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From Patrick Hunt <ph...@apache.org>
Subject Re: zookeeper on SSD
Date Thu, 04 Oct 2012 04:28:51 GMT
On Wed, Oct 3, 2012 at 9:12 PM, Jun Rao <junrao@gmail.com> wrote:
> Patrick,
>
> Thanks for the info. Does each ZK write wait for log being flushed to disk?
>

Yes (it's necessary for the guarantees we provide), although the
servers do batching of writes to improve throughput. This doc gives
some insight: http://zookeeper.apache.org/doc/r3.4.4/zookeeperOver.html#Performance

Patrick


> On Wed, Oct 3, 2012 at 6:13 PM, Patrick Hunt <phunt@apache.org> wrote:
>
>> My experience with SSDs and ZK has been discouraging. SSDs have some
>> really terrible corner cases for latency. I've seen them take 40+
>> seconds (that's not a mistake - seconds) for fsync to complete. When
>> this happened (every few hours) all of the sessions would timeout.
>>
>> See this article:
>> http://storagemojo.com/2012/06/07/the-ssd-write-cliff-in-real-life/
>>
>> Patrick
>>
>> On Wed, Oct 3, 2012 at 9:59 AM, Jun Rao <junrao@gmail.com> wrote:
>> > Hi,
>> >
>> > Will storing the ZK commit log on SSD improve ZK write latency? Does a ZK
>> > write wait until data is flushed to disk?
>> >
>> > Thanks,
>> >
>> > Jun
>>

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