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DOCSP-50588 Find Slow Queries with currentOp (#12445)
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‎content/manual/upcoming/source/administration/query.txt‎

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- :ref:`manual-find-slow-queries-with-database-profiler`
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- :ref:`manual-monitor-slow-queries`
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- :ref:`manual-explain-slow-queries`
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Solutions
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- Whether the query uses an index
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For more information, see :ref:`profiler`.
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.. note::
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The database profiler is not available on :program:`mongos`.
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If you need to find slow queries on a sharded cluster, see
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:ref:`manual-qp-currentOp`.
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.. _manual-qp-currentOp:
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Monitor Current Operations
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~~~~~~~~~~~~~~~~~~~~~~~~~~
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The :pipeline:`$currentOp` aggregation stage returns information
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on operations currently running on a MongoDB server or cluster.
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``$currentOp`` can help you identify performance issues, such as:
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- How long the query takes to run
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- Whether the query is waiting on a lock
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- Whether the query uses an index
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For more information, see :ref:`manual-monitor-slow-queries`.
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.. _manual-qp-explain:
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Explain
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~~~~~~~
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‎content/manual/upcoming/source/includes/fact-profiler-use.rst‎

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This task runs the :method:`~db.collection.explain` method on a
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sample query in an attempt to identify performance issues. In
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practice, it may be difficult to run ``explain()`` on every
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query your application runs.
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To narrow the list of queries sent by your application to only
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those that are slow, you can use a profiler:
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.. list-table::
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:header-rows: 1

‎content/manual/upcoming/source/tutorial/evaluate-operation-performance.txt‎

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Explain Results </reference/explain-results>
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Database Profiler </tutorial/manage-the-database-profiler>
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Monitor Slow Queries </tutorial/monitor-slow-queries>
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Block Slow Queries </tutorial/operation-rejection-filters>

‎content/manual/upcoming/source/tutorial/explain-slow-queries.txt‎

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Profilers
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~~~~~~~~~
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This task runs the :method:`~db.collection.explain` method on a
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sample query in an attempt to identify performance issues. In
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practice, it may be difficult to run ``explain()`` on every
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query your application runs.
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To narrow the list of queries to analyze to only those that are
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slow, you can use a profiler:
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.. include:: /includes/fact-profiler-use
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Steps

‎content/manual/upcoming/source/tutorial/find-slow-queries-with-database-profiler.txt‎

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- If ``keysExamined`` is high and ``docsExamined`` is low,
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it indicates effective index use.
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.. step:: Explain the query.
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If the database profiler identifies a query that requires
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further investigation, use the
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:method:`~db.collection.explain` method to analyze the
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query plan and execution statistics.
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For details, see :ref:`manual-explain-slow-queries`.
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.. step:: Disable the database profiler.
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To ensure that the database profiler does not further

‎content/manual/upcoming/source/tutorial/monitor-slow-queries.txt‎

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.. meta::
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:description: Manage the database profiler to collect detailed information on database commands, affecting performance and disk use when enabled.
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.. _manual-monitor-slow-queries:
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====================
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Monitor Slow Queries
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====================
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.. contents:: On this page
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:local:
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:backlinks: none
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:depth: 1
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:class: singlecol
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The :pipeline:`$currentOp` aggregation stage provides
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information on all operations currently running on MongoDB. If
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your application is experiencing performance issues, you can
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build an aggregation pipeline around this stage to monitor for
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slow queries and similar issues.
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About This Task
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---------------
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Database Profilers
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~~~~~~~~~~~~~~~~~~
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This task uses :pipeline:`$currentOp` to identify slow queries
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currently running on your application. To find all slow queries
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within a specified period, consider using a profiler.
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.. include:: /includes/fact-profiler-use
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Explain Queries
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~~~~~~~~~~~~~~~
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This task identifies queries with performance issues. If you
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already know which queries have performance issues, see
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:ref:`manual-explain-slow-queries` to troubleshoot them.
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Steps
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-----
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.. procedure::
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:style: normal
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.. step:: Retrieve current operations.
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Use the :pipeline:`$currentOp` aggregation stage to
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retrieve current operations from MongoDB:
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.. io-code-block::
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.. input::
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:language: javascript
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db.getSiblingDB("admin").aggregate( [
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{ $currentOp: { allUsers: true } },
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{ $match: { secs_running: { $gt: 2 } } },
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{ $sort: { secs_running: 1 } }
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] )
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.. output::
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:language: javascript
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[
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{
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"opid": "12345",
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"secs_running": 5,
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"active": true,
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"ns": "sample_mflix.movies",
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"command": {
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"find": "movies",
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"filter": { "title": { "$regex": "The" } }
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},
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"planSummary": "COLLSCAN",
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"locks": { ... },
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"client": "203.0.113.25:43210"
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}
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]
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This aggregation pipeline retrieves all current operations
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in the cluster. The :pipeline:`$match` aggregation stage
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then filters the operations to those that have been
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running for more than two seconds. This allows you to
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filter queries that run within a specified period. Adjust
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the value to match your application and database needs.
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The :pipeline:`$sort` stage sorts the results in
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ascending operation time order.
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.. step:: Check for activity.
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View the :data:`currentOp.active` field. If ``currentOp.active`` is
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``true``, MongoDB indicates that the operation is currently
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running.
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To stop a long running operation, use the
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:method:`db.killOp` method to stop the given
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:data:`~currentOp.opid`.
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.. step:: Check for locks.
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View the :data:`currentOp.waitingForLock` field. If ``currentOp.waitingForLock`` is
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``true``, another operation running on the server or cluster is blocking the query.
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To stop a blocked operation, use the :method:`db.killOp`
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method to stop the given :data:`~currentOp.opid`.
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.. step:: Check the plan summary.
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Check the value in the :data:`currentOp.planSummary`
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field.
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``IXSCAN``
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Indicates the query performed an index scan.
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``COLLSCAN``
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Indicates the query performed a full collection scan.
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To correct this, :ref:`manual-create-an-index`.
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.. step:: Explain the query.
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If the :pipeline:`$currentOp` aggregation stage returns a
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query that requires further investigation, use the
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:method:`~db.collection.explain` method to analyze the
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query plan and execution statistics.
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For details, see :ref:`manual-explain-slow-queries`.
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Learn More
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----------
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- :ref:`query-performance`
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- :ref:`profiler`
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- :ref:`manual-find-slow-queries-with-database-profiler`
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- :ref:`manual-explain-slow-queries`

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