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From kishore g <g.kish...@gmail.com>
Subject Re: Excessive ZooKeeper load
Date Wed, 04 Feb 2015 23:08:24 GMT
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 <varun@pinterest.com> 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 <g.kishore@gmail.com> 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" <varun@pinterest.com> 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 <zzhang@linkedin.com> 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 [varun@pinterest.com]
>>>> *Sent:* Monday, February 02, 2015 4:41 PM
>>>> *To:* user@helix.apache.org
>>>> *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,terrapinzk
>>>> 002b: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.zk
>>>> client.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 <varun@pinterest.com>
>>>> 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 <varun@pinterest.com>
>>>>> 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
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>

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