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Jan 29, 2018
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sampleRate is global #3206

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15 changes: 10 additions & 5 deletions source/tutorial/manage-the-database-profiler.txt
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Expand Up @@ -122,8 +122,8 @@ Profile a Random Sample of Slow Operations

.. versionadded:: 3.6

To profile only a randomly sampled subset of all *slow* operations on a
specific database, specify the desired sample rate in one of the following ways:
To profile only a randomly sampled subset of all *slow* operations, specify the
desired sample rate in one of the following ways:

- Set the value of ``sampleRate`` using the :dbcommand:`profile` command
or :method:`db.setProfilingLevel()` shell helper method.
Expand All @@ -135,9 +135,9 @@ specific database, specify the desired sample rate in one of the following ways:
:ref:`configuration file <configuration-options>`.

By default, ``sampleRate`` is set to ``1.0``, meaning all *slow*
operations are profiled. Databases with a ``sampleRate`` between 0 and 1
will only profile a randomly sampled percentage of *slow* operations
according to ``sampleRate``.
operations are profiled. When ``sampleRate`` is set between 0 and 1
databases with profiling level ``1`` will only profile a randomly sampled
percentage of *slow* operations according to ``sampleRate``.

For example, the following method sets the profiling level for the
current database to ``1`` and sets the profiler to sample 42% of all *slow* operations:
Expand All @@ -146,6 +146,11 @@ current database to ``1`` and sets the profiler to sample 42% of all *slow* oper

db.setProfilingLevel(1, { sampleRate: 0.42 })

.. important::
The sample rate value applies to all databases in a
:binary:`~bin.mongod` instance. It is used by both the database profiler
and the system log

.. important::
.. include:: /includes/fact-log-slow-queries.rst

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