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Top Forums UNIX for Advanced & Expert Users Help optimizing sort of large files Post 302925546 by kogorman3 on Monday 17th of November 2014 09:19:12 PM
Old 11-17-2014
Quote:
Originally Posted by Corona688
Not really.

If your files can fit in memory, either way you do it -- cache or sort buffers -- it will be held in RAM. Yes, too many files at once is bad since the disk has to seek them individually.
I'm testing with my idea of a small file: 13 GB. My targets are more like TB-sized. These are the cases that motivate optimizing GNU sort. For modest-sized files, I wouldn't bother.

Quote:
I don't think this has much to do with the size of the temp files as much as their number. Doing a lot of seeking on a non-SSD disk makes its performance really bad. I once measured a disk's random read performance with caching disabled -- hopping from one sector to another, reading then moving, gets you fifty kilobytes per second on a disk good for 100MB/s. Using all available RAM is about as bad as turning off caching, by the way. Worse actually -- memory pressure will start pushing out useful things, making programs wait pointlessly for bits of code to return to them at need.
Size and number are linked. If they're bigger, there are fewer of them. So would love for the cache to contain all of the data from files being merged. I don't know how to do it, but I'm hoping my data will guide me to it indirectly.

Quote:
Cache could also explain the differing times your runs take. If there's significant parts of your file left in cache, that could speed up the next run.
True. I do not do anything to clear the caches before each run, but the tests are done by scripts that always do them in the same order, so I would expect more uniformity than I've seen so far.
 

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CACHEINFO(5)							AFS File Reference						      CACHEINFO(5)

NAME
cacheinfo - Defines configuration parameters for the Cache Manager DESCRIPTION
The cacheinfo file defines configuration parameters for the Cache Manager, which reads the file as it initializes. The file contains a single line of ASCII text and must reside in the /etc/openafs directory. Use a text editor to create it during initial configuration of the client machine; the required format is as follows: <mount>:<cache>:<size> where <mount> Names the local disk directory at which the Cache Manager mounts the AFS namespace. It must exist before the afsd program runs. The conventional value is /afs. Using any other value prevents traversal of pathnames that begin with /afs (such as pathnames to files in foreign cells that do use the conventional name). The -mountdir argument to the afsd command overrides this value. <cache> Names the local disk directory to use as a cache. It must exist before the afsd program runs. The standard value is /usr/vice/cache, but it is acceptable to substitute a directory on a partition with more available space. Although the Cache Manager ignores this field when configuring a memory cache, a value must always appear in it. The -cachedir argument to the afsd command overrides this value. <size> Specifies the cache size as a number of 1-kilobyte blocks. Larger caches generally yield better performance, but a disk cache must not exceed 90% of the space available on the cache partition (85% for AIX systems), and a memory cache must use no more than 25% of available machine memory. The -blocks argument to the afsd command overrides this value. To reset cache size without rebooting on a machine that uses disk caching, use the fs setcachesize command. To display the current size of a disk or memory cache between reboots, use the fs getcacheparms command. EXAMPLES
The following example cacheinfo file mounts the AFS namespace at /afs, establishes a disk cache in the /usr/vice/cache directory, and defines cache size as 50,000 1-kilobyte blocks. /afs:/usr/vice/cache:50000 SEE ALSO
afsd(8), fs_getcacheparms(1), fs_setcachesize(1) COPYRIGHT
IBM Corporation 2000. <http://www.ibm.com/> All Rights Reserved. This documentation is covered by the IBM Public License Version 1.0. It was converted from HTML to POD by software written by Chas Williams and Russ Allbery, based on work by Alf Wachsmann and Elizabeth Cassell. OpenAFS 2012-03-26 CACHEINFO(5)
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