MATLAB: Parfor starting a new parallel pool at every call

parforparpool

Hi, I am running MATLAB on a cluster, and noticed my jobs suddenly becoming very slow. When I looked at the logs it is a lot of (Starting parallel pool (parpool) using the 'local' profile) spam. It seems that MATLAB is starting a new parallel pool every time I call a parfor loop.
When I run MATLAB on the front end I encounter the same problem, e.g.:
>> parfor i=1:2;disp(i);end
Starting parallel pool (parpool) using the 'local' profile ...
     2
       1
>> parfor i=1:2;disp(i);end
Starting parallel pool (parpool) using the 'local' profile ...
     2
       1
>> parfor i=1:2;disp(i);end
Starting parallel pool (parpool) using the 'local' profile ...
     2
Any idea what could be happening? (running '9.4.0.902940 (R2018a) Update 4')

Best Answer

Do this once in your MATLAB command line to set the default setting to :
    ps = parallel.Settings;
    ps.Pool.AutoCreate = false; %do not autocreate parpool when encountering a |parfor|
    ps.Pool.IdleTimeout = Inf;  %do not shutdown parpool after Inf idle time
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