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parallelCollectionScan.txt
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parallelCollectionScan.txt
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======================
parallelCollectionScan
======================
.. default-domain:: mongodb
.. contents:: On this page
:local:
:backlinks: none
:depth: 1
:class: singlecol
.. dbcommand:: parallelCollectionScan
.. versionadded:: 2.6
Allows applications to use multiple parallel cursors when reading
all the documents from a collection, thereby increasing throughput.
The :dbcommand:`parallelCollectionScan` command returns a document
that contains an array of cursor information.
Each cursor provides access to the return of a partial set of documents
from a collection. Iterating each cursor returns every document in the
collection. Cursors do not contain the results of the database command.
The result of the database command identifies the cursors, but does not
contain or constitute the cursors.
The server may return fewer cursors than requested.
The command has the following syntax:
.. code-block:: javascript
{
parallelCollectionScan: "<collection>",
numCursors: <integer>
}
The :dbcommand:`parallelCollectionScan` command takes the following
fields:
.. list-table::
:header-rows: 1
:widths: 20 20 80
* - Field
- Type
- Description
* - ``parallelCollectionScan``
- string
- The name of the collection.
* - ``numCursors``
- integer
- The maximum number of cursors to return. Must be between 1 and 10000, inclusive.
:dbcommand:`parallelCollectionScan` is only available for :binary:`~bin.mongod`,
and it cannot operate on a sharded cluster.
Output
------
The :dbcommand:`parallelCollectionScan` command returns a document
containing the array of cursor information:
.. code-block:: javascript
{
"cursors" : [
{
"cursor" : {
"firstBatch" : [ ],
"ns" : "<database name>.<collection name>",
"id" : NumberLong("155949257847")
},
"ok" : true
}
],
"ok" : 1
}
.. data:: parallelCollectionScan.cursors
An array with one or more cursors returned with the command.
.. data:: parallelCollectionScan.cursors.cursor
For each cursor returned, a document with details about the cursor.
.. data:: parallelCollectionScan.cursors.cursor.firstBatch
An empty first batch is useful for quickly returning a cursor or
failure message without doing significant server-side work. See
:ref:`cursor batches <cursor-batches>`.
.. data:: parallelCollectionScan.cursors.cursor.ns
The namespace for each cursor.
.. data:: parallelCollectionScan.cursors.cursor.id
The unique id for each cursor.
.. data:: parallelCollectionScan.cursors.ok
The status of each cursor returned with the command.
.. data:: parallelCollectionScan.ok
A value of ``1`` indicates the :dbcommand:`parallelCollectionScan`
command succeeded. A value of ``0`` indicates an error.