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From "Philip Thompson (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (CASSANDRA-10792) Make warning level for count of partitions in unlogged BatchStatement configurable.
Date Wed, 02 Dec 2015 15:18:11 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-10792?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Philip Thompson updated CASSANDRA-10792:
----------------------------------------
    Component/s:     (was: Coordination)
                 CQL
                 Configuration

> 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: Configuration, CQL
>         Environment: CentOS,  JDK 1.7, cluster of servers with 32 CPU each.
>            Reporter: Pawel Matras
>            Priority: Minor
>             Fix For: 3.x
>
>
> 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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