File Journalling Latency

[Michael Barker]

Hi,

One of my colleagues (Mark Price) has done some deep diving into the latency of journalling to disk.

http://epickrram.blogspot.co.uk/2015/05/improving-journalling-latency.html

http://epickrram.blogspot.co.uk/2015/07/seek-write-vs-pwrite.html

Mike.

[Remko Popma]

Very nice! Keep 'em coming!

[Greg Young]

I just wanted to bring up one small thing with pwrite that can
actually screw up measurements.

If you open with O_APPEND on linux pwrite will ignore the position
parameter and always append. I got bit by this where one measurement
ended up being random access the other was always sequential :) Note
this is not in line with posix, posix states that O_APPEND should not
have any affect.

Cheers,

Greg

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