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Full Discussion: Help optimizing sort of large files
Top Forums UNIX for Advanced & Expert Users Help optimizing sort of large files Post 302926737 by DGPickett on Wednesday 26th of November 2014 01:53:38 PM
Old 11-26-2014
Well, you are approaching the ideal, that the first pass create N files with one sorted string on each, and the next pass is the final merge. If you fall short, then there needs to be at least one intermediate pass to merge to fewer strings per file. Each pass has to take the io time to copy the entire file, so less passes is better.

Head moition is an old phobia, perhaps persisting because you can still hear the seeks on some drives. Ofthe the average seek is less than the average latency. Modern drives cache everything once they arrive on cylinder, so some latency may be paid back in fast access to the cached, later sectors. Large AU and smart buffering in HW and software helps ensure more data for each possible seek. If the disk is not defragged, and especially if it has a low AU, you may have a lot of seeks in a sequential read or write.
 

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LEARN ABOUT OSX

seeksize.d

seeksize.d(1m)							   USER COMMANDS						    seeksize.d(1m)

NAME

       seeksize.d - print disk event seek report. Uses DTrace.

SYNOPSIS

       seeksize.d

DESCRIPTION

       seeksize.d is a simple DTrace program to print a report of disk event seeks by process.

       This can be used to identify whether processes are accessing the disks in a "random" or "sequential" manner. Sequential is often desirable,
       indicated by mostly zero length seeks.

       Since this uses DTrace, only users with root privileges can run this command.

EXAMPLES

       Sample until Ctrl-C is hit then print report,
	      # seeksize.d

FIELDS

       PID    process ID

       CMD    command and argument list

       value  distance in disk blocks (sectors)

       count  number of I/O operations

DOCUMENTATION

       See the DTraceToolkit for further documentation under the Docs directory. The DTraceToolkit docs may include full worked examples with ver-
       bose descriptions explaining the output.

EXIT

       seeksize.d will sample until Ctrl-C is hit.

AUTHOR

       Brendan Gregg [Sydney, Australia]

SEE ALSO

       iosnoop(1M), bitesize.d(1M), dtrace(1M)

version 0.95							   May 14, 2005 						    seeksize.d(1m)
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