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From Hiroyuki Yamada <mogwa...@gmail.com>
Subject Re: How does the "batch" commit log sync works
Date Fri, 28 Oct 2016 03:48:19 GMT
Hello Satoshi and the community,

I am also using commitlog_sync for durability, but I have never
modified commitlog_sync_batch_window_in_ms parameter yet,
so I wondered if it is working or not.

As Satoshi said, I also changed commitlog_sync_batch_window_in_ms (to
10000) and restarted C* and
issued some INSERT command.
But, it actually returned immediately right after issuing.

So, it seems like the parameter is not working correctly.
Are we missing something ?

Thanks,
Hiro

On Thu, Oct 27, 2016 at 5:58 PM, Satoshi Hikida <sahikida@gmail.com> wrote:
> Hi, all.
>
> I have a question about "batch" commit log sync behavior with C* version
> 2.2.8.
>
> Here's what I have done:
>
> * set commitlog_sync to the "batch" mode as follows:
>
>> commitlog_sync: batch
>> commitlog_sync_batch_window_in_ms: 10000
>
> * ran a script which inserts the data to a table
> * prepared a disk dedicated to store the commit logs
>
> According to the DataStax document, I expected that fsync is done once in a
> batch window (one fsync per 10sec in this case) and writes issued within
> this batch window are blocked until fsync is completed.
>
> In my experiment, however, it seems that the write requests returned almost
> immediately (within 300~400 ms).
>
> Am I misunderstanding something? If so, can someone give me any advices as
> to the reason why C* behaves like this?
>
>
> I referred to this document:
> https://docs.datastax.com/en/cassandra/2.2/cassandra/configuration/configCassandra_yaml.html#configCassandra_yaml__PerformanceTuningProps
>
> Regards,
> Satoshi
>

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