[Gluster-users] Read from fastest node only

David Cunningham dcunningham at voisonics.com
Wed Jul 28 02:49:16 UTC 2021

Hi Yaniv,

It may be my lack of knowledge, but I can't see how the fastest response
time could differ from file to file. If that's true then it would be enough
to only periodically test which node is fastest for this client, not having
to do it for every single read.

Thanks for the tip about read-hash-mode. I see the help is as below. Value
4 may help, but not if the latency is tested for every file read. Value 0
may help, but it depends how the children are ordered. Does anyone know
more about how these work?

Option: cluster.read-hash-mode
Default Value: 1
Description: inode-read fops happen only on one of the bricks in replicate.
AFR will prefer the one computed using the method specified using this
0 = first readable child of AFR, starting from 1st child.
1 = hash by GFID of file (all clients use same subvolume).
2 = hash by GFID of file and client PID.
3 = brick having the least outstanding read requests.
4 = brick having the least network ping latency.

Thanks again.

On Tue, 27 Jul 2021 at 19:16, Yaniv Kaul <ykaul at redhat.com> wrote:

> On Tue, Jul 27, 2021 at 9:50 AM David Cunningham <
> dcunningham at voisonics.com> wrote:
>> Hello,
>> We have a replicated GlusterFS cluster, and my understanding is that the
>> GlusterFS FUSE client will check the file with all nodes before doing a
>> read.
>> For our application it is not actually critical to be certain of having
>> the latest version of a file, and it would be preferable to speed up the
>> read by simply reading the file from the fastest node. This would be
>> especially beneficial if some of the other nodes have higher latency from
>> the client.
> How do you define, in real time, per file, which is the fastest node?
> Maybe you are looking for read-hash-mode volume option?
> Y.
>> Is it possible to do this? Thanks in advance for any assistance.
>> --
>> David Cunningham, Voisonics Limited
>> http://voisonics.com/
>> USA: +1 213 221 1092
>> New Zealand: +64 (0)28 2558 3782
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David Cunningham, Voisonics Limited
USA: +1 213 221 1092
New Zealand: +64 (0)28 2558 3782
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