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</div><hr /><div id="mongo.connecting.rs" class="section">
<h2 class="title">Replica Sets</h2>
<p class="para">
To connect to a replica set, specify one or more members of the set and use
the <em>"replicaSet"</em> option. Multiple servers may be delimited
by a comma.
</p>
<div class="example" id="mongo.connecting.rs-example">
<p><strong>Example #1 ReplicaSet seedlist</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">// Using multiple servers as the seed list (prefered)<br /></span><span style="color: #0000BB">$m </span><span style="color: #007700">= new </span><span style="color: #0000BB">MongoClient</span><span style="color: #007700">(</span><span style="color: #DD0000">"mongodb://rs1.example.com:27017,rs2.example.com:27017/?replicaSet=myReplSetName"</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">// Using one server as the seed list<br /></span><span style="color: #0000BB">$m </span><span style="color: #007700">= new </span><span style="color: #0000BB">MongoClient</span><span style="color: #007700">(</span><span style="color: #DD0000">"mongodb://rs1.example.com:27017"</span><span style="color: #007700">, array(</span><span style="color: #DD0000">"replicaSet" </span><span style="color: #007700">=> </span><span style="color: #DD0000">"myReplSetName"</span><span style="color: #007700">));<br /><br /></span><span style="color: #FF8000">// Using multiple servers as the seed list<br /></span><span style="color: #0000BB">$m </span><span style="color: #007700">= new </span><span style="color: #0000BB">MongoClient</span><span style="color: #007700">(</span><span style="color: #DD0000">"mongodb://rs1.example.com:27017,rs2.example.com:27017"</span><span style="color: #007700">, array(</span><span style="color: #DD0000">"replicaSet" </span><span style="color: #007700">=> </span><span style="color: #DD0000">"myReplSetName"</span><span style="color: #007700">));<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
<p class="para">
The PHP driver will query the database server(s) listed to determine the
primary. So long as it can connect to at least one host listed and find a
primary, the connection will succeed. If it cannot make a connection to any
servers listed or cannot find a primary, a
<a href="class.mongoconnectionexception.html" class="classname">MongoConnectionException</a> will be thrown.
</p>
<div class="tip"><strong class="tip">Tip</strong>
<p class="para">
You should always provide a seedlist with more than one member of the
ReplicaSet. For highest availability you should seed with at least one
server from each of your datacenters.
</p>
</div>
<div class="warning"><strong class="warning">Warning</strong>
<p class="para">
The host names that you specify here <em class="emphasis">must</em> match the
names as given in the replica set configuration because the driver uses the
name as specified in the replica set configuration as identifier in its
internal mapping. Specifying (for example) the IP address instead of the
configured host name makes that the driver keeps a connection for both the
host name and its accompanying IP address.
</p>
</div>
<div class="warning"><strong class="warning">Warning</strong>
<p class="para">
The driver does <em class="emphasis">not</em> support connecting to different
replica sets with the same name. This extends beyond one script so make
sure to have separate names for each of your replica sets. That also means
that you can <em class="emphasis">not</em> do this:
</p>
<div class="example" id="mongo.connecting.rs-example-wrong-replset">
<p><strong>Example #2 Wrong replica set name duplication</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$m </span><span style="color: #007700">= new </span><span style="color: #0000BB">MongoClient</span><span style="color: #007700">(</span><span style="color: #DD0000">"mongodb://devserver1,devserver2,devserver3/?replicaSet=repset"</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$m </span><span style="color: #007700">= new </span><span style="color: #0000BB">MongoClient</span><span style="color: #007700">(</span><span style="color: #DD0000">"mongodb://prodserver1,prodserver2,prodserver3/?replicaSet=repset"</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
<p class="para">
Instead, you need to have two different names for your replica sets:
</p>
<div class="example" id="mongo.connecting.rs-example-correct-replset">
<p><strong>Example #3 Correct use of two replica set names</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$m </span><span style="color: #007700">= new </span><span style="color: #0000BB">MongoClient</span><span style="color: #007700">(</span><span style="color: #DD0000">"mongodb://devserver1,devserver2,devserver3/?replicaSet=devset"</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$m </span><span style="color: #007700">= new </span><span style="color: #0000BB">MongoClient</span><span style="color: #007700">(</span><span style="color: #DD0000">"mongodb://prodserver1,prodserver2,prodserver3/?replicaSet=prodset"</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</div>
<p class="para">
If the primary becomes unavailable, an election will take place and a
secondary will be promoted to the role of primary (unless a majority vote
cannot be established). During this time
(<a href="http://docs.mongodb.org/manual/faq/replica-sets/#how-long-does-replica-set-failover-take" class="link external">» 20-60 seconds</a>), the
connection will not be able to perform any write operations and attempts to
do so will result in an exception. Connections to secondaries will still be
able to perform reads.
</p>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
The default <a href="mongo.readpreferences.html" class="link">Read Preference</a>
is to only read from the primary. During the election process there is no
primary, and all read will therefore fail.
</p>
<p class="para">
It is recommended to use
<strong><code>MongoClient::RP_PRIMARY_PREFERRED</code></strong> Read Preference for
applications that require high availability for reads, as reads will only
be executed on the secondaries when there simply isn't a primary
available.
</p>
</p></blockquote>
<p class="para">
Once a primary is elected, attempting to perform a read or write will allow
the driver to detect the new primary. The driver will make this its primary
database connection and continue operating normally.
</p>
<p class="para">
The health and state of a secondary is checked every 5 seconds
(configurable with
<a href="mongo.configuration.html#ini.mongo.ping-interval" class="link">mongo.ping_interval</a>)
or when the next operation occurs after 5 seconds. It will also recheck
the configuration when the driver has a problem reaching a server.
</p>
<p class="para">
Replica set failovers are checked every 60 seconds (configurable with
<a href="mongo.configuration.html#ini.mongo.is-master-interval" class="link">mongo.is_master_interval</a>),
and whenever a write operation fails when using acknowledged writes.
</p>
<div class="caution"><strong class="caution">Caution</strong>
<p class="para">
Secondaries may be behind the primary in operations, so
your application must be able to handle out-of-date data when using
Read Preferences other then <strong><code>MongoClient::RP_PRIMARY</code></strong>.
</p>
</div>
<p class="para">
For more information on replica sets, see the
<a href="http://docs.mongodb.org/manual/replication/" class="link external">» core documentation</a>.
</p>
<div class="simplesect">
<h3 class="title">See Also</h3>
<ul class="simplelist">
<li class="member"><a href="mongo.readpreferences.html" class="xref">Read Preferences</a></li>
<li class="member"><a href="mongo.writeconcerns.html" class="xref">Write Concerns</a></li>
</ul>
</div>
<div class="simplesect">
<h3 class="title">Changelog</h3>
<table class="doctable informaltable">
<thead>
<tr>
<th>Version</th>
<th>Description</th>
</tr>
</thead>
<tbody class="tbody">
<tr>
<td>1.0.9</td>
<td>
Added support for connecting to ReplicaSet and automatic failover.
</td>
</tr>
</tbody>
</table>
</div>
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