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Posted to user@zookeeper.apache.org by Scott Fines <sc...@gmail.com> on 2013/05/23 15:47:34 UTC
Understanding event interleaving
Hello all,
This is perhaps a silly question, but one I'm not clear on.
Suppose you have two clients (R and W), and they are interacting through znode Z. Now consider the following situation:
0. Z at version 1
1. R begins getData(Z) (attach Watcher)
2. W begins setData(Z)
3. W completed setData(Z) successfully --e.g. the client call returns with no errors
4. R completes getData(Z) successfully -- e.g. the client call returns with no errors
My questions are then:
1. What version of data will R receive? Version 1, or Version 2? My assumption here is that R would receive version 1 of the data--is that correct?
2. Does R's watch fire with the changes made by W? If so, is a WatchEvent delivered all the way to the caller? A comment made on ZOOKEEPER-1505 (https://issues.apache.org/jira/browse/ZOOKEEPER-1505) implies that it would not, but I'm unclear if that is in reference to the proposed changes or not.
Thanks for your help!
Scott Fines
Re: Understanding event interleaving
Posted by Bahman Kalali <ba...@gmail.com>.
If I understand well your scenario, R will receive Version 2 and and event
is delivered to caller (R). In this scenario, the thread that has
registered the watch on node Z has to still be alive to receive the event.
BR//Bahman
On Thu, May 23, 2013 at 8:47 AM, Scott Fines <sc...@gmail.com> wrote:
> Hello all,
>
> This is perhaps a silly question, but one I'm not clear on.
>
> Suppose you have two clients (R and W), and they are interacting through
> znode Z. Now consider the following situation:
>
> 0. Z at version 1
> 1. R begins getData(Z) (attach Watcher)
> 2. W begins setData(Z)
> 3. W completed setData(Z) successfully --e.g. the client call returns with
> no errors
> 4. R completes getData(Z) successfully -- e.g. the client call returns
> with no errors
>
> My questions are then:
>
> 1. What version of data will R receive? Version 1, or Version 2? My
> assumption here is that R would receive version 1 of the data--is that
> correct?
>
> 2. Does R's watch fire with the changes made by W? If so, is a WatchEvent
> delivered all the way to the caller? A comment made on ZOOKEEPER-1505 (
> https://issues.apache.org/jira/browse/ZOOKEEPER-1505) implies that it
> would not, but I'm unclear if that is in reference to the proposed changes
> or not.
>
> Thanks for your help!
>
> Scott Fines
>
>
>
Re: Understanding event interleaving
Posted by Scott Fines <sc...@gmail.com>.
Thanks Flavio,Bahman, that was a great help. Turned out to be pretty straightforward, after all.
Scott
--
Scott Fines
Sent with Sparrow (http://www.sparrowmailapp.com/?sig)
On Thursday, May 23, 2013 at 9:04 AM, Flavio Junqueira wrote:
> Hi Scott,
>
> The R client could receive either version 1 or version 2. In the case it receives version 1, it will receive the notification for the version 2 change once the server the client is connected to receives the update. If the getData returns version 2 instead, it won't get the watch triggered by the setData of steps 2 and 3 below. It should get it triggered by a future update, though, assuming there is one.
>
> -Flavio
>
> -----Original Message-----
> From: Scott Fines [mailto:scottfines@gmail.com]
> Sent: 23 May 2013 14:48
> To: user@zookeeper.apache.org (mailto:user@zookeeper.apache.org)
> Subject: Understanding event interleaving
>
> Hello all,
>
> This is perhaps a silly question, but one I'm not clear on.
>
> Suppose you have two clients (R and W), and they are interacting through znode Z. Now consider the following situation:
>
> 0. Z at version 1
> 1. R begins getData(Z) (attach Watcher)
> 2. W begins setData(Z)
> 3. W completed setData(Z) successfully --e.g. the client call returns with no errors
> 4. R completes getData(Z) successfully -- e.g. the client call returns with no errors
>
> My questions are then:
>
> 1. What version of data will R receive? Version 1, or Version 2? My assumption here is that R would receive version 1 of the data--is that correct?
>
> 2. Does R's watch fire with the changes made by W? If so, is a WatchEvent delivered all the way to the caller? A comment made on ZOOKEEPER-1505 (https://issues.apache.org/jira/browse/ZOOKEEPER-1505) implies that it would not, but I'm unclear if that is in reference to the proposed changes or not.
>
> Thanks for your help!
>
> Scott Fines
RE: Understanding event interleaving
Posted by Flavio Junqueira <fp...@yahoo.com>.
Hi Scott,
The R client could receive either version 1 or version 2. In the case it receives version 1, it will receive the notification for the version 2 change once the server the client is connected to receives the update. If the getData returns version 2 instead, it won't get the watch triggered by the setData of steps 2 and 3 below. It should get it triggered by a future update, though, assuming there is one.
-Flavio
-----Original Message-----
From: Scott Fines [mailto:scottfines@gmail.com]
Sent: 23 May 2013 14:48
To: user@zookeeper.apache.org
Subject: Understanding event interleaving
Hello all,
This is perhaps a silly question, but one I'm not clear on.
Suppose you have two clients (R and W), and they are interacting through znode Z. Now consider the following situation:
0. Z at version 1
1. R begins getData(Z) (attach Watcher)
2. W begins setData(Z)
3. W completed setData(Z) successfully --e.g. the client call returns with no errors
4. R completes getData(Z) successfully -- e.g. the client call returns with no errors
My questions are then:
1. What version of data will R receive? Version 1, or Version 2? My assumption here is that R would receive version 1 of the data--is that correct?
2. Does R's watch fire with the changes made by W? If so, is a WatchEvent delivered all the way to the caller? A comment made on ZOOKEEPER-1505 (https://issues.apache.org/jira/browse/ZOOKEEPER-1505) implies that it would not, but I'm unclear if that is in reference to the proposed changes or not.
Thanks for your help!
Scott Fines