--- docs/manual/mod/directives.html.en	(revision 1696322)
+++ docs/manual/mod/directives.html.en	(working copy)
@@ -592,6 +592,7 @@ 
 <li><a href="mod_session_dbd.html#sessiondbdupdatelabel">SessionDBDUpdateLabel</a></li>
 <li><a href="mod_session.html#sessionenv">SessionEnv</a></li>
 <li><a href="mod_session.html#sessionexclude">SessionExclude</a></li>
+<li><a href="mod_session.html#sessionexpiryupdateinterval">SessionExpiryUpdateInterval</a></li>
 <li><a href="mod_session.html#sessionheader">SessionHeader</a></li>
 <li><a href="mod_session.html#sessioninclude">SessionInclude</a></li>
 <li><a href="mod_session.html#sessionmaxage">SessionMaxAge</a></li>
--- docs/manual/mod/mod_session.xml	(revision 1696322)
+++ docs/manual/mod/mod_session.xml	(working copy)
@@ -487,4 +487,41 @@ 
 </usage>
 </directivesynopsis>
 
+<directivesynopsis>
+<name>SessionExpiryUpdateInterval</name>
+<description>Define the number of seconds a session's expiry may change without
+being written</description>
+<syntax>SessionExpiryUpdateInterval <var>interval</var></syntax>
+<default>SessionExpiryUpdateInterval 0</default>
+<contextlist><context>server config</context>
+<context>virtual host</context>
+<context>directory</context>
+<context>.htaccess</context>
+</contextlist>
+
+<usage>
+    <p>The <directive>SessionExpiryUpdateInterval</directive> directive allows
+    sessions to avoid the cost associated with writing the session each request
+    when only the expiry time has changed. This can be used to make a website
+    more efficient or reduce load on a database when using
+    <module>mod_session_dbd</module>. The session is always written if the data
+    stored in the session has changed or the expiry has changed by more than the
+    configured interval.</p>
+
+    <p>Setting the interval to zero disables this directive, and the session
+    expiry is refreshed each request.</p>
+
+    <p>This directive only has an effect when combined with
+    <directive module="mod_session">SessionMaxAge</directive> to enable session
+    expiry. Sessions without an expiry are only written when the data stored in
+    the session has changed.</p>
+
+    <note type="warning"><title>Warning</title>
+    <p>Because the session expiry may not be refreshed with each request, it's
+    possible for sessions to expire up to <var>interval</var> seconds early.
+    Using a small interval usually provides sufficient savings while having a
+    minimal effect on expiry resolution.</p></note>
+</usage>
+</directivesynopsis>
+
 </modulesynopsis>
--- docs/manual/mod/mod_session.html.en	(revision 1696322)
+++ docs/manual/mod/mod_session.html.en	(working copy)
@@ -78,6 +78,7 @@ 
 <li><img alt="" src="../images/down.gif" /> <a href="#session">Session</a></li>
 <li><img alt="" src="../images/down.gif" /> <a href="#sessionenv">SessionEnv</a></li>
 <li><img alt="" src="../images/down.gif" /> <a href="#sessionexclude">SessionExclude</a></li>
+<li><img alt="" src="../images/down.gif" /> <a href="#sessionexpiryupdateinterval">SessionExpiryUpdateInterval</a></li>
 <li><img alt="" src="../images/down.gif" /> <a href="#sessionheader">SessionHeader</a></li>
 <li><img alt="" src="../images/down.gif" /> <a href="#sessioninclude">SessionInclude</a></li>
 <li><img alt="" src="../images/down.gif" /> <a href="#sessionmaxage">SessionMaxAge</a></li>
@@ -411,6 +412,40 @@ 
 
 </div>
 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<div class="directive-section"><h2><a name="SessionExpiryUpdateInterval" id="SessionExpiryUpdateInterval">SessionExpiryUpdateInterval</a> <a name="sessionexpiryupdateinterval" id="sessionexpiryupdateinterval">Directive</a></h2>
+<table class="directive">
+<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Define the number of seconds a session's expiry may change without
+being written</td></tr>
+<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>SessionExpiryUpdateInterval <var>interval</var></code></td></tr>
+<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>SessionExpiryUpdateInterval 0</code></td></tr>
+<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
+<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
+<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_session</td></tr>
+</table>
+    <p>The <code class="directive">SessionExpiryUpdateInterval</code> directive allows
+    sessions to avoid the cost associated with writing the session each request
+    when only the expiry time has changed. This can be used to make a website
+    more efficient or reduce load on a database when using
+    <code class="module"><a href="../mod/mod_session_dbd.html">mod_session_dbd</a></code>. The session is always written if the data
+    stored in the session has changed or the expiry has changed by more than the
+    configured interval.</p>
+
+    <p>Setting the interval to zero disables this directive, and the session
+    expiry is refreshed each request.</p>
+
+    <p>This directive only has an effect when combined with
+    <code class="directive"><a href="#sessionmaxage">SessionMaxAge</a></code> to enable session
+    expiry. Sessions without an expiry are only written when the data stored in
+    the session has changed.</p>
+
+    <div class="warning"><h3>Warning</h3>
+    <p>Because the session expiry may not be refreshed with each request, it's
+    possible for sessions to expire up to <var>interval</var> seconds early.
+    Using a small interval usually provides sufficient savings while having a
+    minimal effect on expiry resolution.</p></div>
+
+</div>
+<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 <div class="directive-section"><h2><a name="SessionHeader" id="SessionHeader">SessionHeader</a> <a name="sessionheader" id="sessionheader">Directive</a></h2>
 <table class="directive">
 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Import session updates from a given HTTP response header</td></tr>
--- modules/session/mod_session.c	(revision 1696322)
+++ modules/session/mod_session.c	(working copy)
@@ -177,6 +177,7 @@ 
 {
     if (z) {
         apr_time_t now = apr_time_now();
+        apr_time_t initialExpiry = z->expiry;
         int rv = 0;
 
         session_dir_conf *dconf = ap_get_module_config(r->per_dir_config,
@@ -207,6 +208,18 @@ 
             z->expiry = now + z->maxage * APR_USEC_PER_SEC;
         } 
 
+        /* don't save if the only change is the expiry by a small amount */
+        if (!z->dirty && dconf->expiry_update_time
+            && (z->expiry - initialExpiry
+                < dconf->expiry_update_time * APR_USEC_PER_SEC)) {
+            return APR_SUCCESS;
+        }
+
+        /* also don't save sessions that didn't change at all */
+        if (!z->dirty && !z->maxage) {
+            return APR_SUCCESS;
+        }
+
         /* encode the session */
         rv = ap_run_session_encode(r, z);
         if (OK != rv) {
@@ -551,6 +564,9 @@ 
     new->env_set = add->env_set || base->env_set;
     new->includes = apr_array_append(p, base->includes, add->includes);
     new->excludes = apr_array_append(p, base->excludes, add->excludes);
+    new->expiry_update_time = (add->expiry_update_set == 0) ?
+        base->expiry_update_time : add->expiry_update_time;
+    new->expiry_update_set = add->expiry_update_set || base->expiry_update_set;
 
     return new;
 }
@@ -620,7 +636,18 @@ 
     return NULL;
 }
 
+static const char *
+     set_session_expiry_update(cmd_parms * parms, void *dconf, const char *arg)
+{
+    session_dir_conf *conf = dconf;
 
+    conf->expiry_update_time = atol(arg);
+    conf->expiry_update_set = 1;
+
+    return NULL;
+}
+
+
 static const command_rec session_cmds[] =
 {
     AP_INIT_FLAG("Session", set_session_enable, NULL, RSRC_CONF|OR_AUTHCFG,
@@ -635,6 +662,8 @@ 
                   "URL prefixes to include in the session. Defaults to all URLs"),
     AP_INIT_TAKE1("SessionExclude", add_session_exclude, NULL, RSRC_CONF|OR_AUTHCFG,
                   "URL prefixes to exclude from the session. Defaults to no URLs"),
+    AP_INIT_TAKE1("SessionExpiryUpdateInterval", set_session_expiry_update, NULL, RSRC_CONF|OR_AUTHCFG,
+                  "length of time for which a session's expiry time may change without having to be rewritten. Zero to disable"),
     {NULL}
 };
 
--- modules/session/mod_session.h	(revision 1696322)
+++ modules/session/mod_session.h	(working copy)
@@ -115,6 +115,9 @@ 
                                    * URLs included if empty */
     apr_array_header_t *excludes; /* URL prefixes to be excluded. No
                                    * URLs excluded if empty */
+    long expiry_update_time;      /* seconds the session expiry may change and
+                                   * not have to be rewritten */
+    int expiry_update_set;
 } session_dir_conf;
 
 /**
--- modules/session/mod_session_dbd.c	(revision 1696322)
+++ modules/session/mod_session_dbd.c	(working copy)
@@ -245,6 +245,9 @@ 
     /* put the session in the notes so we don't have to parse it again */
     apr_table_setn(m->notes, note, (char *)zz);
 
+    /* don't cache pages with a session */
+    apr_table_addn(r->headers_out, "Cache-Control", "no-cache");
+
     return OK;
 
 }
@@ -409,9 +412,6 @@ 
     if (conf->name_set || conf->name2_set) {
         char *oldkey = NULL, *newkey = NULL;
 
-        /* don't cache pages with a session */
-        apr_table_addn(r->headers_out, "Cache-Control", "no-cache");
-
         /* if the session is new or changed, make a new session ID */
         if (z->uuid) {
             oldkey = apr_pcalloc(r->pool, APR_UUID_FORMATTED_LENGTH + 1);
--- modules/session/mod_session_cookie.c	(revision 1696322)
+++ modules/session/mod_session_cookie.c	(working copy)
@@ -60,9 +60,6 @@ 
     session_cookie_dir_conf *conf = ap_get_module_config(r->per_dir_config,
                                                     &session_cookie_module);
 
-    /* don't cache auth protected pages */
-    apr_table_addn(r->headers_out, "Cache-Control", "no-cache");
-
     /* create RFC2109 compliant cookie */
     if (conf->name_set) {
         if (z->encoded && z->encoded[0]) {
@@ -162,6 +159,9 @@ 
     /* put the session in the notes so we don't have to parse it again */
     apr_table_setn(m->notes, note, (char *)zz);
 
+    /* don't cache auth protected pages */
+    apr_table_addn(r->headers_out, "Cache-Control", "no-cache");
+
     return OK;
 
 }