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 < rafaelweingart...@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 <ma...@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 < > > rafaelweingart...@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 < > ma...@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 < > > > > rafaelweingart...@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 < > > > ma...@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...@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 < > > > > > > rafaelweingart...@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...@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 < > > > > ma...@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 >
