A parallel pool is a set of MATLAB® workers on a compute
cluster or desktop. By default, a parallel pool starts automatically
when needed by parallel language features such as
You can specify the default pool size and cluster in your parallel
preferences. The preferences panel displays your pool size and cluster
when you select Parallel Preferences in
the Parallel menu. You can change pool
size and cluster in the Parallel menu.
Alternatively, you can choose cluster and pool size using
on the MATLAB command line. See the image for more detail.
The workers in a parallel pool can be used interactively and
communicate with each other during the lifetime of the job. You can
parpool jobs in the Job Monitor. While
these pool workers are reserved for your interactive use, they are
not available to other users. You can have only one parallel pool
at a time from a MATLAB client session. In MATLAB, the current
parallel pool is represented by a parallel.Pool object.
By default, a parallel pool starts automatically when needed by certain parallel language features. Many functions can automatically start a parallel pool, including:
Your parallel preferences specify which cluster the pool runs on, and the preferred number of workers in the pool. To access your preferences, on the Home tab, in the Environment section, click Parallel > Parallel Preferences.
In your parallel preferences, you can turn off the option for the pool to open or close automatically. If you choose not to have the pool open automatically, you can control the pool with the following techniques.
You can use the parallel status indicator in the lower left corner of the MATLAB desktop to start a parallel pool manually.
Click the indicator icon, and select Start Parallel Pool. The pool size and cluster are specified by your parallel preferences and default cluster. Your default cluster is indicated by a check mark on the Parallel > Default Cluster menu.
The menu options are different when a pool is running. You can:
View the number of workers and cluster name
Change the time until automatic shut-down
Shut down the parallel pool
To stop a pool, you can also select Shut Down Parallel Pool.
Start a Parallel Pool. You can start and stop a parallel pool programmatically by using default settings or specifying alternatives.
To open a parallel pool based on your preference settings:
To open a pool of a specific size:
To use a cluster other than your default and specify where the pool runs:
Shut Down a Parallel Pool. To get the current parallel pool and use that object when you want to shut down the pool:
p = gcp; delete(p)
Ensure That No Parallel Pool Is Running. When you issue the command
arguments, you might inadvertently open a pool. To avoid this problem:
There are several places to specify pool size. Several factors might limit the size of a pool. The actual size of your parallel pool is determined by the combination of the following:
Licensing or cluster size
The maximum limit on the number of workers in a pool is restricted by the number of workers in your cluster. This limit might be determined by the number of MATLAB Parallel Server™ licenses available. In the case of MATLAB Job Scheduler, the limit might be determined by the number of workers running in the cluster. A local cluster running on the client machine requires no licensing beyond the one for Parallel Computing Toolbox™. The limit on the number of workers is high enough to support the range of known desktop hardware.
Cluster profile number of workers (
A cluster object can set a hard limit on the number of workers, which you specify in the cluster profile. Even if you request more workers at the command line or in your preferences, you cannot exceed the limit set in the applicable profile. Attempting to exceed this number generates an error.
If you specify a pool size at the command line, you override the setting of your preferences. This value must fall within the limits of the applicable cluster profile.
If you do not specify a pool size at the command line, MATLAB attempts to start a pool with size determined by your parallel preferences. This value is a preference, not a requirement or a request for a specific number of workers. So if a pool cannot start with as many workers as called for in your preferences, you get a smaller pool without any errors. You can set the value of the Preferred number of workers to a large number, so that it never limits the size of the pool that is created. If you need an exact number of workers, specify the number at the command line.
For selection of the cluster on which the pool runs, precedence is determined by the following.
The command-line cluster object argument overrides
the default profile setting and uses the cluster identified by the
c = parcluster('MyProfile'); p = parpool(c);
The cluster is specified in the default profile.
p = parpool;