Re: CephFS: 'ls -alR' performance terrible unless Linux cache flushed

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On 16/06/2015 12:11, negillen negillen wrote:
This is quite a problem because we have several applications that need to access a large number of files and when we set them to work on CephFS latency skyrockets.

The question of what "access" means here is key. Especially, whether you need the "-l" part of "ls -l". A plain "ls" is one readdir operation, adding "-l" turns it into N stat operations.

This is something that distributed filesystems can be optimised to cope with (e.g. by batching the stats and associated locking, or Lustre's statahead), but frequently applications can simply avoid "-l", if all they really needed to do was list the files.

John
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