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On 13 Feb 2017, at 17:16, Sai Vishwas wrote:

> Hi,
>
>      I was reading about the replicator process that runs at regular
> intervals. I would like to know if my understanding of it is correct .

Yep, you've got a good understanding.

>
>      This is my understanding :  Since it is partitions that are
> replicated, the replicator process uses the hash of the partition's
> contents to check whether the replicas are all up to date, i.e all changes
> have been updated on all three replica partitions. In case, an operation
> has failed on one node, then the partition on that node will have an older
> 'last updated timestamp' and also its hash will differ from that of the
> partitions on which the operation succeeded. Once, the replicator sees that
> the 2 partitions have a different hash value, it realizes that the one with
> older timestamp has to be updated and hence checks as to which all files
> have to be updated and then rsyncs only those particular files.
>
>    Is this right, or does it rsync the entire partition?

Both, sortof. Swift will start an rsync of the partition suffix (up to 4096 of these per partition), but because of the magic of rsync, only the changed files will be transferred.

>
>    Apart from generating this hash value for easy change detection, and
> assigning weights to nodes, for what other purposes does the concept of
> 'swift partitions' come into help ?

The partitions are primarily used for data balance across all of the available storage devices and distribution across different failure domains.

Read more at http://docs.openstack.org/developer/swift/overview_ring.html

>
>
> Thank you. Have a great day.
>
> Regards,
> Sai Vishwas
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