Is continually writing to a file detrimental to the performance of a program?












0















Imagine a parallel "high performance program" that reads in files, each process performs a task on the input data and then each process writes an output for the task to a single shared output file before repeating this procedure.



In terms of performance, is it inefficient to write the outputs to a file as each process finishes a task?



Would it be more efficient to store the results in an array and write the array to an output file at the end?










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  • 1





    You could try creating a MVCE for both scenarios and do some measurements (e. g. use a performance profiler and/or a memory profiler and/or some Stopwatch instances).

    – Uwe Keim
    Nov 22 '18 at 22:18













  • Please do not add "Thank you" to questions.

    – Uwe Keim
    Nov 22 '18 at 22:18













  • The answer depends on context. It can be either way. Code it both ways and benchmark them to see.

    – Craig Estey
    Nov 22 '18 at 22:24











  • If your platform supports memory-mapped files, you don't have to choose.

    – EOF
    Nov 22 '18 at 23:28











  • I read the first paragraph and now I'm imagining 65,356 processes each taking its turn to write to the single shared output file. Even with far fewer processes in play this is going to look pretty much like a serial program and it's not a good outline design.

    – High Performance Mark
    Nov 23 '18 at 8:32
















0















Imagine a parallel "high performance program" that reads in files, each process performs a task on the input data and then each process writes an output for the task to a single shared output file before repeating this procedure.



In terms of performance, is it inefficient to write the outputs to a file as each process finishes a task?



Would it be more efficient to store the results in an array and write the array to an output file at the end?










share|improve this question




















  • 1





    You could try creating a MVCE for both scenarios and do some measurements (e. g. use a performance profiler and/or a memory profiler and/or some Stopwatch instances).

    – Uwe Keim
    Nov 22 '18 at 22:18













  • Please do not add "Thank you" to questions.

    – Uwe Keim
    Nov 22 '18 at 22:18













  • The answer depends on context. It can be either way. Code it both ways and benchmark them to see.

    – Craig Estey
    Nov 22 '18 at 22:24











  • If your platform supports memory-mapped files, you don't have to choose.

    – EOF
    Nov 22 '18 at 23:28











  • I read the first paragraph and now I'm imagining 65,356 processes each taking its turn to write to the single shared output file. Even with far fewer processes in play this is going to look pretty much like a serial program and it's not a good outline design.

    – High Performance Mark
    Nov 23 '18 at 8:32














0












0








0








Imagine a parallel "high performance program" that reads in files, each process performs a task on the input data and then each process writes an output for the task to a single shared output file before repeating this procedure.



In terms of performance, is it inefficient to write the outputs to a file as each process finishes a task?



Would it be more efficient to store the results in an array and write the array to an output file at the end?










share|improve this question
















Imagine a parallel "high performance program" that reads in files, each process performs a task on the input data and then each process writes an output for the task to a single shared output file before repeating this procedure.



In terms of performance, is it inefficient to write the outputs to a file as each process finishes a task?



Would it be more efficient to store the results in an array and write the array to an output file at the end?







c parallel-processing io hpc






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share|improve this question













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share|improve this question








edited Nov 22 '18 at 22:39







HCF3301

















asked Nov 22 '18 at 22:17









HCF3301HCF3301

456




456








  • 1





    You could try creating a MVCE for both scenarios and do some measurements (e. g. use a performance profiler and/or a memory profiler and/or some Stopwatch instances).

    – Uwe Keim
    Nov 22 '18 at 22:18













  • Please do not add "Thank you" to questions.

    – Uwe Keim
    Nov 22 '18 at 22:18













  • The answer depends on context. It can be either way. Code it both ways and benchmark them to see.

    – Craig Estey
    Nov 22 '18 at 22:24











  • If your platform supports memory-mapped files, you don't have to choose.

    – EOF
    Nov 22 '18 at 23:28











  • I read the first paragraph and now I'm imagining 65,356 processes each taking its turn to write to the single shared output file. Even with far fewer processes in play this is going to look pretty much like a serial program and it's not a good outline design.

    – High Performance Mark
    Nov 23 '18 at 8:32














  • 1





    You could try creating a MVCE for both scenarios and do some measurements (e. g. use a performance profiler and/or a memory profiler and/or some Stopwatch instances).

    – Uwe Keim
    Nov 22 '18 at 22:18













  • Please do not add "Thank you" to questions.

    – Uwe Keim
    Nov 22 '18 at 22:18













  • The answer depends on context. It can be either way. Code it both ways and benchmark them to see.

    – Craig Estey
    Nov 22 '18 at 22:24











  • If your platform supports memory-mapped files, you don't have to choose.

    – EOF
    Nov 22 '18 at 23:28











  • I read the first paragraph and now I'm imagining 65,356 processes each taking its turn to write to the single shared output file. Even with far fewer processes in play this is going to look pretty much like a serial program and it's not a good outline design.

    – High Performance Mark
    Nov 23 '18 at 8:32








1




1





You could try creating a MVCE for both scenarios and do some measurements (e. g. use a performance profiler and/or a memory profiler and/or some Stopwatch instances).

– Uwe Keim
Nov 22 '18 at 22:18







You could try creating a MVCE for both scenarios and do some measurements (e. g. use a performance profiler and/or a memory profiler and/or some Stopwatch instances).

– Uwe Keim
Nov 22 '18 at 22:18















Please do not add "Thank you" to questions.

– Uwe Keim
Nov 22 '18 at 22:18







Please do not add "Thank you" to questions.

– Uwe Keim
Nov 22 '18 at 22:18















The answer depends on context. It can be either way. Code it both ways and benchmark them to see.

– Craig Estey
Nov 22 '18 at 22:24





The answer depends on context. It can be either way. Code it both ways and benchmark them to see.

– Craig Estey
Nov 22 '18 at 22:24













If your platform supports memory-mapped files, you don't have to choose.

– EOF
Nov 22 '18 at 23:28





If your platform supports memory-mapped files, you don't have to choose.

– EOF
Nov 22 '18 at 23:28













I read the first paragraph and now I'm imagining 65,356 processes each taking its turn to write to the single shared output file. Even with far fewer processes in play this is going to look pretty much like a serial program and it's not a good outline design.

– High Performance Mark
Nov 23 '18 at 8:32





I read the first paragraph and now I'm imagining 65,356 processes each taking its turn to write to the single shared output file. Even with far fewer processes in play this is going to look pretty much like a serial program and it's not a good outline design.

– High Performance Mark
Nov 23 '18 at 8:32












2 Answers
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oldest

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1














This is problem where full IO disk read write has to be exploited without delays from client processes or threads. If Std C library calls are used it uses memory buffer that gets flushed at newline or fflush() call is made. If the data is not big enough using array is efficient that can be written to file at the end so performance demanding task will not suffer IO delays.






share|improve this answer































    -2














    Files are usually slower than RAM. However, how much slower? If it's less than 1% slowdown, most people would not care. If it's 50% slowdown, some people would still not care.



    As always with performance, measure it one way and the other, and then decide whether the difference is significant. The decision will usually depend on factors which are highly application-specific.






    share|improve this answer























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      2 Answers
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      2 Answers
      2






      active

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      active

      oldest

      votes






      active

      oldest

      votes









      1














      This is problem where full IO disk read write has to be exploited without delays from client processes or threads. If Std C library calls are used it uses memory buffer that gets flushed at newline or fflush() call is made. If the data is not big enough using array is efficient that can be written to file at the end so performance demanding task will not suffer IO delays.






      share|improve this answer




























        1














        This is problem where full IO disk read write has to be exploited without delays from client processes or threads. If Std C library calls are used it uses memory buffer that gets flushed at newline or fflush() call is made. If the data is not big enough using array is efficient that can be written to file at the end so performance demanding task will not suffer IO delays.






        share|improve this answer


























          1












          1








          1







          This is problem where full IO disk read write has to be exploited without delays from client processes or threads. If Std C library calls are used it uses memory buffer that gets flushed at newline or fflush() call is made. If the data is not big enough using array is efficient that can be written to file at the end so performance demanding task will not suffer IO delays.






          share|improve this answer













          This is problem where full IO disk read write has to be exploited without delays from client processes or threads. If Std C library calls are used it uses memory buffer that gets flushed at newline or fflush() call is made. If the data is not big enough using array is efficient that can be written to file at the end so performance demanding task will not suffer IO delays.







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Nov 23 '18 at 2:43









          anandanand

          1375




          1375

























              -2














              Files are usually slower than RAM. However, how much slower? If it's less than 1% slowdown, most people would not care. If it's 50% slowdown, some people would still not care.



              As always with performance, measure it one way and the other, and then decide whether the difference is significant. The decision will usually depend on factors which are highly application-specific.






              share|improve this answer




























                -2














                Files are usually slower than RAM. However, how much slower? If it's less than 1% slowdown, most people would not care. If it's 50% slowdown, some people would still not care.



                As always with performance, measure it one way and the other, and then decide whether the difference is significant. The decision will usually depend on factors which are highly application-specific.






                share|improve this answer


























                  -2












                  -2








                  -2







                  Files are usually slower than RAM. However, how much slower? If it's less than 1% slowdown, most people would not care. If it's 50% slowdown, some people would still not care.



                  As always with performance, measure it one way and the other, and then decide whether the difference is significant. The decision will usually depend on factors which are highly application-specific.






                  share|improve this answer













                  Files are usually slower than RAM. However, how much slower? If it's less than 1% slowdown, most people would not care. If it's 50% slowdown, some people would still not care.



                  As always with performance, measure it one way and the other, and then decide whether the difference is significant. The decision will usually depend on factors which are highly application-specific.







                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered Nov 22 '18 at 22:22









                  anatolyganatolyg

                  16.9k44590




                  16.9k44590






























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