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<div class="moz-cite-prefix">I see 2 potential issues:<br>
<br>
1. How does the user know which node is the master to connect to,
since the operations are a no-op on all the others?<br>
<br>
- instead of a no-op, what if the other nodes just forward the
operation to the correct node?<br>
Then the user doesn't have to know who the current master
is, and can just connect to any node.<br>
<br>
2. What if the current master is one of the nodes being stopped?<br>
<br>
-Dennis<br>
<br>
On 05/31/2013 11:40 AM, Adrian Nistor wrote:<br>
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<div class="moz-cite-prefix">Yes, ISPN-1394 has a broader scope
but the proposed solution for ISPN-3140 solves quite a lot of
ISPN-1394 and it's not complex. We might not even need ISPN-1394
soon unless somebody really wants to control data ownership down
to segment granularity. If we only want to batch joins/leaves
and manually kick out nodes with or without loosing their data
then this proposal should be enough. This solution should not
prevent implementation of ISPN-1394 in future and will not need
to be removed/undone.<br>
<br>
Here are the details:<br>
<br>
1. <i>Add a JMX writable attribute (or operation?) to
ClusterTopologyManager (name it suppressRehashing?) that is
false by default but should also be configurable via API or
xml. While this attribute is true the ClusterTopologyManager
queues all join/leave/exclude(see below) requests and does not
execute them on the spot as it would normally happen. The
value of this attribute is ignored on all nodes but the
coordinator. When it is set back to false all queued
operations (except the ones that cancel eachother out) are
executed. The setter should be synchronous so when setting is
back to false it does not return until the queue is empty and
all rehashing was processed. </i><br>
<br>
2. <i>We add a JMX operation excludeNodes(list of addresses) to
ClusterTopologyManager. Calling this method on any node but
the coordinator is no-op. This operation removes the node from
the topology (almost as if it left) and forces a rebalance.</i>
The node is still present in the current CH but not in the
pending CH. It's basically disowned by all its data which is now
being transferred to other (not excluded) nodes. At the end of
the rebalance the node is removed from topology for good and can
be shut down without loosing data. Note that if
suppressRehashing==false operation excludeNodes(..) just queues
them for later removal. We can batch multiple such exclusions
and then re-activate the rehashing.<br>
<br>
The parts that need to be implemented are written in italic
above. Everything else is already there.<br>
<br>
excludeNodes is a way of achieving a soft shutdown and should be
used only if we care about preserving data int the extreme case
where the nodes are the last/single owners. We can just kill the
node directly if we do not care about its data. <br>
<br>
suppressRehashing is a way of achieving some kind of batching of
topology changes. This should speed up state transfer a lot
because it avoids a lot of pointless reshuffling of data
segments when we have many successive joiners/leavers.<br>
<br>
So what happens if the current coordinator dies for whatever
reason? The new one will take control and will not have
knowledge of the existing rehash queue or the previous status of
suppressRehashing attribute so it will just get the current
cache membership status from all members of current view and
proceed with the rehashing as usual. If the user does not want
this he can set a default value of true for suppressRehashing.
The admin has to interact now via JMX with the new coordinator.
But that's not as bad as the alternative where all the nodes are
involved in this jmx scheme :) I think having only the
coordinator involved in this is a plus.<br>
<br>
Manik, how does this fit for the full and partial shutdown?<br>
<br>
Cheers<br>
Adi<br>
<br>
<br>
On 05/31/2013 04:20 PM, Manik Surtani wrote:<br>
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cite="mid:BDFDAFF8-7620-49E5-9CAF-1B28DB795C78@redhat.com"
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<div>On 31 May 2013, at 13:52, Dan Berindei <<a
moz-do-not-send="true"
href="mailto:dan.berindei@gmail.com">dan.berindei@gmail.com</a>>
wrote:</div>
<br class="Apple-interchange-newline">
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<div>
<div>If we only want to deal with full cluster shutdown,
then I think stopping all application requests,
calling Cache.clear() on one node, and then shutting
down all the nodes should be simpler. On start,
assuming no cache store, the caches will start empty,
so starting all the nodes at once and only allowing
application requests when they've all joined should
also work without extra work.<br>
<br>
</div>
<div>If we only want to stop a part of the cluster,
suppressing rebalancing would be better, because we
wouldn't lose all the data. But we'd still lose the
keys whose owners are all among the nodes we want to
stop. I've discussed this with Adrian, and we think if
we want to stop a part of the cluster without losing
data we need a JMX operation on the coordinator that
will "atomically" remove a set of nodes from the CH.
After the operation completes, the user will know it's
safe to stop those nodes without losing data.<br>
</div>
</div>
</div>
</blockquote>
<div><br>
</div>
<div>I think the no-data-loss option is bigger scope, perhaps
part of ISPN-1394. And that's not what I am asking about.</div>
<br>
<blockquote type="cite">
<div dir="ltr">
<div>
<div>When it comes to starting a part of the cluster, a
"pause rebalancing" option would probably be better -
but again, on the coordinator, not on each joining
node. And clearly, if more than numOwner nodes leave
while rebalancing is suspended, data will be lost.</div>
</div>
</div>
</blockquote>
<div><br>
</div>
<div>Yup. This sort of option would only be used where data
loss isn't an issue (such as a distributed cache). Where
data loss is an issue, we'd need more control - ISPN-1394.</div>
<br>
<blockquote type="cite">
<div dir="ltr">
<div><br>
</div>
<div>Cheers<br>
</div>
<div>Dan<br>
<br>
</div>
</div>
<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On Fri, May 31, 2013 at 12:17 PM,
Manik Surtani <span dir="ltr"><<a
moz-do-not-send="true"
href="mailto:msurtani@redhat.com" target="_blank">msurtani@redhat.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">Guys<br>
<br>
We've discussed ISPN-3140 elsewhere before, I'm
brining it to this forum now.<br>
<br>
<a moz-do-not-send="true"
href="https://issues.jboss.org/browse/ISPN-3140"
target="_blank">https://issues.jboss.org/browse/ISPN-3140</a><br>
<br>
Any thoughts/concerns? Particularly looking to hear
from Dan or Adrian about viability, complexity, ease
of implementation.<br>
<br>
Thanks<br>
Manik<br>
--<br>
Manik Surtani<br>
<a moz-do-not-send="true"
href="mailto:manik@jboss.org">manik@jboss.org</a><br>
<a moz-do-not-send="true"
href="http://twitter.com/maniksurtani"
target="_blank">twitter.com/maniksurtani</a><br>
<br>
Platform Architect, JBoss Data Grid<br>
<a moz-do-not-send="true"
href="http://red.ht/data-grid" target="_blank">http://red.ht/data-grid</a><br>
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<div>Manik Surtani</div>
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