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</div><hr /><div id="mongodb.connection-handling" class="article">
<h1>Connection handling and persistence</h1>
<blockquote class="note"><p><strong class="note">Note</strong>:
<span class="simpara">
On Unix platforms, the MongoDB driver is sensitive to scripts that use the
fork() system call without also calling exec(). Users are advised not to
re-use <a href="class.mongodb-driver-manager.html" class="classname">MongoDB\Driver\Manager</a> instances in a forked
child process.
</span>
</p></blockquote>
<div class="section">
<h2 class="title">Connection and topology persistence (PHP version since 1.2.0)</h2>
<p class="para">
All versions of the driver since 1.2.0 persist the
<a href="https://github.com/mongodb/mongo-c-driver" class="link external">» libmongoc</a> client object in
the PHP worker process, which allows it to re-use database connections,
authentication states, <em class="emphasis">and</em> topology information across
multiple requests.
</p>
<p class="para">
When <span class="methodname"><a href="mongodb-driver-manager.construct.html" class="methodname">MongoDB\Driver\Manager::__construct()</a></span> is
invoked, a hash is created from its arguments (i.e. URI string and array
options). The driver will attempt to find a previously persisted
<a href="https://github.com/mongodb/mongo-c-driver" class="link external">» libmongoc</a> client object for
that hash. If an existing client cannot be found for the hash, a new client
will be created (and persisted for future use).
</p>
<p class="para">
Each client contains its own database connections and a view of the server
topology (e.g. standalone, replica set, shard cluster). By persisting the
client between PHP requests, the driver is able to re-use established
database connections and remove the need for
<a href="https://github.com/mongodb/specifications/blob/master/source/server-discovery-and-monitoring/server-discovery-and-monitoring.rst" class="link external">» discovering the server topology</a>
on each request.
</p>
<p class="para">
Consider the following example:
</p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /><br />$managers </span><span style="color: #007700">= [<br /> new </span><span style="color: #0000BB">MongoDB</span><span style="color: #007700">\</span><span style="color: #0000BB">Driver</span><span style="color: #007700">\</span><span style="color: #0000BB">Manager</span><span style="color: #007700">(</span><span style="color: #DD0000">'mongodb://127.0.0.1'</span><span style="color: #007700">),<br /> new </span><span style="color: #0000BB">MongoDB</span><span style="color: #007700">\</span><span style="color: #0000BB">Driver</span><span style="color: #007700">\</span><span style="color: #0000BB">Manager</span><span style="color: #007700">(</span><span style="color: #DD0000">'mongodb://127.0.0.1'</span><span style="color: #007700">),<br /> new </span><span style="color: #0000BB">MongoDB</span><span style="color: #007700">\</span><span style="color: #0000BB">Driver</span><span style="color: #007700">\</span><span style="color: #0000BB">Manager</span><span style="color: #007700">(</span><span style="color: #DD0000">'mongodb://127.0.0.1:27017'</span><span style="color: #007700">),<br /> new </span><span style="color: #0000BB">MongoDB</span><span style="color: #007700">\</span><span style="color: #0000BB">Driver</span><span style="color: #007700">\</span><span style="color: #0000BB">Manager</span><span style="color: #007700">(</span><span style="color: #DD0000">'mongodb://rs1.example.com,rs2.example.com/'</span><span style="color: #007700">, [</span><span style="color: #DD0000">'replicaSet' </span><span style="color: #007700">=> </span><span style="color: #DD0000">'myReplicaSet'</span><span style="color: #007700">]),<br />];<br /><br />foreach (</span><span style="color: #0000BB">$managers </span><span style="color: #007700">as </span><span style="color: #0000BB">$manager</span><span style="color: #007700">) {<br /> </span><span style="color: #0000BB">$manager</span><span style="color: #007700">-></span><span style="color: #0000BB">executeCommand</span><span style="color: #007700">(</span><span style="color: #DD0000">'test'</span><span style="color: #007700">, new </span><span style="color: #0000BB">MongoDB</span><span style="color: #007700">\</span><span style="color: #0000BB">Driver</span><span style="color: #007700">\</span><span style="color: #0000BB">Command</span><span style="color: #007700">([</span><span style="color: #DD0000">'ping' </span><span style="color: #007700">=> </span><span style="color: #0000BB">1</span><span style="color: #007700">]));<br />}<br /><br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
<p class="para">
The first two Manager objects will share the same
<a href="https://github.com/mongodb/mongo-c-driver" class="link external">» libmongoc</a> client since
their constructor arguments are identical. The third and fourth objects will
each use their own client. In total, three clients will be created and the
PHP worker executing this script will open two connections to
<em>127.0.0.1</em> and one connection to each of
<em>rs1.example.com</em> and <em>rs2.example.com</em>.
If the driver discovers additional members of the replica set after issuing
<em>isMaster</em> commands, it will open additional connections to
those servers as well.
</p>
<p class="para">
If the same worker executes the script again in a second request, the three
clients will be re-used and no new connections should be made. Depending on
how long ago the previous request was served, the driver may need to issue
additional <em>isMaster</em> commands to update its view of the
topologies.
</p>
</div>
<div class="section">
<h2 class="title">Socket persistence (PHP versions before 1.2.0)</h2>
<p class="para">
Versions of the PHP driver before 1.2.0 utilize PHP's Streams API for
database connections, using an API within
<a href="https://github.com/mongodb/mongo-c-driver" class="link external">» libmongoc</a> to designate
custom handlers for socket communication; however, a new libmongoc client is
created for each <a href="class.mongodb-driver-manager.html" class="classname">MongoDB\Driver\Manager</a>. As a result,
the driver persists individual database connections but not authentication
state or topology information. This means that the driver needs to issue
commands at the start of each request to authenticate and
<a href="https://github.com/mongodb/specifications/blob/master/source/server-discovery-and-monitoring/server-discovery-and-monitoring.rst" class="link external">» discover the server topology</a>.
</p>
<p class="para">
Database connections are persisted by a hash derived from the server's
host, port, and the URI string used to construct the
<a href="class.mongodb-driver-manager.html" class="classname">MongoDB\Driver\Manager</a>. The constructor's array
options are not included in this hash.
</p>
<blockquote class="note"><p><strong class="note">Note</strong>:
<span class="simpara">
Versions of the driver >= 1.1.8 and < 1.2.0 do not persist sockets
for SSL connections. See
<a href="https://jira.mongodb.org/browse/PHPC-720" class="link external">» PHPC-720</a> for
additional information.
</span>
</p></blockquote>
<p class="para">
Despite its shortcomings with persisting SSL connections when and topology
information, this version of the driver supports all
<a href="context.ssl.html" class="link">SSL context options</a> since it uses
PHP's Streams API.
</p>
</div>
</div>
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