Hi Varun, for the batching update. Helix controller is not updating external view on every update. Normally Helix controller will aggregate updates during a period of time. Say for 100 partitions, if they are updated roughly as the same time, then Helix controller will update external view only once. For routing table, what do you mean by ignoring delete events? RoutingTable will always be updated by ZK callbacks and sync up with the corresponding external views on ZK.
Thanks, Jason ________________________________ From: Varun Sharma [[email protected]] Sent: Thursday, February 05, 2015 9:17 PM To: [email protected] Subject: Re: Excessive ZooKeeper load One more question for the routing table provider - is it possible to distinguish b/w add/modify and delete - I essentially want to ignore the delete events - can that be found by looking at the list of ExternalView(s) being passed ? Thanks Varun On Thu, Feb 5, 2015 at 8:48 PM, Varun Sharma <[email protected]<mailto:[email protected]>> wrote: I see - one more thing - there was talk of a batching mode where Helix can batch updates - can it batch multiple updates to the external view and write once into zookeeper instead of writing for every update. For example, consider the case when lots of partitions are being onlined - if we could batch updates to the external view into batches of 100 ? Is that supported in Helix 0.6.4 Thanks ! Varun On Thu, Feb 5, 2015 at 5:23 PM, Zhen Zhang <[email protected]<mailto:[email protected]>> wrote: Yes. the listener will be notified on add/delete/modify. You can distinguish if you have a local cache and compare to get the delta. Currently the API doesn't expose this. ________________________________ From: Varun Sharma [[email protected]<mailto:[email protected]>] Sent: Thursday, February 05, 2015 1:53 PM To: [email protected]<mailto:[email protected]> Subject: Re: Excessive ZooKeeper load I assume that it also gets called when external views get modified ? How can i distinguish if there was an Add, a modify or a delete ? Thanks Varun On Thu, Feb 5, 2015 at 9:27 AM, Zhen Zhang <[email protected]<mailto:[email protected]>> wrote: Yes. It will get invoked when external views are added or deleted. ________________________________ From: Varun Sharma [[email protected]<mailto:[email protected]>] Sent: Thursday, February 05, 2015 1:27 AM To: [email protected]<mailto:[email protected]> Subject: Re: Excessive ZooKeeper load I had another question - does the RoutingTableProvider onExternalViewChange call get invoked when a resource gets deleted (and hence its external view znode) ? On Wed, Feb 4, 2015 at 10:54 PM, Zhen Zhang <[email protected]<mailto:[email protected]>> wrote: Yes. I think we did this in the incubating stage or even before. It's probably in a separate branch for some performance evaluation. ________________________________ From: kishore g [[email protected]<mailto:[email protected]>] Sent: Wednesday, February 04, 2015 9:54 PM To: [email protected]<mailto:[email protected]> Subject: Re: Excessive ZooKeeper load Jason, I remember having the ability to compress/decompress and before we added the support to bucketize, compression was used to support large number of partitions. However I dont see the code anywhere. Did we do this on a separate branch? thanks, Kishore G On Wed, Feb 4, 2015 at 3:30 PM, Zhen Zhang <[email protected]<mailto:[email protected]>> wrote: Hi Varun, we can certainly add compression and have a config for turning it on/off. We do have implemented compression in our own zkclient before. The issue for compression might be: 1) cpu consumption on controller will increase. 2) hard to debug Thanks, Jason ________________________________ From: kishore g [[email protected]<mailto:[email protected]>] Sent: Wednesday, February 04, 2015 3:08 PM To: [email protected]<mailto:[email protected]> Subject: Re: Excessive ZooKeeper load we do have the ability to compress the data. I am not sure if there is a easy way to turn on/off the compression. On Wed, Feb 4, 2015 at 2:49 PM, Varun Sharma <[email protected]<mailto:[email protected]>> wrote: I am wondering if its possible to gzip the external view znode - a simple gzip cut down the data size by 25X. Is it possible to plug in compression/decompression as zookeeper nodes are read ? Varun On Mon, Feb 2, 2015 at 8:53 PM, kishore g <[email protected]<mailto:[email protected]>> wrote: There are multiple options we can try here. what if we used cacheddataaccessor for this use case?.clients will only read if node has changed. This optimization can benefit all use cases. What about batching the watch triggers. Not sure which version of helix has this option. Another option is to use a poll based roundtable instead of watch based. This can coupled with cacheddataaccessor can be over efficient. Thanks, Kishore G On Feb 2, 2015 8:17 PM, "Varun Sharma" <[email protected]<mailto:[email protected]>> wrote: My total external view across all resources is roughly 3M in size and there are 100 clients downloading it twice for every node restart - thats 600M of data for every restart. So I guess that is causing this issue. We are thinking of doing some tricks to limit the # of clients to 1 from 100. I guess that should help significantly. Varun On Mon, Feb 2, 2015 at 7:37 PM, Zhen Zhang <[email protected]<mailto:[email protected]>> wrote: Hey Varun, I guess your external view is pretty large, since each external view callback takes ~3s. The RoutingTableProvider is callback based, so only when there is a change in the external view, RoutingTableProvider will read the entire external view from ZK. During the rolling upgrade, there are lots of live instance change, which may lead to a lot of changes in the external view. One possible way to mitigate the issue is to smooth the traffic by having some delays in between bouncing nodes. We can do a rough estimation on how many external view changes you might have during the upgrade, how many listeners you have, and how large is the external views. Once we have these numbers, we might know the ZK bandwidth requirement. ZK read bandwidth can be scaled by adding ZK observers. ZK watcher is one time only, so every time a listener receives a callback, it will re-register its watcher again to ZK. It's normally unreliable to depend on delta changes instead of reading the entire znode. There might be some corner cases where you would lose delta changes if you depend on that. For the ZK connection issue, do you have any log on the ZK server side regarding this connection? Thanks, Jason ________________________________ From: Varun Sharma [[email protected]<mailto:[email protected]>] Sent: Monday, February 02, 2015 4:41 PM To: [email protected]<mailto:[email protected]> Subject: Re: Excessive ZooKeeper load I believe there is a misbehaving client. Here is a stack trace - it probably lost connection and is now stampeding it: "ZkClient-EventThread-104-terrapinzk001a:2181,terrapinzk002b:2181,terrapinzk003e:2181" daemon prio=10 tid=0x00007f534144b800 nid=0x7db5 in Object.wait() [0x00007f52ca9c3000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) at java.lang.Object.wait(Object.java:503) at org.apache.zookeeper.ClientCnxn.submitRequest(ClientCnxn.java:1309) - locked <0x00000004fb0d8c38> (a org.apache.zookeeper.ClientCnxn$Packet) at org.apache.zookeeper.ZooKeeper.exists(ZooKeeper.java:1036) at org.apache.zookeeper.ZooKeeper.exists(ZooKeeper.java:1069) at org.I0Itec.zkclient.ZkConnection.exists(ZkConnection.java:95) at org.I0Itec.zkclient.ZkClient$11.call(ZkClient.java:823) at org.I0Itec.zkclient.ZkClient.retryUntilConnected(ZkClient.java:675) at org.I0Itec.zkclient.ZkClient.watchForData(ZkClient.java:820) at org.I0Itec.zkclient.ZkClient.subscribeDataChanges(ZkClient.java:136) at org.apache.helix.manager.zk.CallbackHandler.subscribeDataChange(CallbackHandler.java:241) at org.apache.helix.manager.zk.CallbackHandler.subscribeForChanges(CallbackHandler.java:287) at org.apache.helix.manager.zk.CallbackHandler.invoke(CallbackHandler.java:202) - locked <0x000000056b75a948> (a org.apache.helix.manager.zk.ZKHelixManager) at org.apache.helix.manager.zk.CallbackHandler.handleDataChange(CallbackHandler.java:338) at org.I0Itec.zkclient.ZkClient$6.run(ZkClient.java:547) at org.I0Itec.zkclient.ZkEventThread.run(ZkEventThread.java:71) On Mon, Feb 2, 2015 at 4:28 PM, Varun Sharma <[email protected]<mailto:[email protected]>> wrote: I am wondering what is causing the zk subscription to happen every 2-3 seconds - is this a new watch being established every 3 seconds ? Thanks Varun On Mon, Feb 2, 2015 at 4:23 PM, Varun Sharma <[email protected]<mailto:[email protected]>> wrote: Hi, We are serving a few different resources whose total # of partitions is ~ 30K. We just did a rolling restart fo the cluster and the clients which use the RoutingTableProvider are stuck in a bad state where they are constantly subscribing to changes in the external view of a cluster. Here is the helix log on the client after our rolling restart was finished - the client is constantly polling ZK. The zookeeper node is pushing 300mbps right now and most of the traffic is being pulled by clients. Is this a race condition - also is there an easy way to make the clients not poll so aggressively. We restarted one of the clients and we don't see these same messages anymore. Also is it possible to just propagate external view diffs instead of the whole big znode ? 15/02/03 00:21:18 INFO zk.CallbackHandler: 104 END:INVOKE /main_a/EXTERNALVIEW listener:org.apache.helix.spectator.RoutingTableProvider Took: 3340ms 15/02/03 00:21:18 INFO zk.CallbackHandler: 104 START:INVOKE /main_a/EXTERNALVIEW listener:org.apache.helix.spectator.RoutingTableProvider 15/02/03 00:21:18 INFO zk.CallbackHandler: pinacle2084 subscribes child-change. path: /main_a/EXTERNALVIEW, listener: org.apache.helix.spectator.RoutingTableProvider@76984879 15/02/03 00:21:22 INFO zk.CallbackHandler: 104 END:INVOKE /main_a/EXTERNALVIEW listener:org.apache.helix.spectator.RoutingTableProvider Took: 3371ms 15/02/03 00:21:22 INFO zk.CallbackHandler: 104 START:INVOKE /main_a/EXTERNALVIEW listener:org.apache.helix.spectator.RoutingTableProvider 15/02/03 00:21:22 INFO zk.CallbackHandler: pinacle2084 subscribes child-change. path: /main_a/EXTERNALVIEW, listener: org.apache.helix.spectator.RoutingTableProvider@76984879 15/02/03 00:21:25 INFO zk.CallbackHandler: 104 END:INVOKE /main_a/EXTERNALVIEW listener:org.apache.helix.spectator.RoutingTableProvider Took: 3281ms 15/02/03 00:21:25 INFO zk.CallbackHandler: 104 START:INVOKE /main_a/EXTERNALVIEW listener:org.apache.helix.spectator.RoutingTableProvider
