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From Jeff Jirsa <>
Subject Re: Partition size
Date Fri, 09 Sep 2016 19:50:07 GMT

On 9/9/16, 8:47 AM, "Rakesh Kumar" <> wrote:

>> If your partition sizes are over 100MB iirc then you'll normally see
>> warnings in your system.log, this will outline the partition key, at least
>> in Cassandra 2.0 and 2.1 as I recall.
>Has it improved in C* 3.x. What is considered a good partition size in C* 3.x

In modern versions (2.1 and newer), the “real” risk of large partitions is that they generate
a lot of garbage on read – it’s not a 1:1 equivalence, but it’s linear, and a partition
that’s 10x as large generates 10x as much garbage.

You can tune around it (very large new gen, for example), but it’s best fixed at the data
model most of the time.

The long term fix will be Cassandra-9754, which is a work in progress. The short term fix
for 3.x was , which went into 3.6 and

In the notes on 11206, you’ll see that Robert Stupp tested up to an 8GB partition – while
nobody’s going to recommend you create a data model with 8gb partitions, I imagine you may
find partitions in that rough order of magnitude acceptable.

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