.z.pd: x

Where q has been started with secondary processes for use in parallel processing, x is

• an int vector of handles to secondary processes
• a function that returns a list of handles to those secondary processes

For evaluating the function passed to peach or ':, kdb+ gets the handles to the secondary processes by calling .z.pd[].

q)/open connections to 4 processes on the localhost
q).z.pd:`u#hopen each 20000+til 4

The int vector (returned by) x must have the unique attribute set.

A more comprehensive setup might be

q).z.pd:{n:abs system"s";$[n=count handles;handles;[hclose each handles;:handles::`u#hopen each 20000+til n]]}
q).z.pc:{handles::`u#handles except x;}
q)handles:`u#`int$();

Note that (since V3.1) the worker processes are not started automatically by kdb+.