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From Rafael Weingärtner <rafaelweingart...@gmail.com>
Subject Re: [Discuss] Management cluster / Zookeeper holding locks
Date Mon, 18 Dec 2017 12:10:27 GMT
So, we would need to change every piece of code that opens and uses
connections and transactions to change to ZK model? I mean, to direct the
flow to ZK.

On Mon, Dec 18, 2017 at 8:55 AM, Marc-Aurèle Brothier <marco@exoscale.ch>
wrote:

> I understand your point, but there isn't any "transaction" in ZK. The
> transaction and commit stuff are really for DB and not part of ZK. All
> entries (if you start writing data in some nodes) are versioned. For
> example you could enforce that to overwrite a node value you must submit
> the node data having the same last version id to ensure you were
> overwriting from the latest value/state of that node. Bear in mind that you
> should not put too much data into your ZK, it's not a database replacement,
> neither a nosql db.
>
> The ZK client (CuratorFramework object) is started on the server startup,
> and you only need to pass it along your calls so that the connection is
> reused, or retried, depending on the state. Nothing manual has to be done,
> it's all in this curator library.
>
> On Mon, Dec 18, 2017 at 11:44 AM, Rafael Weingärtner <
> rafaelweingartner@gmail.com> wrote:
>
> > I did not check the link before. Sorry about that.
> >
> > Reading some of the pages there, I see curator more like a client library
> > such as MySQL JDBC client.
> >
> > When I mentioned framework, I was looking for something like Spring-data.
> > So, we could simply rely on the framework to manage connections and
> > transactions. For instance, we could define a pattern that would open
> > connection with a read-only transaction. And then, we could annotate
> > methods that would write in the database something with
> > @Transactional(readonly = false). If we are going to a change like this
> we
> > need to remove manually open connections and transactions. Also, we have
> to
> > remove the transaction management code from our code base.
> >
> > I would like to see something like this [1] in our future. No manually
> > written transaction code, and no transaction management in our code base.
> > Just simple annotation usage or transaction pattern in Spring XML files.
> >
> > [1]
> > https://github.com/rafaelweingartner/daily-tasks/
> > blob/master/src/main/java/br/com/supero/desafio/services/
> TaskService.java
> >
> > On Mon, Dec 18, 2017 at 8:32 AM, Marc-Aurèle Brothier <marco@exoscale.ch
> >
> > wrote:
> >
> > > @rafael, yes there is a framework (curator), it's the link I posted in
> my
> > > first message: https://curator.apache.org/curator-recipes/shared-lock.
> > html
> > > This framework helps handling all the complexity of ZK.
> > >
> > > The ZK client stays connected all the time (as the DB connection pool),
> > and
> > > only one connection (ZKClient) is needed to communicate with the ZK
> > server.
> > > The framework handles reconnection as well.
> > >
> > > Have a look at ehc curator website to understand its goal:
> > > https://curator.apache.org/
> > >
> > > On Mon, Dec 18, 2017 at 11:01 AM, Rafael Weingärtner <
> > > rafaelweingartner@gmail.com> wrote:
> > >
> > > > Do we have framework to do this kind of looking in ZK?
> > > > I mean, you said " create a new InterProcessSemaphoreMutex which
> > handles
> > > > the locking mechanism.". This feels that we would have to continue
> > > opening
> > > > and closing this transaction manually, which is what causes a lot of
> > our
> > > > headaches with transactions (it is not MySQL locks fault entirely,
> but
> > > our
> > > > code structure).
> > > >
> > > > On Mon, Dec 18, 2017 at 7:47 AM, Marc-Aurèle Brothier <
> > marco@exoscale.ch
> > > >
> > > > wrote:
> > > >
> > > > > We added ZK lock for fix this issue but we will remove all current
> > > locks
> > > > in
> > > > > ZK in favor of ZK one. The ZK lock is already encapsulated in a
> > project
> > > > > with an interface, but more work should be done to have a proper
> > > > interface
> > > > > for locks which could be implemented with the "tool" you want,
> > either a
> > > > DB
> > > > > lock for simplicity, or ZK for more advanced scenarios.
> > > > >
> > > > > @Daan you will need to add the ZK libraries in CS and have a
> running
> > ZK
> > > > > server somewhere. The configuration value is read from the
> > > > > server.properties. If the line is empty, the ZK client is not
> created
> > > and
> > > > > any lock request will immediately return (not holding any lock).
> > > > >
> > > > > @Rafael: ZK is pretty easy to setup and have running, as long as
> you
> > > > don't
> > > > > put too much data in it. Regarding our scenario here, with only
> > locks,
> > > > it's
> > > > > easy. ZK would be only the gatekeeper to locks in the code,
> ensuring
> > > that
> > > > > multi JVM can request a true lock.
> > > > > For the code point of view, you're opening a connection to a ZK
> node
> > > (any
> > > > > of a cluster) and you create a new InterProcessSemaphoreMutex which
> > > > handles
> > > > > the locking mechanism.
> > > > >
> > > > > On Mon, Dec 18, 2017 at 10:24 AM, Ivan Kudryavtsev <
> > > > > kudryavtsev_ia@bw-sw.com
> > > > > > wrote:
> > > > >
> > > > > > Rafael,
> > > > > >
> > > > > > - It's easy to configure and run ZK either in single node or
> > cluster
> > > > > > - zookeeper should replace mysql locking mechanism used inside
> ACS
> > > code
> > > > > > (places where ACS locks tables or rows).
> > > > > >
> > > > > > I don't think from the other size, that moving from MySQL locks
> to
> > ZK
> > > > > locks
> > > > > > is easy and light and (even implemetable) way.
> > > > > >
> > > > > > 2017-12-18 16:20 GMT+07:00 Rafael Weingärtner <
> > > > > rafaelweingartner@gmail.com
> > > > > > >:
> > > > > >
> > > > > > > How hard is it to configure Zookeeper and get everything
up and
> > > > > running?
> > > > > > > BTW: what zookeeper would be managing? CloudStack management
> > > servers
> > > > or
> > > > > > > MySQL nodes?
> > > > > > >
> > > > > > > On Mon, Dec 18, 2017 at 7:13 AM, Ivan Kudryavtsev <
> > > > > > > kudryavtsev_ia@bw-sw.com>
> > > > > > > wrote:
> > > > > > >
> > > > > > > > Hello, Marc-Aurele, I strongly believe that all mysql
locks
> > > should
> > > > be
> > > > > > > > removed in favour of truly DLM solution like Zookeeper.
The
> > > > > performance
> > > > > > > of
> > > > > > > > 3node ZK ensemble should be enough to hold up to 1000-2000
> > locks
> > > > per
> > > > > > > second
> > > > > > > > and it helps to move to truly clustered MySQL like
galera
> > without
> > > > > > single
> > > > > > > > master server.
> > > > > > > >
> > > > > > > > 2017-12-18 15:33 GMT+07:00 Marc-Aurèle Brothier <
> > > marco@exoscale.ch
> > > > >:
> > > > > > > >
> > > > > > > > > Hi everyone,
> > > > > > > > >
> > > > > > > > > I was wondering how many of you are running CloudStack
> with a
> > > > > cluster
> > > > > > > of
> > > > > > > > > management servers. I would think most of you,
but it would
> > be
> > > > nice
> > > > > > to
> > > > > > > > hear
> > > > > > > > > everyone voices. And do you get hosts going over
their
> > capacity
> > > > > > limits?
> > > > > > > > >
> > > > > > > > > We discovered that during the VM allocation,
if you get a
> lot
> > > of
> > > > > > > parallel
> > > > > > > > > requests to create new VMs, most notably with
large
> profiles,
> > > the
> > > > > > > > capacity
> > > > > > > > > increase is done too far after the host capacity
checks and
> > > > results
> > > > > > in
> > > > > > > > > hosts going over their capacity limits. To detail
the
> steps:
> > > the
> > > > > > > > deployment
> > > > > > > > > planner checks for cluster/host capacity and
pick up one
> > > > deployment
> > > > > > > plan
> > > > > > > > > (zone, cluster, host). The plan is stored in
the database
> > > under a
> > > > > > > VMwork
> > > > > > > > > job and another thread picks that entry and starts
the
> > > > deployment,
> > > > > > > > > increasing the host capacity and sending the
commands. Here
> > > > > there's a
> > > > > > > > time
> > > > > > > > > gap between the host being picked up and the
capacity
> > increase
> > > > for
> > > > > > that
> > > > > > > > > host of a couple of seconds, which is well enough
to go
> over
> > > the
> > > > > > > capacity
> > > > > > > > > on one or more hosts. A few VMwork job can be
added in the
> DB
> > > > queue
> > > > > > > > > targeting the same host before one gets picked
up.
> > > > > > > > >
> > > > > > > > > To fix this issue, we're using Zookeeper to act
as the
> multi
> > > JVM
> > > > > lock
> > > > > > > > > manager thanks to their curator library (
> > > > > > > > > https://curator.apache.org/curator-recipes/shared-lock.
> html
> > ).
> > > We
> > > > > > also
> > > > > > > > > changed the time when the capacity is increased,
which
> occurs
> > > now
> > > > > > > pretty
> > > > > > > > > much after the deployment plan is found and inside
the
> > > zookeeper
> > > > > > lock.
> > > > > > > > This
> > > > > > > > > ensure we don't go over the capacity of any host,
and it
> has
> > > been
> > > > > > > proven
> > > > > > > > > efficient since a month in our management server
cluster.
> > > > > > > > >
> > > > > > > > > This adds another potential requirement which
should be
> > discuss
> > > > > > before
> > > > > > > > > proposing a PR. Today the code works seamlessly
without ZK
> > too,
> > > > to
> > > > > > > ensure
> > > > > > > > > it's not a hard requirement, for example in a
lab.
> > > > > > > > >
> > > > > > > > > Comments?
> > > > > > > > >
> > > > > > > > > Kind regards,
> > > > > > > > > Marc-Aurèle
> > > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > > --
> > > > > > > > With best regards, Ivan Kudryavtsev
> > > > > > > > Bitworks Software, Ltd.
> > > > > > > > Cell: +7-923-414-1515
> > > > > > > > WWW: http://bitworks.software/ <http://bw-sw.com/>
> > > > > > > >
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > --
> > > > > > > Rafael Weingärtner
> > > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > --
> > > > > > With best regards, Ivan Kudryavtsev
> > > > > > Bitworks Software, Ltd.
> > > > > > Cell: +7-923-414-1515
> > > > > > WWW: http://bitworks.software/ <http://bw-sw.com/>
> > > > > >
> > > > >
> > > >
> > > >
> > > >
> > > > --
> > > > Rafael Weingärtner
> > > >
> > >
> >
> >
> >
> > --
> > Rafael Weingärtner
> >
>



-- 
Rafael Weingärtner

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