[Openstack] Writes are faster than reads in Swift

Zhenhua (Gerald) Guo jenvor at gmail.com
Wed Dec 28 17:19:31 UTC 2011

Thanks for explaining it.
I read the source code and confirmed that read operations incur more
drop_cache calls than write operations.  However, I am not sure
whether the additional calls result in significant overhead. Need some
tests to verify.


On Tue, Dec 13, 2011 at 11:32 PM, Michael Barton
<mike-launchpad at weirdlooking.com> wrote:
> I can't explain it off the top of my head.
> I don't have a swift installation to play with at the moment, but it's
> conceivable that posix_fadvise is slower than we expect (drop_cache is
> called more frequently during reads than writes, iirc).  That could be
> tested by making drop_cache a no-op in the object server.
> Or running the object server under a profiler during both operations
> might shed some light on what is taking so much time.
> --Mike
> On Mon, Dec 12, 2011 at 8:44 AM, Zhenhua (Gerald) Guo <jenvor at gmail.com> wrote:
>> Hi, folks
>>  Recently, I have run some read/write tests for large files (400GB)
>> in Swift.  I found that writes were always faster than reads, which is
>> kinda counter-intuitive. What may be the cause?
>>  Has anyone else seen the same problem?
>> Gerald
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