache function from making expired data appear valid. </p>
<div class="note"><span class="notetitle">Note:</span> When the disk cache function is used to support a local proxy cache,
this setting determines whether cache expiry times are observed for the proxy
function. Once cached, data is usually available from cache until its respective
cache expiry times has passed. However, if cache expiry time checks are disabled
(CacheExpiryCheck off), the proxy function will serve cached HTTP proxy response
data regardless of whether it has expired. This effectively causes the disk
cache function to ignore cache expiry times calculated using the CacheDefaultExpire,
CacheMaxExpire, and CacheLastModifiedFactor directives for a local proxy cache,
as well as any expiry time provided via Expires headers (for HTTP requests). </div>
<p>See the CacheRoot directive for more information on how the disk cache
function is used to support a local proxy cache. </p>
</div>
</div>
<div class="hr" id="cacheignorecachecontrol"><a name="cacheignorecachecontrol"><!-- --></a><h2 class="topictitle2">CacheIgnoreCacheControl</h2>
<div>
<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="void" border="0" rules="none"><tbody><tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Module">Module</a></strong>: mod_cache </td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Syntax">Syntax</a></strong>: CacheIgnoreCacheControl <em>on | off </em></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Default">Default</a></strong>: CacheIgnoreCacheControl off </td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Context">Context</a></strong>: <span id="cacheignorecachecontrol__cacheignorecachecontrol_context"><a name="cacheignorecachecontrol__cacheignorecachecontrol_context"><!-- --></a>server
config, virtual host </span></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Override">Override</a></strong>: none </td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Origin">Origin</a></strong>: <span id="cacheignorecachecontrol__cacheignorecachecontrol_origin"><a name="cacheignorecachecontrol__cacheignorecachecontrol_origin"><!-- --></a>Apache</span></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__UsageConsiderations">Usage Considerations</a></strong>: A LoadModule is required in
the configuration file prior to using the directive. The statement should
be as follows: <samp class="codeph">LoadModule cache_module /QSYS.LIB/QHTTPSVR.LIB/QZSRCORE.SRVPGM</samp></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Example">Example</a></strong>: CacheIgnoreCacheControl on </td>
</tr>
</tbody>
</table>
</div>
<p>The CacheIgnoreCacheControl directive specifies whether the server is to
observe certain cache controlling request headers (for example, Cache-Control
and Pragma) when handling requests using the proxy function. </p>
<blockquote><dl><dt class="dlterm"><strong>Parameter</strong>: <em>on | off </em></dt>
<dd><ul><li>If <em>on</em> is specified, the server will not observe cache controlling
request headers. </li>
<li>If <em>off</em> is specified (the default), the server will observe cache
controlling request headers when HTTP proxy response data is available from
the local proxy cache. </li>
</ul>
</dd>
</dl>
</blockquote>
<p>By default, the server observes certain cache controlling request headers
(for example, "Cache-Control : no-store" and "Pragma : no-cache") when handling
requests using the proxy function. If such headers are present in HTTP request
data sent to the server, the proxy function will not serve HTTP proxy response
data from the local proxy cache since these headers indicate that cached data
is not wanted. However, if on is specified for this setting, the proxy function
will ignore cache controlling request headers and serve HTTP proxy response
data from cache, if it is available. </p>
<ul><li>Setting ProxyRequests and ProxyReverse to off negates this directive.
</li>
<li>This directive is used only if CacheRoot is set. </li>
</ul>
</div>
</div>
<div class="hr" id="cacheignorenolastmod"><a name="cacheignorenolastmod"><!-- --></a><h2 class="topictitle2">CacheIgnoreNoLastMod</h2>
<div>
<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="void" border="0" rules="none"><tbody><tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Module">Module</a></strong>: mod_cache </td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Syntax">Syntax</a></strong>: CacheIgnoreNoLastMod <em>on | off </em></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Default">Default</a></strong>: CacheIgnoreNoLastMod off </td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Context">Context</a></strong>: <span id="cacheignorenolastmod__cacheignorenolastmod_context"><a name="cacheignorenolastmod__cacheignorenolastmod_context"><!-- --></a>server
config, virtual host </span></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Override">Override</a></strong>: none </td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Origin">Origin</a></strong>: <span id="cacheignorenolastmod__cacheignorenolastmod_origin"><a name="cacheignorenolastmod__cacheignorenolastmod_origin"><!-- --></a>Apache</span></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__UsageConsiderations">Usage Considerations</a></strong>: A LoadModule is required in
the configuration file prior to using the directive. The statement should
be as follows: <samp class="codeph">LoadModule cache_module /QSYS.LIB/QHTTPSVR.LIB/QZSRCORE.SRVPGM</samp></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Example">Example</a></strong>: CacheIgnoreNoLastMod on </td>
</tr>
</tbody>
</table>
</div>
<p>The CacheIgnoreNoLastMod directive specifies whether the server may cache
HTTP proxy response data in the local proxy cache, if it does not contain
a Last-Modified header or an ETag header. </p>
<blockquote><dl><dt class="dlterm"><strong>Parameter</strong>: <em>on | off </em></dt>
<dd><ul><li>If <em>off</em> is specified (the default), the server requires either an
ETag header or a Last-Modified header to be present in all HTTP proxy response
data cached in the local proxy cache. </li>
<li>If <em>on</em> is specified, the server will not require an ETag header
or Last-Modified header to be present in HTTP proxy response data cached in
the local proxy cache. </li>
</ul>
<p>By default, if data does not contain either an ETag header or a Last-Modified
header, the server does not consider it cacheable. Specifying on for this
setting waives this criteria. See Criteria for Local Proxy Cache for more
information. </p>
</dd>
</dl>
<dl><dt class="dlterm"><strong>Example One</strong>:</dt>
<dd><pre>ProxyRequests on
CacheRoot proxyCache
CacheIgnoreNoLastMod off
CacheDefaultExpire 1</pre>
<p>In the example, if data is received from
a server that does not provide an expiry time (via HTTP Expires header), nor
does it have an ETag or Last-Modified header, it is not considered cacheable
since off is specified for CacheIgnoreNoLastMod. The server serves the data
for the current request, but does not cache it for subsequent requests. The
settings for CacheDefaultExpire is not used. </p>
</dd>
</dl>
<dl><dt class="dlterm"><strong>Example Two</strong>:</dt>
<dd><pre>ProxyRequests on
CacheRoot proxyCache
CacheIgnoreNoLastMod on
CacheDefaultExpire 1</pre>
<p>In this example, if data is received from
a server that does not provide an expiry time (via HTTP Expires header), nor
does it have an ETag or Last-Modified header (as in example one), it is still
considered cacheable since on is specified for CacheIgnoreNoLastMod. The server
serves the data for the current request, and may calculate a cache expiry
time using CacheDefaultExpire to cache it for subsequent requests, assuming
it satisfies all other cache criteria. </p>
</dd>
</dl>
</blockquote>
<div class="note"><span class="notetitle">Note:</span> Response data is considered cacheable for the proxy function if it satisfies
criteria described under Criteria for Local Proxy Cache.</div>
<ul><li>Setting ProxyRequests and ProxyReverse to off negates this directive.
</li>
<li>Setting ProxyNoConnect to on negates this directive. </li>
<li>This directive is used only if CacheRoot is set. </li>
</ul>
</div>
</div>
<div class="hr" id="cachelastmodifiedfactor"><a name="cachelastmodifiedfactor"><!-- --></a><h2 class="topictitle2">CacheLastModifiedFactor</h2>
<div>
<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="void" border="0" rules="none"><tbody><tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Module">Module</a></strong>: mod_cache </td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Syntax">Syntax</a></strong>: CacheLastModifiedFactor <em>factor</em> </td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Default">Default</a></strong>: CacheLastModifiedFactor 0.1 </td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Context">Context</a></strong>: <span id="cachelastmodifiedfactor__cachelastmodifiedfactor_context"><a name="cachelastmodifiedfactor__cachelastmodifiedfactor_context"><!-- --></a>server
config, virtual host </span></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Override">Override</a></strong>: none </td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Origin">Origin</a></strong>: <span id="cachelastmodifiedfactor__cachelastmodifiedfactor_origin"><a name="cachelastmodifiedfactor__cachelastmodifiedfactor_origin"><!-- --></a>Apache </span></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__UsageConsiderations">Usage Considerations</a></strong>: A LoadModule is required in
the configuration file prior to using the directive. The statement should
be as follows: <samp class="codeph">LoadModule cache_module /QSYS.LIB/QHTTPSVR.LIB/QZSRCORE.SRVPGM</samp></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Example">Example</a></strong>: CacheLastModifiedFactor 0.3</td>
</tr>
</tbody>
</table>
</div>
<p>The CacheLastModifiedFactor directive specifies a multiplication factor
used in the formula: </p>
<blockquote><pre>period = time-since-last-modification *&lt;factor&gt;</pre>
</blockquote>
<blockquote><dl><dt class="dlterm"><strong>Parameter</strong>: <em>factor </em></dt>
<dd><ul><li>The <em>factor</em> parameter specifies the multiplication factor used in
the formula (described above) to calculate cache expiry times. </li>
</ul>
<p>This formula is used and setting is used along with CacheMaxExpire
to calculate cache expiry times for HTTP proxy response data store in the
local proxy cache, based on when the data was last modified. See Cache Expiry
Times for more information on how the server determines which settings to
use when calculating cache expiry times. </p>
<p>If this setting is used,
cache expiry times are calculated by adding the lesser of the calculated period
(using the formula above) and the period specified for CacheMaxExpire to the
time that data is received by the proxy function. Using this method, data
that has not changed recently is served from cache longer than data that has
changed recently, since its last-modified time is older and will produce a
greater cache expiry period. This assumes that both responses yield calculated
cache expiry periods that are less than the CacheMaxExpire directive setting. </p>
</dd>
</dl>
<dl><dt class="dlterm"><strong>Example</strong>:</dt>
<dd><pre>ProxyRequests on
CacheRoot proxyCache
CacheMaxExpire 86400
CacheLastModifiedFactor 0.3</pre>
<p>In this example, if cacheable data
is received from a server that does not provide an expiry time (via HTTP Expires
header), but does indicate that the data was last changed 10 hours ago (via
HTTP Last-Modified header, or FTP MDTM command), the server would calculate
a period of 3 hours using CacheLastModifiedFactor (10 * 0.3) and would cache
and serve the data for the same period of time since it is less than the maximum
limit of 24 hours set by CacheMaxExpire. </p>
</dd>
</dl>
</blockquote>
<div class="note"><span class="notetitle">Note:</span> Response data is considered cacheable for the proxy function if it satisfies
criteria described under Criteria for Local Proxy Cache.</div>
<p>If a similar response for this example indicates that the data was last
changed 8 days ago (or 192 hours), the server would calculate a period of
57.6 hours using CacheLastModifiedFactor (192 * 0.3), but it would cache and
serve the data for a period of only 24 hours since CacheMaxExpire sets a limit
on the maximum period for the CacheLastModifiedFactor formula. </p>
<ul><li>Setting ProxyRequests and ProxyReverse to off negates this directive.
</li>
<li>Setting ProxyNoConnect to on negates this directive. </li>
<li>This directive is used only if CacheRoot is set. </li>
</ul>
</div>
</div>
<div class="hr" id="cachemaxexpire"><a name="cachemaxexpire"><!-- --></a><h2 class="topictitle2">CacheMaxExpire</h2>
<div>
<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="void" border="0" rules="none"><tbody><tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Module">Module</a></strong>: mod_cache</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Syntax">Syntax</a></strong>: CacheMaxExpire <var class="varname">period</var></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Default">Default</a></strong>: CacheMaxExpire 86400</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Context">Context</a></strong>: server config, virtual host</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Override">Override</a></strong>: none</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Origin">Origin</a></strong>: Apache</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__UsageConsiderations">Usage Considerations</a></strong>: A LoadModule is required in
the configuration file prior to using the directive. The statement should
be as follows: <samp class="codeph">LoadModule cache_module /QSYS.LIB/QHTTPSVR.LIB/QZSRCORE.SRVPGM</samp></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Example">Example</a></strong>: CacheMaxExpire 43200</td>
</tr>
</tbody>
</table>
</div>
<p> The CacheMaxExpire directive specifies the maximum number of seconds in
which cacheable HTTP proxy response data will be set to expire within the
local proxy cache (when the CacheLastModifiedFactor directive setting is used).
This setting has no affect on other settings used to calculate cache expiry
times.</p>
<blockquote><dl><dt class="dlterm"><strong>Parameter</strong>: <em>period</em></dt>
<dd><ul><li> The <var class="varname">period</var> parameter specifies the maximum cache expiry
period, in seconds, that may be used when expiry times are calculated using
the CacheLastModifiedFactor directive setting.<p>This setting is used along
with the CacheLastModifiedFactor directive setting to calculate expiry times
for HTTP proxy response data stored in the local proxy cache, based on when
data was last modified. See Cache Expiry Times for more information on how
the server determines which settings to use when calculating cache expiry
times. If this setting is used, cache expiry times are calculated by adding
the lesser of the specified period and the period calculated using CacheLastModifiedFactor
to the time that data is received by the proxy function.</p>
</li>
</ul>
</dd>
</dl>
<dl><dt class="dlterm"><strong>Example</strong></dt>
<dd><pre>ProxyRequests on
CacheRoot proxyCache
CacheMaxExpire 86400
CacheLastModifiedFactor 0.3</pre>
<p>In this example, if cacheable data
is received from a server that does not provide an expiry time (via HTTP Expires
header), but does indicate that the data was last changed 5 days ago (via
HTTP Last-Modified header, or FTP MDTM command), the server would calculate
a period of 1.5 days using CacheLastModifiedFactor (5 * 0.3), but it would
cache and serve the data for a period of only 86400 seconds (1 day) since
CacheMaxExpire sets a maximum limit of 86400 seconds.</p>
</dd>
</dl>
</blockquote>
<div class="note"><span class="notetitle">Note:</span> Response data is considered cacheable for the proxy function if it satisfies
criteria described under Criteria for Local Proxy Cache.</div>
<ul><li></li>
<li>Setting ProxyRequests and ProxyReverse to off negates this directive.</li>
<li>Setting ProxyNoConnect to on negates this directive.</li>
<li>This directive is used only if CacheRoot is set</li>
</ul>
</div>
</div>
<div class="hr" id="cachemaxfilesize"><a name="cachemaxfilesize"><!-- --></a><h2 class="topictitle2">CacheMaxFileSize</h2>
<div>
<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="void" border="0" rules="none"><tbody><tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Module">Module</a></strong>: mod_cache</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Syntax">Syntax</a></strong>: CacheMaxFileSize <var class="varname">size</var></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Default">Default</a></strong>: CacheMaxFileSize 1000000</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Context">Context</a></strong>: server config, virtual host</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Override">Override</a></strong>: none </td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Origin">Origin</a></strong>: Apache</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__UsageConsiderations">Usage Considerations</a></strong>: A LoadModule is required in
the configuration file prior to using the directive. The statement should
be as follows:<samp class="codeph"> LoadModule cache_module /QSYS.LIB/QHTTPSVR.LIB/QZSRCORE.SRVPGM,
disk_cache_module /QSYS.LIB/QHTTPSVR.LIB/QZSRCORE.SRVPGM</samp></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Example">Example</a></strong>: CacheMaxFileSize 4000000</td>
</tr>
</tbody>
</table>
</div>
<p>The CacheMaxFileSize directive specifies the maximum amount of data that
may be stored in the proxy disk cache for a single URL, in bytes. This setting
effectively placing a maximum data size limit on individual cache entries.
If the disk cache function is disabled (see CacheRoot), this setting has no
affect.</p>
<blockquote><dl><dt class="dlterm"><strong>Parameter</strong>: <em>size</em></dt>
<dd><ul><li>The <var class="varname">size</var> parameter specifies the maximum number of
bytes allowed for cache data entries.<p>A minimum document size limits specified
using CacheMinFileSize.</p>
<p><strong>Notes for local proxy cache:</strong></p>
<p>When
the disk cache function is used to support a local proxy cache, this setting
places a maximum data size limit on HTTP proxy responses which remain in the
cache after cache maintenance has run. See the CachGcDaily or CacheGcInterval
directives for more information on how the disk cache maintenance function
is used to support a local proxy cache.</p>
</li>
</ul>
</dd>
</dl>
<dl><dt class="dlterm"><strong>Example</strong></dt>
<dd><pre>ProxyRequests on
CacheRoot proxyCache
CacheMaxFileSize 5000000
CacheMinFileSize 400000</pre>
<p>For this example, if 7.2 megabytes of
cacheable HTTP proxy response data is available for a single proxy request
but will be removed during the next cache maintenance cycle since it is larger
than the 5000000 byte maximum data size limit imposed by CacheMaxFileSize.
A 3.8 megabyte HTTP proxy response may be cached for subsequent proxy requests
and will remain in the cache after the cache maintenance cycle has run since
it is smaller than the 5000000 byte maximum data size limit and larger than
the 400000 byte minimum data size limit (set by CacheMinFileSize).</p>
</dd>
</dl>
</blockquote>
<p>If the values specified for CacheMinFileSize and CacheMaxFileSize are changed
once they have been used to cache data, the server will discard existing cache
data that does not adhere to the new limits when it runs disk cache maintenance.
See CachGcDaily or CacheGcInterval for more details on the disk cache maintenance
process.</p>
</div>
</div>
<div class="hr" id="cacheminfilesize"><a name="cacheminfilesize"><!-- --></a><h2 class="topictitle2">CacheMinFileSize</h2>
<div>
<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="void" border="0" rules="none"><tbody><tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Module">Module</a></strong>: mod_cache</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Syntax">Syntax</a></strong>: CacheMinFileSize <var class="varname">size</var></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Default">Default</a></strong>: CacheMinFileSize 1</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Context">Context</a></strong>: server config, virtual host</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Override">Override</a></strong>: none</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Origin">Origin</a></strong>: Apache</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__UsageConsiderations">Usage Considerations</a></strong>: A LoadModule is required in
the configuration file prior to using the directive. The statement should
be as follows: LoadModule cache_module /QSYS.LIB/QHTTPSVR.LIB/QZSRCORE.SRVPGM, <samp class="codeph">LoadModule
disk_cache_module /QSYS.LIB/QHTTPSVR.LIB/QZSRCORE.SRVPGM</samp></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Example">Example</a></strong>: CacheMinFileSize 40</td>
</tr>
</tbody>
</table>
</div>
<p> The CacheMinFileSize directive specifies the minimum amount of data that
may be stored in the proxy disk cache for a single URL, in bytes. This setting
effectively places a minimum data size limit on individual cache entries.
If the disk cache function is disabled (see CacheRoot), this setting has no
affect.</p>
<blockquote><dl><dt class="dlterm"><strong>Parameter</strong>: <em>size</em></dt>
<dd><ul><li> The <var class="varname">size</var> parameter specifies the minimum number of
bytes allowed for cache data entries.<p>A maximum document size limits specified
using CacheMaxFileSize.</p>
</li>
</ul>
</dd>
</dl>
<p><strong>Notes for local proxy cache:</strong></p>
<p>When the disk
cache function is used to support a local proxy cache, this setting places
a minimum data size limit on HTTP proxy responses which remain in the cache
after cache maintenance has run. See CachGcDaily and CacheGcInterval directives
for more details on the how the disk cache maintenance function is used to
support a local proxy cache.</p>
<dl><dt class="dlterm"><strong>Example</strong></dt>
<dd><pre>ProxyRequests on
CacheRoot proxyCache
CacheMaxFileSize 5000000
CacheMinFileSize 400000</pre>
<p>For this example, if 240 kilobytes of
cacheable HTTP proxy response data is available for a single proxy request,
but will be removed during the next cache maintenance cycle since it is less
than the 400000 byte minimum data size limit imposed by CacheMinFileSize.
A 2.7 megabyte HTTP proxy response may be cached for subsequent proxy requests
and will remain in the cache after the cache maintenance cycle has run since
it is larger than the 400000 byte minimum data size limit and smaller than
the 5000000 byte maximum data size limit (set by CacheMaxFileSize).</p>
</dd>
</dl>
</blockquote>
<p>If the values specified for CacheMinFileSize and CacheMaxFileSize are changed
once they have been used to cache data, the server will discard existing cache
data that does not adhere to the new limits when it runs disk cache maintenance.
See CachGcDaily or CacheGcInterval for more details on the disk cache maintenance
process.</p>
<ul><li>If set greater than CacheMaxFileSize, the size parameter will be ignored
and the default value will be used.</li>
<li>The default for this directive is dependent on the value set for CacheMaxFileSize.
If CacheMaxFileSize is set greater than 200 the default for this directive
is 200, otherwise the default is 0.</li>
</ul>
</div>
</div>
<div class="hr" id="cachetimemargin"><a name="cachetimemargin"><!-- --></a><h2 class="topictitle2">CacheTimeMargin</h2>
<div>
<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="void" border="0" rules="none"><tbody><tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Module">Module</a></strong>: mod_cache</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Syntax">Syntax</a></strong>: CacheTimeMargin <var class="varname">period</var></td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Default">Default</a></strong>: CacheTimeMargin 120</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Context">Context</a></strong>: server config, virtual host</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Override">Override</a></strong>: none</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Origin">Origin</a></strong>: Apache</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__UsageConsiderations">Usage Considerations</a></strong>: A LoadModule is required in
the configuration file prior to using the directive. The statement should
be as follows:<pre>LoadModule cache_module /QSYS.LIB/QHTTPSVR.LIB/QZSRCORE.SRVPGM
LoadModule disk_cache_module /QSYS.LIB/QHTTPSVR.LIB/QZSRCORE.SRVPGM</pre>
</td>
</tr>
<tr><td colspan="2" valign="top"><strong><a href="rzaiedirective-dict.htm#rzaiedirective-dict__Example">Example</a></strong>: CacheTimeMargin 300</td>
</tr>
</tbody>
</table>
</div>
<p> The CacheTimeMargin directive specifies the minimum number of seconds
remaining prior to data expiration, as indicated in the expires response header,
in order for data to be cached by the server using the disk cache function.
If the disk cache function is disabled (see CacheRoot), this setting has no
affect.</p>
<blockquote><dl><dt class="dlterm"><strong>Parameter</strong>: <em>period</em></dt>
<dd><ul><li> The <var class="varname">period</var> parameter specifies the minimum time margin
for cache update requests (in seconds).<p>The server calculates cache time
margins (or periods) for cache update requests by subtracting the current
system time from the computed expiry time. Data for cache update requests
that produce cache time margins, that are less than the specified minimum
time margin is not cached by the server.</p>
</li>
</ul>
</dd>
</dl>
<p><strong>Notes for local proxy cache:</strong></p>
<p>The disk cache
function uses CacheDefaultExpire, CacheLastModifiedFactor, and CacheMaxExpire
directives which may produce cache time margins that are less than the minimum
time margin specified by the CacheTimeMargin directive. In this case, the
CacheTimeMargin directive will also be used to determine if the file will
be cached. See the CacheRoot directive for more information on how the disk
cache function is used to support a local proxy cache.</p>
<dl><dt class="dlterm"><strong>Example</strong></dt>
<dd><pre>ProxyRequests on
CacheRoot proxyCache
CacheTimeMargin 120</pre>
</dd>
</dl>
</blockquote>
<p>In this example, if cacheable HTTP proxy response data is available, the
data will be served (by proxy), but it will not be cached for subsequent proxy
requests if set to expire in less than 120 seconds (CacheTimeMargin 120).
If the HTTP proxy response data is set to expire in more than two minutes,
the data will be served (by proxy) and will also be cached for subsequent
proxy requests.</p>
</div>
</div>
</body>
</html>
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