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DOCSP-48388 break up faq #1048
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DOCSP-48388 break up faq #1048
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@@ -91,9 +91,9 @@ string, see :manual:`Connection Strings </reference/connection-string/>` in the | |||||||||
* - **connectTimeoutMS** | ||||||||||
- non-negative integer | ||||||||||
- ``30000`` | ||||||||||
- Specifies the amount of time, in milliseconds, to wait to establish a single TCP | ||||||||||
- Specifies the amount of time in milliseconds to wait to establish a single TCP | ||||||||||
socket connection to the server before raising an error. Specifying | ||||||||||
``0`` disables the connection timeout. | ||||||||||
``0`` means your application will use the operating system's default socket timeout value. | ||||||||||
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* - **directConnection** | ||||||||||
- boolean | ||||||||||
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@@ -255,8 +255,9 @@ string, see :manual:`Connection Strings </reference/connection-string/>` in the | |||||||||
* - **socketTimeoutMS** | ||||||||||
- non-negative integer | ||||||||||
- ``0`` | ||||||||||
- Specifies the amount of time, in milliseconds, spent attempting to send or receive on a | ||||||||||
socket before timing out. Specifying ``0`` means no timeout. | ||||||||||
- Specifies the amount of time in milliseconds spent attempting to send or receive | ||||||||||
on a socket before timing out. Specifying ``0`` means your application will use the | ||||||||||
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operating system's default socket timeout value. | ||||||||||
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* - **srvMaxHosts** | ||||||||||
- non-negative integer | ||||||||||
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@@ -343,6 +344,114 @@ string, see :manual:`Connection Strings </reference/connection-string/>` in the | |||||||||
no compression, ``1`` signifies the fastest speed, and ``9`` signifies | ||||||||||
the best compression. See :ref:`node-network-compression` for more information. | ||||||||||
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Connection Time Out Options | ||||||||||
--------------------------- | ||||||||||
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.. list-table:: | ||||||||||
:widths: 22 78 | ||||||||||
:header-rows: 1 | ||||||||||
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* - Setting | ||||||||||
- Description | ||||||||||
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* - **connectTimeoutMS** | ||||||||||
- ``connectTimeoutMS`` is a :ref:`connection option | ||||||||||
<node-connection-options>` that sets the time, in milliseconds, | ||||||||||
for an individual connection from your connection pool to | ||||||||||
establish a TCP connection to the {+mdb-server+} before | ||||||||||
timing out. To modify the allowed time for | ||||||||||
`MongoClient.connect <{+api+}/classes/MongoClient.html#connect>`__ to establish a | ||||||||||
connection to a {+mdb-server+}, use the ``serverSelectionTimeoutMS`` option instead. | ||||||||||
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**Default:** 30000 | ||||||||||
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* - **socketTimeoutMS** | ||||||||||
- ``socketTimeoutMS`` specifies the amount of time the driver waits | ||||||||||
for an inactive socket before closing it. The default value is to | ||||||||||
never time out the socket. This option applies only to sockets that | ||||||||||
have already been connected. | ||||||||||
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* - **maxTimeMS** | ||||||||||
- `maxTimeMS <{+api+}/classes/FindCursor.html#maxTimeMS>`__ | ||||||||||
specifies the maximum amount of time that the server | ||||||||||
waits for an operation to complete after it has reached the | ||||||||||
server. If an operation runs over the specified time limit, it | ||||||||||
returns a timeout error. You can pass ``maxTimeMS`` only to an | ||||||||||
individual operation or to a cursor. | ||||||||||
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To specify the optional settings for your ``MongoClient``, declare one or | ||||||||||
more available settings in the ``options`` object of the constructor as | ||||||||||
follows: | ||||||||||
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.. code-block:: javascript | ||||||||||
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const client = new MongoClient(uri, { | ||||||||||
connectTimeoutMS: <integer value>, | ||||||||||
socketTimeoutMS: <integer value> | ||||||||||
}); | ||||||||||
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To see all the available settings, see the | ||||||||||
`MongoClientOptions <{+api+}/interfaces/MongoClientOptions.html>`__ | ||||||||||
API Documentation. | ||||||||||
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To specify ``maxTimeMS``, chain the ``maxTimeMS()`` method with a | ||||||||||
timeout specification to an operation that returns a ``Cursor``: | ||||||||||
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.. code-block:: javascript | ||||||||||
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const cursor = myColl.find({}).maxTimeMS(50); | ||||||||||
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Close Sockets After Connection | ||||||||||
------------------------------ | ||||||||||
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If you experience unexpected network behavior or if a MongoDB process | ||||||||||
fails with an error, you may not receive confirmation that the | ||||||||||
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driver correctly closed the corresponding socket. | ||||||||||
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To make sure that the driver correctly closes the socket in these cases, | ||||||||||
set the ``socketTimeoutMS`` option. When a MongoDB process times out, the driver | ||||||||||
will close the socket. We recommend that you select a value | ||||||||||
for ``socketTimeoutMS`` that is two to three times longer than the | ||||||||||
expected duration of the slowest operation that your application executes. | ||||||||||
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Prevent Long-Running Operations From Slowing Down the Server | ||||||||||
------------------------------------------------------------ | ||||||||||
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You can prevent long-running operations from slowing down the server by | ||||||||||
specifying a timeout value. You can chain the ``maxTimeMS()`` method to | ||||||||||
an operation that returns a ``Cursor`` to set a timeout on a specific action. | ||||||||||
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The following example shows how you can chain the ``maxTimeMS()`` method | ||||||||||
to an operation that returns a ``Cursor``: | ||||||||||
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.. literalinclude:: /code-snippets/faq/maxTimeMS-example.js | ||||||||||
:language: javascript | ||||||||||
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.. _node-faq-keepalive: | ||||||||||
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keepAlive Connection Option | ||||||||||
--------------------------- | ||||||||||
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The ``keepAlive`` connection option specifies whether to enable | ||||||||||
:wikipedia:`Transmission Control Protocol (TCP) keepalives | ||||||||||
<Keepalive#TCP_keepalive>` on a TCP socket. If you enable keepalives, | ||||||||||
the driver checks whether the connection is active by sending periodic pings | ||||||||||
to your MongoDB deployment. This functionality only works if your | ||||||||||
operating system supports the ``SO_KEEPALIVE`` socket option. | ||||||||||
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The ``keepAliveInitialDelay`` option specifies the number of | ||||||||||
milliseconds that the driver waits before initiating a keepalive. | ||||||||||
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The 5.3 driver version release deprecated these options. Starting in | ||||||||||
version 6.0 of the driver, the ``keepAlive`` option is permanently set | ||||||||||
to ``true``, and the ``keepAliveInitialDelay`` is set to 300000 | ||||||||||
milliseconds (300 seconds). | ||||||||||
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.. warning:: | ||||||||||
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If your firewall ignores or drops the keepalive messages, you might | ||||||||||
not be able to identify dropped connections. | ||||||||||
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Additional Information | ||||||||||
---------------------- | ||||||||||
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@@ -27,4 +27,115 @@ gets a connection from the pool, performs operations, and returns the connection | |
to the pool for reuse. | ||
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Connection pools help reduce application latency and the number of times new connections | ||
are created by {+driver-short+}. | ||
are created by {+driver-short+}. | ||
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.. _node-faq-connection-pool: | ||
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Connection Pool Overview | ||
Comment on lines
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There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. This seems out of scope for the ticket this PR applies to, but I think it would be worth creating a ticket to clean this page up a bit. This Connection Pool Overview section is very long and would probably benefit from being broken up into sections now that it's in its own page instead of an FAQ. There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Good idea, made a ticket here: https://jira.mongodb.org/browse/DOCSP-48683 |
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------------------------- | ||
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Every ``MongoClient`` instance has a built-in connection pool for each server | ||
in your MongoDB topology. Connection pools open sockets on demand to | ||
support concurrent requests to MongoDB in your application. | ||
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The maximum size of each connection pool is set by the ``maxPoolSize`` option, which | ||
defaults to ``100``. If the number of in-use connections to a server reaches | ||
the value of ``maxPoolSize``, the next request to that server will wait | ||
until a connection becomes available. | ||
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In addition to the sockets needed to support your application's requests, | ||
each ``MongoClient`` instance opens two more sockets per server | ||
in your MongoDB topology for monitoring the server's state. | ||
For example, a client connected to a three-node replica set opens six | ||
monitoring sockets. If the application uses the default setting for | ||
``maxPoolSize`` and only queries the primary (default) node, then | ||
there can be at most ``106`` total connections in the connection pool. If the | ||
application uses a :ref:`read preference <read-preference>` to query the | ||
secondary nodes, those connection pools grow and there can be | ||
``306`` total connections. | ||
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To support high numbers of concurrent MongoDB requests | ||
within one process, you can increase ``maxPoolSize``. | ||
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Connection pools are rate-limited. The ``maxConnecting`` option | ||
determines the number of connections that the pool can create in | ||
parallel at any time. For example, if the value of ``maxConnecting`` is | ||
``2``, the third request that attempts to concurrently check out a | ||
connection succeeds only when one the following cases occurs: | ||
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- The connection pool finishes creating a connection and there are fewer | ||
than ``maxPoolSize`` connections in the pool. | ||
- An existing connection is checked back into the pool. | ||
- The driver's ability to reuse existing connections improves due to | ||
rate-limits on connection creation. | ||
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You can set the minimum number of concurrent connections to | ||
each server with the ``minPoolSize`` option, which defaults to ``0``. | ||
The driver initializes the connection pool with this number of sockets. If | ||
sockets are closed, causing the total number | ||
of sockets (both in use and idle) to drop below the minimum, more | ||
sockets are opened until the minimum is reached. | ||
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You can set the maximum number of milliseconds that a connection can | ||
remain idle in the pool by setting the ``maxIdleTimeMS`` option. | ||
Once a connection has been idle for ``maxIdleTimeMS``, the connection | ||
pool removes and replaces it. This option defaults to ``0`` (no limit). | ||
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The following default configuration for a ``MongoClient`` works for most | ||
applications: | ||
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.. code-block:: js | ||
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const client = new MongoClient("<connection string>"); | ||
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``MongoClient`` supports multiple concurrent requests. For each process, | ||
create a client and reuse it for all operations in a process. This | ||
practice is more efficient than creating a client for each request. | ||
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The driver does not limit the number of requests that | ||
can wait for sockets to become available, and it is the application's | ||
responsibility to limit the size of its pool to bound queuing | ||
during a load spike. Requests wait for the amount of time specified in | ||
the ``waitQueueTimeoutMS`` option, which defaults to ``0`` (no limit). | ||
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A request that waits more than the length of time defined by | ||
``waitQueueTimeoutMS`` for a socket raises a connection error. Use this | ||
option if it is more important to bound the duration of operations | ||
during a load spike than it is to complete every operation. | ||
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When ``MongoClient.close()`` is called by any request, the driver | ||
closes all idle sockets and closes all sockets that are in | ||
use as they are returned to the pool. Calling ``MongoClient.close()`` | ||
closes only inactive sockets and does not directly terminate | ||
any ongoing operations. The driver closes any in-use sockets only when | ||
the associated operations complete. However, the ``MongoClient.close()`` | ||
method does close existing sessions and transactions, which might indirectly | ||
affect the behavior of ongoing operations and open cursors. | ||
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Avoid Socket Timeouts | ||
--------------------- | ||
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Having a large connection pool does not always reduce reconnection | ||
requests. Consider the following example: | ||
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An application has a connection pool size of 5 sockets and has the | ||
``socketTimeoutMS`` option set to 5000 milliseconds. Operations occur, | ||
on average, every 3000 milliseconds, and reconnection requests are | ||
frequent. Each socket times out after 5000 milliseconds, which means | ||
that all sockets must do something during those 5000 milliseconds to | ||
avoid closing. | ||
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One message every 3000 milliseconds is not enough to keep the sockets | ||
active, so several of the sockets will time out after 5000 milliseconds. | ||
To avoid excessive socket timeouts, reduce the number of connections | ||
that the driver can maintain in the connection pool by specifying the | ||
``maxPoolSize`` option. | ||
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To specify the optional ``maxPoolSize`` setting for your ``MongoClient``, declare | ||
it in the ``options`` object of the constructor as follows: | ||
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.. code-block:: javascript | ||
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const client = new MongoClient(uri, { | ||
maxPoolSize: <integer value>, | ||
}); |
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