Thanks for the explanations.
Really good explanation in the mail threads.

I feel like you missed the part of my question (Or maybe I didn't understand 
the answer) about Full Snapshot.
I'll compare to a DB.
In an SqlServer I can run:
"
ALTER DATABASE MyDatabase
SET ALLOW_SNAPSHOT_ISOLATION ON
"

This will mean that if I have 5 different tables, when starting a transaction, 
I get a full snapshot of all five.
I am looking for the equivalent in MD-SAL. 
Not only a snapshot of one data tree, but a snapshot of all data trees for a 
given point of time.

When you said:
"Transactions do take snapshots but they are inmemory"
Do you mean a snapshot of all the data trees? Or the specific one you read from?

-----Original Message-----
From: Muthukumaran K [mailto:muthukumara...@ericsson.com] 
Sent: Monday, September 19, 2016 8:15 AM
To: Sela, Guy <guy.s...@hpe.com>; Robert Varga <n...@hq.sk>; Tom Pantelis 
<tompante...@gmail.com>
Cc: controller-dev <controller-dev@lists.opendaylight.org>
Subject: RE: [controller-dev] [documentation] Questions about ODL clustering

Hi Guy, 

There is a jmx operation (can be invoked via JConsole) to dump the snapshot on 
demand on per shard basis for config DS shards. 

Transactions do take snapshots but they are inmemory. As you surmise, 
transaction-level snapshotting is "Isolation" part of ACID.  
A good explanation was given by Robert in following mail threads  

https://lists.opendaylight.org/pipermail/controller-dev/2016-July/012298.html
https://lists.opendaylight.org/pipermail/controller-dev/2016-July/012331.html

Regards
Muthu


-----Original Message-----
From: controller-dev-boun...@lists.opendaylight.org 
[mailto:controller-dev-boun...@lists.opendaylight.org] On Behalf Of Sela, Guy
Sent: Sunday, September 18, 2016 5:59 PM
To: Robert Varga; Tom Pantelis
Cc: controller-dev
Subject: Re: [controller-dev] [documentation] Questions about ODL clustering

What I mean is to be able to create a snapshot of the entire state and not only 
a specific data tree.


-----Original Message-----
From: controller-dev-boun...@lists.opendaylight.org 
[mailto:controller-dev-boun...@lists.opendaylight.org] On Behalf Of Sela, Guy
Sent: Sunday, September 18, 2016 3:25 PM
To: Robert Varga <n...@hq.sk>; Tom Pantelis <tompante...@gmail.com>
Cc: controller-dev <controller-dev@lists.opendaylight.org>
Subject: Re: [controller-dev] [documentation] Questions about ODL clustering

Thanks.
Are there any plans to do something regarding snapshots that resembles Snapshot 
Isolation in a DB?

For example:
https://msdn.microsoft.com/en-us/library/tcbchxcb(v=vs.110).aspx

-----Original Message-----
From: controller-dev-boun...@lists.opendaylight.org 
[mailto:controller-dev-boun...@lists.opendaylight.org] On Behalf Of Robert Varga
Sent: Sunday, September 18, 2016 1:28 PM
To: Sela, Guy <guy.s...@hpe.com>; Tom Pantelis <tompante...@gmail.com>
Cc: controller-dev <controller-dev@lists.opendaylight.org>
Subject: Re: [controller-dev] [documentation] Questions about ODL clustering

On 09/15/2016 05:17 PM, Sela, Guy wrote:
> ReadOnlyTransaction tx = db.newReadOnlyTransaction();
> 
> CheckedFuture<Optional<DataObject>, ReadFailedException> read1 = 
> tx.read(X, Y)
> 
> CheckedFuture<Optional<DataObject>, ReadFailedException> read2 = 
> tx.read(Z, H)
> 
>  
> 
> read1 and read2 were read from different snapshots?
> 
> Does the answer change if they were invoked on the same/different data 
> trees?
> 

If both reads target the same shard, they will be executed from the same 
snapshot.

Bye,
Robert

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