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From Alexander Shraer <shra...@gmail.com>
Subject Re: Sync question
Date Tue, 05 Nov 2013 23:33:26 GMT
The guarantee when using "sync + read" and updates is that the read
will see any update that completes before the sync starts (if the
update starts after the sync it is concurrent and may be reordered
even with ACID). ZooKeeper guarantees much more than eventual
consistency... if you're using sync it guarantees linearizability
between "sync + read" pairs and updates.

On Tue, Nov 5, 2013 at 11:38 AM, Adrian Osullivan
<adrian.osullivan@db.com> wrote:
> Thanks, just wanted to confirm that. Some of the things you read about sync seem to suggest
the next client read will be up to date but this is not strictly true.  This isn't a fault
of course, but by design.
>
> -----Original Message-----
> From: Jordan Zimmerman [mailto:jordan@jordanzimmerman.com]
> Sent: Tuesday, November 05, 2013 2:36 PM
> To: user@zookeeper.apache.org
> Subject: Re: Sync question
>
>> So it seems there is no mechanism is zookeeper for guaranteeing a read is truly up
to date with the leader. Is this true?
>
> ZooKeeper is an eventually consistent system, not an ACID system. So, true.
>
> On Nov 5, 2013, at 11:31 AM, Adrian Osullivan <adrian.osullivan@db.com> wrote:
>
>> Hi everyone!  The zk API's sync() method brings the server up to date with the leader.
 So the next client read should give the up to date value.  But in the time between completing
the sync and starting the read, another client may have sent an update and the server one
is connected to may again lag the leader.  So it seems there is no mechanism is zookeeper
for guaranteeing a read is truly up to date with the leader. Is this true?
>>
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>
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distribution of the material in this communication is strictly forbidden.
>
> Deutsche Bank does not render legal or tax advice, and the information contained in this
communication should not be regarded as such.

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