9:02 a.m.
Hi,
I've starte a document[1] that contains 3 possible approaches for implementing the
X-datacentre replication functionality.
This is a highly requested bit of functionality for 5.2 and involves interaction between
several components: e.g. state transfer, transactions hotrod, jgroups etc. Can you please
take a look and comment?
[1] https://community.jboss.org/wiki/CrossDatacenterReplication-Design
Cheers
Mircea
--
Mircea Markus
twitter.com/mirceamarkus
Sr. Software Engineer, Infinispan
http://www.infinispan.org
9:47 a.m.
I'm going to comment via this mailing list, and we can later summarize
and append to the wiki (I don't like discussions on the wiki... :-))...
#1 Virtual cluster
Rehashing:
I believe we'll have to come up with a custom consistent hash that knows
about the 2 sites, and places all of the data owners into the local
site. E.g. it would be bad if we create a key K in LON and make the
primary owner T (in SFO) and the backup owner B in LON !
This should also minimize rehashing across sites, and prefer rehashing
within sites.
In terms of data access, the idea is that all writes would only go
through 1 site, e.g. LON being active and SFO being a backup (in which
reads could happen); my design didn't assume concurrent writes in
multiple sites (at least not to the same data).
Locking:
Same as above
Configuration:
numOwners would have to be extended, e.g. we could introduce a property
numPrimarySiteOwners=2 and numBackupSiteOwners=1, TDB
#2 Hot Rod based
Having to connect to potentially all nodes is bad, as customers possibly
only want to open 1 port for cross-datacenter traffic.
I assume the RemoteCacheStore would have to be enabled in all nodes in a
given site for this to work ?
How would you handle requests sent during the crash of a HotRod endpoint
? Would they get queued, similar to
https://issues.jboss.org/browse/JGRP-1401 ?
How would initial state transfer be done between sites ? E.g. LON has
been up for 2 days and now we start SFO. Does that mean we will
effectively have to transfer *all* of the data in LON --> SFO ?
#3 Custom bridge
I like the fact that both sites are configured with possibly different
numOwners, e.g. LON=2 and SFO=1
This will not work if you need to invoke blocking RPCs between sites:
the copying of traffic to A is always assumed to be asynchronous. Plus,
the recipient in SFO wouldn't know the original sender; in the example,
the sender would always be X.
How do you handle the case where the relay (A or X) crashes and messages
are sent during that time, before a new relay is elected ?
How do you do state transfer, e.g. bootstrap SFO from LON ? I guess you
transfer the entire state from LON --> SFO, right ?
SUMMARY:
I would definitely *not* do #2.
I do like #3 and #1, perhaps we need to focus a bit on #3, to see if
there are other deficiencies we haven't seen yet, as I'm already
familiar with #1.
Cheers,
On 2/10/12 4:02 PM, Mircea Markus wrote:
Hi,
I've starte a document[1] that contains 3 possible approaches for implementing the
X-datacentre replication functionality.
This is a highly requested bit of functionality for 5.2 and involves interaction between
several components: e.g. state transfer, transactions hotrod, jgroups etc. Can you please
take a look and comment?
[1] https://community.jboss.org/wiki/CrossDatacenterReplication-Design
--
Bela Ban
Lead JGroups (http://www.jgroups.org)
JBoss / Red Hat
1:17 p.m.
Hi Mircea
I think you're missing an intro section with the use cases we want to
handle in 5.2.
The requirements for having a backup datacenter that isn't accessed by
any clients are pretty different from the requirements for multiple
"primary" datacenters that are all handling requests at the same time,
so we should have a clear image of what we are trying to achieve.
On Fri, Feb 10, 2012 at 5:47 PM, Bela Ban <bban(a)redhat.com> wrote:
I'm going to comment via this mailing list, and we can later
summarize
and append to the wiki (I don't like discussions on the wiki... :-))...
#1 Virtual cluster
Rehashing:
I believe we'll have to come up with a custom consistent hash that knows
about the 2 sites, and places all of the data owners into the local
site. E.g. it would be bad if we create a key K in LON and make the
primary owner T (in SFO) and the backup owner B in LON !
This should also minimize rehashing across sites, and prefer rehashing
within sites.
For some use cases I would think it's essential that the data is
replicated in both sites (async, of course).
But I second the idea that there must be at least one backup in the
same site as the primary owner, or rehashes become really expensive.
In terms of data access, the idea is that all writes would only go
through 1 site, e.g. LON being active and SFO being a backup (in which
reads could happen); my design didn't assume concurrent writes in
multiple sites (at least not to the same data).
I like the idea of designating one site as the "master", but I'm
pretty sure we want to handle use cases where there is more than one
master.
Perhaps we could incorporate Erik's suggestion on the wiki and allow
the selection of a master site both at a cache level and at a key
level.
Locking:
Same as above
Having only one master site would certainly make locking easier.
In the other scenarios I'm not sure if we should always designate a
master site for a key and always lock there, or if we should only lock
on a "local primary owner" that's in the same site as the transaction
originator.
Configuration:
numOwners would have to be extended, e.g. we could introduce a property
numPrimarySiteOwners=2 and numBackupSiteOwners=1, TDB
Should we allow the user to specify the number of backup sites as
well? That's assuming we are going to support more than two sites...
#2 Hot Rod based
Having to connect to potentially all nodes is bad, as customers possibly
only want to open 1 port for cross-datacenter traffic.
I'm not sure I agree. It would be bad if we expect to connect over the
internet to the remote site, but I assume that everyone would use a
VPN to communicate between sites anyway.
I assume the RemoteCacheStore would have to be enabled in all nodes
in a
given site for this to work ?
How would you handle requests sent during the crash of a HotRod endpoint
? Would they get queued, similar to
https://issues.jboss.org/browse/JGRP-1401 ?
How would initial state transfer be done between sites ? E.g. LON has
been up for 2 days and now we start SFO. Does that mean we will
effectively have to transfer *all* of the data in LON --> SFO ?
#3 Custom bridge
I like the fact that both sites are configured with possibly different
numOwners, e.g. LON=2 and SFO=1
+1
This will not work if you need to invoke blocking RPCs between
sites:
the copying of traffic to A is always assumed to be asynchronous. Plus,
the recipient in SFO wouldn't know the original sender; in the example,
the sender would always be X.
Mircea was saying that we'd only send over committed modifications, so
no locking RPCs that need to be synchronous.
I'm not sure if the original sender is still relevant in this case.
How do you handle the case where the relay (A or X) crashes and
messages
are sent during that time, before a new relay is elected ?
I suspect this one is the tricky bit... Mircea did mention that he'd
like to reuse the retransmission logic from RELAY, but I'm not sure
how easy that would be.
How do you do state transfer, e.g. bootstrap SFO from LON ? I guess
you
transfer the entire state from LON --> SFO, right ?
For 5.2 I think this would be acceptable.
SUMMARY:
I would definitely *not* do #2.
I do like #3 and #1, perhaps we need to focus a bit on #3, to see if
there are other deficiencies we haven't seen yet, as I'm already
familiar with #1.
Cheers,
On 2/10/12 4:02 PM, Mircea Markus wrote:
> Hi,
>
> I've starte a document[1] that contains 3 possible approaches for implementing
the X-datacentre replication functionality.
> This is a highly requested bit of functionality for 5.2 and involves interaction
between several components: e.g. state transfer, transactions hotrod, jgroups etc. Can you
please take a look and comment?
>
> [1] https://community.jboss.org/wiki/CrossDatacenterReplication-Design
--
Bela Ban
Lead JGroups (http://www.jgroups.org)
JBoss / Red Hat
_______________________________________________
infinispan-dev mailing list
infinispan-dev(a)lists.jboss.org
https://lists.jboss.org/mailman/listinfo/infinispan-dev
1:21 p.m.
Hi Mircea
I think you're missing an intro section with the use cases we want to
handle in 5.2.
The requirements for having a backup datacenter that isn't accessed
by
any clients are pretty different from the requirements for multiple
"primary" datacenters that are all handling requests at the same
time,
so we should have a clear image of what we are trying to achieve.
+1. That becabe very clear after reading Bela's email :-)
On Fri, Feb 10, 2012 at 5:47 PM, Bela Ban <bban(a)redhat.com> wrote:
> I'm going to comment via this mailing list, and we can later
> summarize
> and append to the wiki (I don't like discussions on the wiki...
> :-))...
>
> #1 Virtual cluster
>
> Rehashing:
>
> I believe we'll have to come up with a custom consistent hash that
> knows
> about the 2 sites, and places all of the data owners into the local
> site. E.g. it would be bad if we create a key K in LON and make the
> primary owner T (in SFO) and the backup owner B in LON !
> This should also minimize rehashing across sites, and prefer
> rehashing
> within sites.
>
For some use cases I would think it's essential that the data is
replicated in both sites (async, of course).
But I second the idea that there must be at least one backup in the
same site as the primary owner, or rehashes become really expensive.
+1. Or rehash
can be inproved to send statet only if the joiner is colocated (vs send state if node is
primary owner).
> In terms of data access, the idea is that all writes would only go
> through 1 site, e.g. LON being active and SFO being a backup (in
> which
> reads could happen); my design didn't assume concurrent writes in
> multiple sites (at least not to the same data).
+1. I'll make that clearer
in the doc as well.
>
I like the idea of designating one site as the "master", but I'm
pretty sure we want to handle use cases where there is more than one
master.
+1
Perhaps we could incorporate Erik's suggestion on the wiki and
allow
the selection of a master site both at a cache level and at a key
level.
+1
Thanks Dan!
2:06 a.m.
On 10 February 2012 19:17, Dan Berindei <dan.berindei(a)gmail.com> wrote:
Mircea was saying that we'd only send over committed
modifications, so
no locking RPCs that need to be synchronous.
I understand the performance cost would be otherwise high, but is this
not defeating the purpose?
I would expect as a user that - if I need cross-datacenter replication
- I would get a strong guarantee that committed data is safe in both
locations, not that some might still need to be sent.
So I would expect that - for transactional operations only - the other
locations participate in the prepare phase.
If we go for async replication, won't we need as well some way to
guarantee that the other replicas apply changes in the correct order?
About the cons in #3, it states
"the state transfer needs to be customized to send all cluster's state
through the end-point."
Why? Can't we have each node connect directly? No endpoint -> no overloading.
If you think of it as an async cachestore, you would have each entry
managed by it's primary owner and possibly sent directly to the right
target (assuming routers and VPNs are transparent to our logic).
5:07 a.m.
----- Original Message -----
From: "Sanne Grinovero" <sanne(a)infinispan.org>
To: "infinispan -Dev List" <infinispan-dev(a)lists.jboss.org>
Sent: Monday, February 13, 2012 8:06:03 AM
Subject: Re: [infinispan-dev] X-datacentre replication: design suggestions
On 10 February 2012 19:17, Dan Berindei <dan.berindei(a)gmail.com>
wrote:
> Mircea was saying that we'd only send over committed modifications,
> so
> no locking RPCs that need to be synchronous.
I understand the performance cost would be otherwise high, but is
this
not defeating the purpose?
I would expect as a user that - if I need cross-datacenter
replication
- I would get a strong guarantee that committed data is safe in both
locations, not that some might still need to be sent.
If you configure an *sync*
bridge then you'd get the confirmation during the commit. What you don't get by
participating in the preapre is consistency guarnatees for two tx writing to same data in
different datacenters - but not sure we want to support that?
So I would expect that - for transactional operations only - the
other
locations participate in the prepare phase.
If we go for async replication, won't we need as well some way to
guarantee that the other replicas apply changes in the correct order?
Can you
please detail on this scenario?
About the cons in #3, it states
"the state transfer needs to be customized to send all cluster's
state
through the end-point."
Why? Can't we have each node connect directly? No endpoint -> no
overloading.
that's what #2 does. Possible, but it has its cons, mainly the
number of x-site connections. See bela's comment in a previous email and Erik's
comment here: https://community.jboss.org/wiki/CrossDatacenterReplication-Design
5:22 a.m.
On 13 February 2012 11:07, Mircea Markus <mmarkus(a)redhat.com> wrote:
----- Original Message -----
> From: "Sanne Grinovero" <sanne(a)infinispan.org>
> To: "infinispan -Dev List" <infinispan-dev(a)lists.jboss.org>
> Sent: Monday, February 13, 2012 8:06:03 AM
> Subject: Re: [infinispan-dev] X-datacentre replication: design suggestions
>
> On 10 February 2012 19:17, Dan Berindei <dan.berindei(a)gmail.com>
> wrote:
> > Mircea was saying that we'd only send over committed modifications,
> > so
> > no locking RPCs that need to be synchronous.
>
> I understand the performance cost would be otherwise high, but is
> this
> not defeating the purpose?
> I would expect as a user that - if I need cross-datacenter
> replication
> - I would get a strong guarantee that committed data is safe in both
> locations, not that some might still need to be sent.
If you configure an *sync* bridge then you'd get the confirmation during the commit.
What you don't get by participating in the preapre is consistency guarnatees for two
tx writing to same data in different datacenters - but not sure we want to support that?
> So I would expect that - for transactional operations only - the
> other
> locations participate in the prepare phase.
> If we go for async replication, won't we need as well some way to
> guarantee that the other replicas apply changes in the correct order?
Can you please detail on this scenario?
I have two transactions, run in sequence:
- TX1 updates A
- TX2 deletes A
If you send them both in async to the other datacenter, you'll have to
make sure they are not reordered. I know JGroups can provide that
guarantee, just wondering if it's the plan to do this via JGroups, or
if we have an own buffer that we can still guarantee the order, or
even better merge changes on the same keys like we do with the async
CacheStore.
6:49 a.m.
On 2/13/12 12:22 PM, Sanne Grinovero wrote:
I have two transactions, run in sequence:
- TX1 updates A
- TX2 deletes A
If you send them both in async to the other datacenter, you'll have to
make sure they are not reordered. I know JGroups can provide that
guarantee, just wondering if it's the plan to do this via JGroups, or
if we have an own buffer that we can still guarantee the order, or
even better merge changes on the same keys like we do with the async CacheStore.
This use case cannot be supported by option #3 AFAICS: the bridge
between LON and SFO is completely asynchronous and doesn't know anything
about sync or async RPCs, so TX2 can be applied in SFO before TX1.
With option #2, if you run with SYNC, then the TX1 will complete before
TX2 is started. Unless, of course, the 2 transactions are started on
different nodes: then, it depends on which TX acquires the locks first,
but this is the same behavior as in a local cluster.
Hmm, how does option #3 handle TXs anyway ? Does a PUT on B and C not
trigger anything until the TX has been completed successfully, and then
we forward the outcome of the TX to A, which forwards it to X ? How does
X then apply it ? Special operation or a set of PUT and REMOVES ?
--
Bela Ban
Lead JGroups (http://www.jgroups.org)
JBoss / Red Hat
7:59 a.m.
On 13 Feb 2012, at 12:49, Bela Ban wrote:
Hmm, how does option #3 handle TXs anyway ? Does a PUT on B and C not
trigger anything until the TX has been completed successfully, and then
we forward the outcome of the TX to A, which forwards it to X ? How does
X then apply it ? Special operation or a set of PUT and REMOVES ?
Well, the PrepareCommand contains a collection of WriteCommands… so this would be pushed
to the next DC.
--
Manik Surtani
manik(a)jboss.org
twitter.com/maniksurtani
Lead, Infinispan
http://www.infinispan.org
9:21 a.m.
On Mon, Feb 13, 2012 at 2:49 PM, Bela Ban <bban(a)redhat.com> wrote:
On 2/13/12 12:22 PM, Sanne Grinovero wrote:
> I have two transactions, run in sequence:
> - TX1 updates A
> - TX2 deletes A
>
> If you send them both in async to the other datacenter, you'll have to
> make sure they are not reordered. I know JGroups can provide that
> guarantee, just wondering if it's the plan to do this via JGroups, or
> if we have an own buffer that we can still guarantee the order, or
> even better merge changes on the same keys like we do with the async CacheStore.
This use case cannot be supported by option #3 AFAICS: the bridge
between LON and SFO is completely asynchronous and doesn't know anything
about sync or async RPCs, so TX2 can be applied in SFO before TX1.
With option #2, if you run with SYNC, then the TX1 will complete before
TX2 is started. Unless, of course, the 2 transactions are started on
different nodes: then, it depends on which TX acquires the locks first,
but this is the same behavior as in a local cluster.
Not if we use the RemoteCacheStore... A cache store is only called
during commit + HotRod doesn't support transactions.
So I believe option #2 can also support only async replication between sites.
9:59 a.m.
----- Original Message -----
From: "Bela Ban" <bban(a)redhat.com>
To: infinispan-dev(a)lists.jboss.org
Sent: Monday, February 13, 2012 12:49:56 PM
Subject: Re: [infinispan-dev] X-datacentre replication: design suggestions
On 2/13/12 12:22 PM, Sanne Grinovero wrote:
> I have two transactions, run in sequence:
> - TX1 updates A
> - TX2 deletes A
>
> If you send them both in async to the other datacenter, you'll have
> to
> make sure they are not reordered. I know JGroups can provide that
> guarantee, just wondering if it's the plan to do this via JGroups,
> or
> if we have an own buffer that we can still guarantee the order, or
> even better merge changes on the same keys like we do with the
> async CacheStore.
This use case cannot be supported by option #3 AFAICS: the bridge
between LON and SFO is completely asynchronous and doesn't know
anything
about sync or async RPCs, so TX2 can be applied in SFO before TX1.
Why can't
the bridge send the messages in the order in which they were enqueued?
With option #2, if you run with SYNC, then the TX1 will complete
before
TX2 is started. Unless, of course, the 2 transactions are started on
different nodes: then, it depends on which TX acquires the locks
first,
but this is the same behavior as in a local cluster.
Hmm, how does option #3 handle TXs anyway ? Does a PUT on B and C not
trigger anything until the TX has been completed successfully, and
then
we forward the outcome of the TX to A, which forwards it to X ?
That's what i
have in mind.
How does
X then apply it ? Special operation or a set of PUT and REMOVES ?
The simplest
approach is for X to starts a tx, run all the ops and commit it. A more advanced apprach
is for X to determine, based on the key set, which scenarios node is the most appropriate
to run the tx and delegate run of the transaction to the given node. Actually the second
approch can be easily implemented through a distriuted executor.
10:15 a.m.
On 2/13/12 4:59 PM, Mircea Markus wrote:
> This use case cannot be supported by option #3 AFAICS: the
bridge
> between LON and SFO is completely asynchronous and doesn't know
> anything
> about sync or async RPCs, so TX2 can be applied in SFO before TX1.
Why can't the bridge send the messages in the order in which they were enqueued?
It *does* deliver the messages in the order in which they were sent. I
was referring to the async case in general: commits from different nodes
hit the bridge in an undefined order; in your example it could be TX1
--> TX2 or TX2 --> TX1.
(Note that I mixed up option #2 and option #1 in my previous email)
--
Bela Ban
Lead JGroups (http://www.jgroups.org)
JBoss / Red Hat
9:48 a.m.
I have two transactions, run in sequence:
- TX1 updates A
- TX2 deletes A
If you send them both in async to the other datacenter, you'll have
to
make sure they are not reordered. I know JGroups can provide that
guarantee, just wondering if it's the plan to do this via JGroups, or
if we have an own buffer that we can still guarantee the order, or
even better merge changes on the same keys like we do with the async
CacheStore.
Thanks for the clarification, Sanne.
Tx1 needs to place the info into the bridge's async queue *before* releasing the lock.
Commit is a good fit, as durign commit the lock is stil held. Then the bridge must make
sure that it doesn't reorder elements in the queue.
1:18 p.m.
#1 Virtual cluster
Rehashing:
I believe we'll have to come up with a custom consistent hash that
knows
about the 2 sites, and places all of the data owners into the local
site. E.g. it would be bad if we create a key K in LON and make the
primary owner T (in SFO) and the backup owner B in LON !
I think this approach works very well if you use SFO as an hot-standby for LON: the
purpose of SFO bein is to pick up the load in the case LON goes down for whatever reason.
In an follow the sun approach, in which LON is up for 12h and then SFO takes over the next
12h there's this won't work.
This should also minimize rehashing across sites, and prefer
rehashing
within sites.
Not sure about that: AFAIK the way rehashing is implemented, is always the primary owner
that generates the state. So if the joiner is in SFO then the burden of join would be much
higher.
In terms of data access, the idea is that all writes would only go
through 1 site, e.g. LON being active and SFO being a backup (in
which
reads could happen); my design didn't assume concurrent writes in
multiple sites (at least not to the same data).
Yes indeed this would work for the master-slave (or hot standby scenario). IMO we should
also consider the master-master (follow the sun) approach as well.
Locking:
Same as above
Configuration:
numOwners would have to be extended, e.g. we could introduce a
property
numPrimarySiteOwners=2 and numBackupSiteOwners=1, TDB
yes indeed these attributes
would be specific to the new CH function you added.
#2 Hot Rod based
Having to connect to potentially all nodes is bad, as customers
possibly
only want to open 1 port for cross-datacenter traffic.
+1.
I assume the RemoteCacheStore would have to be enabled in all nodes
in a
given site for this to work ?
yes. that's a cons for this approach.
How would you handle requests sent during the crash of a HotRod
endpoint
? Would they get queued, similar to
https://issues.jboss.org/browse/JGRP-1401 ?
that would need to be re-implemented indeed. It's the first in the list of cons for
this approach.
How would initial state transfer be done between sites ? E.g. LON has
been up for 2 days and now we start SFO. Does that mean we will
effectively have to transfer *all* of the data in LON --> SFO ?
Transfering all the data is required as the data must be mirrored between the sites.
Of course we'll onloy transfer every entry once, and not numOwners times.
#3 Custom bridge
I like the fact that both sites are configured with possibly
different
numOwners, e.g. LON=2 and SFO=1
This will not work if you need to invoke blocking RPCs between sites:
the copying of traffic to A is always assumed to be asynchronous.
Why that? async
replication is intended as a default, but sync replication should be possible as well.
Just that the bridge would make the invocation in a synchronious way.
Plus,
the recipient in SFO wouldn't know the original sender; in the
example,
the sender would always be X.
Not sure why this is bad for a functional perspective. As long as the sites end up being
in sync.
How do you handle the case where the relay (A or X) crashes and
messages
are sent during that time, before a new relay is elected ?
A subset of RELAY can be
used for this, together with JGRP-1401.
How do you do state transfer, e.g. bootstrap SFO from LON ? I guess
you
transfer the entire state from LON --> SFO, right ?
Indeed state transfer seems to be the biggest challange with this approach. I have some
ideas, I'd also like to get Dan's input on this.
SUMMARY:
I would definitely *not* do #2.
+1
I do like #3 and #1, perhaps we need to focus a bit on #3, to see if
there are other deficiencies we haven't seen yet, as I'm already
familiar with #1.
thanks bela!
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13 comments
5 participants
participants (5)
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Bela Ban -
Dan Berindei -
Manik Surtani -
Mircea Markus -
Sanne Grinovero