[jira] [Commented] (CASSANDRA-10792) Make warning level for count of partitions in unlogged BatchStatement configurable.

["Pawel Matras (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-10792?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15035464#comment-15035464 ] 

Pawel Matras commented on CASSANDRA-10792:
------------------------------------------

Sorry for creating confusion. Perhaps this comes from too long explanation or perhaps because I would like to give my vote for unlogged batches as they do perform better in some deployment scenarios (as I tried to explain above). Actually, I am a little bit afraid that they are on their way out of Cassandra as you recommend against them and warn users that they should do something else instead.

{quote}
It is my understanding that while we recommend against it, submitting batches for multiple partitions is currently possible. Is this not the case?
{quote}
Yes, it is possible. Creating of unlogged batches for multiple partitions works. Unfortunately in newer versions of Cassandra they produce lots of warnings in the server logs and it is quite hard to turn these warnings off. So my  improvement proposal suggests to introduce configuration parameter in cassandra.yaml e.g.
{noformat}
unlogged_batch_partitions_warn_threshold: 1
{noformat}
similar to existing {{batch_size_warn_threshold_in_kb}}. This new parameter will then be used in BatchStatement.verifyBatchType instead of todays hardcoded 1.

{quote}
What is the CQL syntax of the statement you are trying, and the schema of the table you are using?
{quote}
I am using DataStax java driver. Batch statement itself is created programmatically {{new BatchStatement( BatchStatement.Type.UNLOGGED )}}. Then  inserts are added to it by binding PreparedStatement created from CQL. Batch is executed asynchronously. Table is similar to (sorry, I am not allowed to provide details):
{noformat}
create table MY_TABLE (
   C1 varchar,
   C2 varchar,
   C3 varchar,
   C4 blob,
   primary key( (C1, C2), C3 )
);
{noformat}

In hope of clarification, best regards

Paweł

> Make warning level for count of partitions in unlogged BatchStatement configurable.
> -----------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-10792
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-10792
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Coordination
>         Environment: CentOS,  JDK 1.7, cluster of servers with 32 CPU each.
>            Reporter: Pawel Matras
>            Priority: Minor
>             Fix For: 3.2
>
>
> Currently mutations for only one partition are allowed in BatchStatement. This amount is hard coded and not configurable as e.g. batch size.
> General suggestion looks to be to consider multi partition unlogged batch statements as distributed anti pattern. As cure async inserts are proposed. Proposal might be OK if one consider only cassandra side of the system.
> If a complete system have to share the same hardware things does not look so obvious any more. When cassandra shares the same hardware with other also clustered components lots of small async inserts become another well known distributed anti pattern. 
> In our case changing from unlogged batches to async inserts destabilize the system as async inserts require amounts of interrupts per second and context switches per second beyond what hardware can handle. With replica aware unlogged batches these parameters are at 40% of hardware limits and the system as a whole runs stable without visible hotspots (cassandra metrics looks almost the same on all nodes).
> Unfortunately latest versions (we switched from 2.0.6 to 2.2.1) of cassandra log lots of warnings of type "Unlogged batch covering NN partitions detected against table XXX...". I found two workarounds to avoid this warning. The one is to use logged batches. But they generate 20% more interrupts and context switches and 400% more network load. The other way is more a hack and uses filtering features of logging framework and suppresses the warning just before it get logged.
> So my suggestion is to allow users of cassandra to decide by configuration if they consider unlogged batches antipattern or not. This is partially done with the size of the batch, where size is configurable and not hardcoded to 5 kB.
> It would be fine to stay consistent on this and let the user configure mutations for how many partitions to allow.
> Of course there are several other solutions possible here, probably more costly. E.g warning could be produced only if batch is not token/replica aware.



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