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From Bo Finnerup Madsen <bo.gunder...@gmail.com>
Subject Re: When are hints written?
Date Thu, 21 Apr 2016 06:05:59 GMT
Hi Jens,

Thank you for the tip!
ALL would definitely cure our hints issue, but as you note, it is not
optimal as we are unable to take down nodes without clients failing.

I am most probably overlooking something in the documentation, but I cannot
see any description of when hints are written other than when a node is
marked as being down. And since none of our nodes have been marked as being
down (at least according to the logs), I suspect that there is some timeout
that governs when hints are written?

Regarding your other post: Yes, 3.0.3 is pretty new. But we are new to this
cassandra game, and our schema-fu is not strong enough for us to create a
schema without using materialized views :)

ons. 20. apr. 2016 kl. 17.09 skrev Jens Rantil <jens.rantil@tink.se>:

> Hi Bo,
>
> > In our case, I would like for the cluster to wait for the write to be
> persisted on the relevant nodes before returning an ok to the client. But
> I don't know which knobs to turn to accomplish this? or if it is even
> possible :)
>
> This is what write consistency option is for. Have a look at
> https://docs.datastax.com/en/cassandra/2.0/cassandra/dml/dml_config_consistency_c.html.
> Note, however that if you use ALL, your clients will fail (throw exception,
> depending on language) as soon as a single partition can't be written. This
> means you can't do online maintenance of a Cassandra node (such as
> upgrading it etc.) without experiencing write issues.
>
> Cheers,
> Jens
>
> On Wed, Apr 20, 2016 at 3:39 PM Bo Finnerup Madsen <bo.gundersen@gmail.com>
> wrote:
>
>> Hi,
>>
>> We have a small 5 node cluster of m4.xlarge clients that receives writes
>> from ~20 clients. The clients will write as fast as they can, and the whole
>> process is limited by the write performance of the cassandra cluster.
>> After we have tweaked our schema to avoid large partitions, the load is
>> going ok and we don't see any warnings or errors in the cassandra logs. But
>> we do see quite a lot of hint handoff activity. During the load, the
>> cassandra nodes are quite loaded, with linux reporting a load as high as 20.
>>
>> I have read the available documentation on how hints works, and to my
>> understanding hints should only be written if a node is down. But as far as
>> I can see, none of the nodes are marked as down during the load. So I
>> suspect I am missing something :)
>> We have configured the servers with write_request_timeout_in_ms: 120000
>> and the clients with a timeout of 130000, but still get hints stored.
>>
>> In our case, I would like for the cluster to wait for the write to be
>> persisted on the relevant nodes before returning an ok to the client. But I
>> don't know which knobs to turn to accomplish this? or if it is even
>> possible :)
>>
>> We are running cassandra 3.0.3, with 8Gb heap and a replication factor of
>> 3.
>>
>> Thank you in advance!
>>
>> Yours sincerely,
>>   Bo Madsen
>>
> --
>
> Jens Rantil
> Backend Developer @ Tink
>
> Tink AB, Wallingatan 5, 111 60 Stockholm, Sweden
> For urgent matters you can reach me at +46-708-84 18 32.
>

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