Well, I don't do SYNCHRONOUS_IGNORE_LEAVERS for commands that has less than
quorumSize number of destinations (so commands to single destination retain
it's ResponseMode unchanged) and recheck after the command that I still have
enough member in the cluster. But I will add a test to check that behaviour is
correct. I am not sure on the next sequence of events:
1) Node A locks key K with lock owner on node X
2) Node X dies
3) Lock ownership moves to node Y
4) Node B locks key K on Y
Best regards, Vitalii Tymchyshyn
________________________________
From: [email protected]
[mailto:[email protected]] On Behalf Of Dan Berindei
Sent: Thursday, June 06, 2013 5:09 AM
To: infinispan -Dev List
Subject: Re: [infinispan-dev] Using infinispan as quorum-based nosql
Say you have two transactions, tx1 and tx2. They both send a
LockControlCommand(k1) to the primary owner of k1 (let's call it B).
If the lock commands use SYNCHRONOUS_IGNORE_LEAVERS and B dies while processing
the commands, both tx1 and tx2 will think they have succeeded in locking k1.
So you're right, everything should be locked before prepare in pessimistic
mode, but LockControlCommands are also susceptible to SuspectExceptions. On the
other hand, you can use SYNCHRONOUS mode for LockControlCommands and you can
just retry the transaction in case of a SuspectException.
Unfortunately, you can't retry the transaction if the PrepareCommand fails (in
pessimistic mode; or the CommitCommand in optimistic mode), because it is
executed in the commit phase. The transaction manager swallows all the
exceptions in the commit phase, making it impossible to see if it failed
because of a node leaving. I guess this means I should increase the priority of
https://issues.jboss.org/browse/ISPN-2402 ...
On Thu, Jun 6, 2013 at 11:49 AM, <[email protected]> wrote:
Hello.
We are using pessimistic transaction mode. In this case everything's
already locked by the time of prepare, is not it?
As of merge, for quorum mode it's simple - take data from quorum. I
think I will try to simply suppress sending data from non-quorum members on
merge. Because currently everyone sends it's data and it creates complete mess
with unsynchronized data after merge (depending on the timing).
Best regards, Vitalii Tymchyshyn
________________________________
From: [email protected]
[mailto:[email protected]] On Behalf Of Dan Berindei
Sent: Wednesday, June 05, 2013 12:04 PM
To: infinispan -Dev List
Subject: Re: [infinispan-dev] Using infinispan as quorum-based nosql
On Mon, Jun 3, 2013 at 4:23 PM, <[email protected]> wrote:
Hello.
Thanks for your information. I will subscribe and vote for the
issues noted.
In the meantime I've implemented hacky JgroupsTransport that
"downgrades" all (but CacheViewControlCommand and StateTransferControlCommand)
SYNCHRONOUS invokeRemotely calls to SYNCHRONOUS_IGNORE_LEAVERS and checks if
required number of answers was received with a filter (I've tried to use
original invokeRemotely return value but it often returns some strange value,
like empty map). It seems to do the trick for me. But I am still not sure if
this has any side effects.
Indeed, I started working on a solution, but I over-engineered it and
then I got side-tracked with other stuff. Sorry about that.
The problem with using SYNCHRONOUS_IGNORE_LEAVERS everywhere, as I
found out, is that you don't want to ignore the primary owner of a key leaving
during a prepare/lock command (or the coordinator, in REPL mode prior to
5.3.0.CR1/ISPN-2772). If that happens, you have to retry on the new primary
owner, otherwise you can't know if the prepare command has locked the key or
not.
A similar problem appears in non-transactional caches with
supportsConcurrentUpdates=true: there the primary owner can ignore any of the
backup owners leaving, but the originator can't ignore the primary owner
leaving.
For now I can see merge problem in my test: different values
are picked during merge. I am going to dig a little deeper and follow up. But
it's already a little strange for me, since the test algorithm is:
1)Assign "old" value to full cluster (it's REPL_SYNC mode)
2)Block coordinator
3)Writer "new" value to one of two remaining nodes. It's
syncrhonized to second remaining node
4)Unblock coordinator
5)Wait (I could not find a good way to wait for state transfer
but wait in this case).
6)Check the value on coordinator
And in my test I am randomly getting "old" or "new" in assert.
I am now going to check why. May be I will need to "reinitialize" smaller
cluster part to ensure data is taken from the quorum part of the cluster.
We don't handle merges properly. See
https://issues.jboss.org/browse/ISPN-263 and the discussion at
http://markmail.org/message/meyczotzobuva7js
What happens right now is that after a merge, all the caches are
assumed to have up-to-date data, so there is no state transfer. We had several
ideas floating around on how we could force the smaller partition to receive
data from the quorum partition, but I think with the public API your best
option is to stop all the caches in the smaller partition after the split and
start them back up after the merge.
Cheers
Dan
Best regards, Vitalii Tymchyshyn
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Galder Zamarreno
Sent: Monday, June 03, 2013 9:04 AM
To: infinispan -Dev List
Subject: Re: [infinispan-dev] Using infinispan as quorum-based
nosql
On May 30, 2013, at 5:10 PM, [email protected] wrote:
> Hello.
>
> We are going to use Infinispan in our project as NoSQL
solution. It
> performs quite well for us, but currently we've faced next
problem.
> Note: We are using Infinispan 5.1.6 in SYNC_REPL mode in
small cluster.
> The problem is that when any node fails, any running
transactions wait
> for Jgroups to decide if it've really failed or not and
rollback
> because of SuspectException after that. While we can live
with a
> delay, we'd really like to skip rolling back. As for me, I
actually
> don't see a reason for rollback because transactions started
after
> leave will succeed. So, as for me, previously running
transactions
> could do the same.
We're aware of the problem
(https://issues.jboss.org/browse/ISPN-2402).
@Dan, has there been any updates on this?
> The question for is if node that left will synchronize it's
state
> after merge (even if merge was done without infinispan
restart). As
> for me, it should or it won't work correctly at all.
This is not in yet: https://issues.jboss.org/browse/ISPN-263
> So, I've found RpcManager's
ResponseMode.SYNCHRONOUS_IGNORE_LEAVERS
> and think on switching to it for RpcManager calls that don't
specify
> ResponseMode explicitly. As for me, it should do the trick.
Also, I am
> going to enforce Quorum number of reponses, but that's
another story.
> So, how do you think, would it work?
^ Not sure if that'll work. @Dan?
> P.S. Another Q for me, how does it work now, when
SuspectException is
> thrown from CommitCommand broadcasting. Af far as I can see,
commit is
> still done on some remote nodes (that are still in the
cluster), but
> rolled back on local node because of this exception. Am I
correct?
^ How Infinispan reacts in these situations depends a lot on
the type of communications (synchronous or asynchronous) and the transaction
configuration. Mircea can provide more details on this.
Cheers,
> This
> can cause inconsistencies, but we must leave with something in
> peer-to-peer world :) The only other option is to switch from
> write-all, read-local to write-quorum, read-quorum scenario
that is
> too complex move for Infinispan as for me.
>
> Best regards, Vitalii Tymchyshyn
>
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--
Galder Zamarreño
[email protected]
twitter.com/galderz
Project Lead, Escalante
http://escalante.io
Engineer, Infinispan
http://infinispan.org
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