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From Marc-Aurèle Brothier <ma...@exoscale.ch>
Subject Re: [Discuss] Management cluster / Zookeeper holding locks
Date Mon, 18 Dec 2017 13:16:36 GMT
Sorry about the confusion. It's not going to replace the DB transactions in
the DAO way. Today we can say that there are 2 types of locks in CS, either
a pure transaction one, with the select for update which locks a row for
any operation by other threads, or a more programmatic one with the op_lock
table holding entries for pure locking mechanism used by the Merovigian
class. Zookeeper could be used to replace the latter, and wouldn't be a
good candidate for the other one.

To give more precise example of the replacement, it could be use to replace
the lock on VM operations, when only one opertion at a time must be
performed on a VM. It should not be used to replace locks in DAOs which
lock a VO entry to update some of its field.

Rafael,does that clarifies you thoughts and concerns about transactions,
connections ?

On Mon, Dec 18, 2017 at 1:10 PM, Rafael Weingärtner <
rafaelweingartner@gmail.com> wrote:

> 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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