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Each Parallel issue
Follows https://code.kx.com/q/basics/peach/,
The result of
m':[x]is exactly the same asm'[x]. If no secondary tasks are available, performance is the same as well.but m’:[x] more fast and less memory used. Is not m'[x] parallel execuation??…
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1 Reply
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m'[x]is not parallel executionThere can be cases where the overhead of using multiple threads can make execution slower than single threaded. (.i.e performing many small operations)
.Q.fcis available to help in some of these cases.https://code.kx.com/q/ref/dotq/#qfc-parallel-on-cut
If you measure memory usage with
tsnote that it only sees usage in main thread. It does not sum usage from all threads. So you cannot compare results directly.q)\ts {til 10000000;x}'[til 1000] // \ts shows real memory usage 5395 134250848 q)\ts {til 10000000;x}':[til 1000] // \ts only sees memory usage in main thread - not the sum of threads 5612 33408q)\ts {x}'[til 100000] // Single core 8 4746288 q)\ts {x}':[til 100000] // Slower due to parallel overhead 13 4194864 q)\ts .Q.fc[{x}][til 100000] //Faster way to use multiple cores 1 3146512
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