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https://issues.apache.org/jira/browse/CASSANDRA-12048?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Anuj Wadehra updated CASSANDRA-12048:
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Environment: Cassandra 2.0.x, 2.1.x, 2.2.x (was: Cassandra 2.2.x)
> Bucket_low property has no effect in STCS Algo
> ----------------------------------------------
>
> Key: CASSANDRA-12048
> URL: https://issues.apache.org/jira/browse/CASSANDRA-12048
> Project: Cassandra
> Issue Type: Bug
> Components: Compaction
> Environment: Cassandra 2.0.x, 2.1.x, 2.2.x
> Reporter: Anuj Wadehra
>
> It seems that the STCS algorithm is not impacted by setting the Bucket_low
> Compaction property. Also,I see some optimization in STCS algo.
> Problems:
> 1. getBuckets() method of SizeTieredCompactionStrategy sorts sstables by size
> in ascending order and then iterates over them one by one to associate them
> to an existing/new bucket. When, iterating sstables in ascending order of
> size, I can't find ANY single scenario where the current sstable in the outer
> loop iteration is below the oldAverageSize of any existing bucket. Current
> sstable being iterated will ALWAYS be greater than/equal to the
> oldAverageSize of ALL existing buckets as ALL previous sstables in existing
> buckets were smaller/equal in size to the sstable being iterated.
> So, there is NO scenario when size > (oldAverageSize * bucketLow) and size <
> oldAverageSize, so bucket_low property never comes into play no matter what
> value you set for it.
> 2. While iteraitng over sstables (sortedfiles) by size in ascending order,
> there is no point iterating over all existing buckets. We could just start
> from the LAST bucket where previous sstable was associated. oldAverageSize
> of ALL other buckets will NEVER allow the sstable being iterated.
> for (Entry<Long, List<T>> entry : buckets.entrySet())
> {...}
>
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