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From Michael Segel <mse...@segel.com>
Subject Re: Latency in asynchronous mode
Date Thu, 30 Oct 2014 09:56:46 GMT
Sorry for the delay, work and travel... 

The numbers you posted:

So, when I run the stat command I get high latency like:
Latency min/avg/max: 7/339/392
Latency min/avg/max: 1/371/627
Latency min/avg/max: 1/371/627
Latency min/avg/max: 1/364/674
I guess such high latency correspond to fsync (batch requests). But I wish
if someone could help me and explain this behaviour. 

However, testing Zookeeper using Synchronous mode, it gives me reasonable
result like:
Latency min/avg/max: 6/24/55
Latency min/avg/max: 7/22/61
Latency min/avg/max: 7/30/65



Looking at the following:
Latency min/avg/max: 7/339/392
Latency min/avg/max: 6/24/55

Lets focus on the max,

392 vs 55. 

What does the 392 represent? 

The interesting thing is the min values of the latency numbers of the async. 1ms? 
But that's a different issue. 

So lets start there. 


-Mike

On Oct 25, 2014, at 6:44 PM, Ibrahim <i.s.el-sanosi@newcastle.ac.uk> wrote:

> Michael,
> 
> Ok,
> In part, the question is what are you actually seeing when you look at the numbers. Which
numbers do you mean?
> 
> Thank you
> 
> From: Michael Segel [via zookeeper-user] [mailto:ml-node+s578899n7580471h25@n2.nabble.com]
> Sent: Sunday, October 26, 2014 12:40 ص
> To: Ibrahim El-sanosi (PGR)
> Subject: Re: Latency in asynchronous mode
> 
> Hi,
> 
> I went back to the first email in this thread.
> 
> Which is why I asked if you understood the difference between synchronous and asynchronous
communication.
> You may understand it, but at the sometime not understand it.
> 
> In part, the question is what are you actually seeing when you look at the numbers.
> 
> 
> On Oct 25, 2014, at 8:16 PM, Ibrahim El-sanosi (PGR) <[hidden email]</user/SendEmail.jtp?type=node&node=7580471&i=0>>
wrote:
> 
>> Hi Michael,
>> 
>> Thank you for  your response.
>> 
>> No, I do understand the different between synchronous and asynchronous communication.
The question you are looking at is not my primary question, can you please check the main
question that I post. Again, the question you have answered is my replay to one of the user.
Also it is useful to follow the people replay to my question in order to become more familiar.
>> 
>> Thank you
>> 
>> Ibrahim
>> 
>> -----Original Message-----
>> From: Michael Segel [mailto:[hidden email]</user/SendEmail.jtp?type=node&node=7580471&i=1>]
>> Sent: Saturday, October 25, 2014 08:06 م
>> To: [hidden email]</user/SendEmail.jtp?type=node&node=7580471&i=2>
>> Subject: Re: Latency in asynchronous mode
>> 
>> Hi,
>> 
>> I am afraid I don’t understand your question.
>> 
>> Do you not understand the difference between synchronous and asynchronous communication?
>> 
>> Look: Synchronous… I’m not going to do anything until I hear from you or I time
out and resend my request.
>> Think of having a phone conversation. You say something and then wait for a response.
>> 
>> Asynchronous… I’m going to send a bit of information and then go on and do something
else and not wait for a response.
>> Think of writing a post-it note and leaving on the fridge for your wife to find.
Or leaving a voice mail message that you’re heading out to the pub for a quick drink and
you will be late to dinner. ;-)
>> 
>> Ok… I realize I’m stating the obvious… but that really should explain what
you are seeing.  The message is sent and then ZK goes on doing something else… and the response
is somewhere in the queue to be processed at a later time.  What’s wrong with that?
>> 
>> Your own results show that the more activity ZK is doing, the longer the delay in
receiving the ACK from the response.
>> 
>> -Mike
>> 
>> On Oct 23, 2014, at 7:21 PM, Ibrahim El-sanosi (PGR) <[hidden email]</user/SendEmail.jtp?type=node&node=7580471&i=3>>
wrote:
>> 
>>> Hi Rakesh,
>>> 
>>> First of all, the zookeeper ensemble consists of five Zookeeper servers. Also
I have another 10 clients machines used to send write requests to Zookeeper. The benchmark
code creates 5 threads (equal to number of Zookeeper server) , each thread associates with
one Zookeeper server. So, in this case, each zookeeper server will receive a set of write
requests. The benchmark code runs for 30 seconds.
>>> 
>>> Async tests:
>>> 
>>> * Number of clients
>>> In fact, I have different test, each test has different number of clients. For
example, the bellow shows the latency corresponds to different number of clients:
>>> Five clients: Latency min/avg/max: 235/366/515 Ten clients:  Latency
>>> min/avg/max: 252/368/505
>>> 
>>> * Number of threads
>>> As explained above, each client creates 5 threads and each thread connects to
one Zookeeper server. For instance, test using 5 clients’ machines, each Zookeeper server
receives five threads.
>>> 
>>> * data size storing in each znode
>>> The data size store in znode is 100 bytes
>>> 
>>> Also, it would be good to monitor :
>>> 
>>> 1) JVM stats(one way is through JMX) like heap, gc activities. This is to see
if latency spike corresponds to gc activity or not.
>>> 
>>> If you mean by JVM stats the four word stat command, then  the latency result
showed above is generated using this command. If you mean something else then I have to read
about and tell you late on.
>>> 
>>> 2) Since you are doubting fsync, I think $ iostat would be helpful to see disk
statistics. For example, $ iostat -d -x 2 10 and collects the disk latency.
>>> 
>>> Yes, the batch size that I use in SyncrequestProcessor class is 1000 requests.
I think this is preferable size. Also, I will try to use iostat.
>>> 
>>> 3) CPU usage through top or sar unix commands. I didn't use sar , but I could
see it gives more details like percent of CPU running idle with a process waiting for block
I/O etc.
>>> 
>>> Yes, I will use the top command to gathering the resource utilization. However,
I don’t think top or sar will answer my question. Because I am thinking there is different
between Asynchroned and Synchronized mode for measuring the latency.
>>> 
>>> Thank you for your attention
>>> 
>>> I look forward to hearing from you
>>> 
>>> 
>>> Ibrahim
>>> 
>>> -----Original Message-----
>>> From: Rakesh Radhakrishnan [mailto:[hidden email]</user/SendEmail.jtp?type=node&node=7580471&i=4>]
>>> Sent: Thursday, October 23, 2014 03:58 م
>>> To: [hidden email]</user/SendEmail.jtp?type=node&node=7580471&i=5>
>>> Subject: Re: Latency in asynchronous mode
>>> 
>>> Hi Ibrahim,
>>> 
>>> In async tests, could you give the details like:
>>> 
>>> * number of clients
>>> * number of threads
>>> * data size storing in each znode
>>> 
>>> Also, it would be good to monitor :
>>> 
>>> 1) JVM stats(one way is through JMX) like heap, gc activities. This is to see
if latency spike corresponds to gc activity or not.
>>> 
>>> 2) Since you are doubting fsync, I think $ iostat would be helpful to see disk
statistics. For example, $ iostat -d -x 2 10 and collects the disk latency.
>>> 
>>> 3) CPU usage through top or sar unix commands. I didn't use sar , but I could
see it gives more details like percent of CPU running idle with a process waiting for block
I/O etc.
>>> 
>>> 
>>> -Rakesh
>>> 
>>> 
>>> On Thu, Oct 23, 2014 at 6:44 PM, Alexander Shraer <[hidden email]</user/SendEmail.jtp?type=node&node=7580471&i=6>>
wrote:
>>> 
>>>> Maybe due to queueing at the leader in asynchronous mode - if in your
>>>> experiment you have one client in sync mode the leader has just one
>>>> op in the queue at a time On Oct 23, 2014 1:57 PM, "Ibrahim"
>>>> <[hidden email]</user/SendEmail.jtp?type=node&node=7580471&i=7>>
wrote:
>>>> 
>>>>> Hi folks,
>>>>> 
>>>>> I am testing ZooKeeper latency in Asynchronous mode. I am sending
>>>>> update
>>>>> (write) requests to Zookeeper cluster that consists of 5 physical
>>>>> Zookeeper.
>>>>> 
>>>>> So, when I run the stat command I get high latency like:
>>>>> Latency min/avg/max: 7/339/392
>>>>> Latency min/avg/max: 1/371/627
>>>>> Latency min/avg/max: 1/371/627
>>>>> Latency min/avg/max: 1/364/674
>>>>> I guess such high latency correspond to fsync (batch requests). But
>>>>> I
>>>> wish
>>>>> if someone could help me and explain this behaviour.
>>>>> 
>>>>> However, testing Zookeeper using Synchronous mode, it gives me
>>>>> reasonable result like:
>>>>> Latency min/avg/max: 6/24/55
>>>>> Latency min/avg/max: 7/22/61
>>>>> Latency min/avg/max: 7/30/65
>>>>> 
>>>>> Note that the latency measures in milliseconds.
>>>>> 
>>>>> I look forward to hearing from you.
>>>>> 
>>>>> Ibrahim
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> --
>>>>> View this message in context:
>>>>> 
>>>> http://zookeeper-user.578899.n2.nabble.com/Latency-in-asynchronous-mo
>>>> d
>>>> e-tp7580446.html
>>>>> Sent from the zookeeper-user mailing list archive at Nabble.com.
>>>>> 
>>>> 
>> 
> 
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