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https://issues.apache.org/jira/browse/CASSANDRA-4710?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13462360#comment-13462360
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Daniel Norberg commented on CASSANDRA-4710:
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The check against DatabaseDescriptor.getIndexInterval is to be able to exit the
loop in case the key looked for is not present in the index.
When doing token comparison the loop can be exited when an index entry whose
token is greater than the needle is encountered as the index is sorted on
token. I.e. the if (v < 0) return null. But when doing raw key comparison we
have to look through every entry in the section of the index that the sampled
index gave us to be able to know that a key was not present. Fortunately this
should be rare as key presence is checked using the bloom filter for EQ lookups
before reading the index.
> High key hashing overhead for index scans when using RandomPartitioner
> ----------------------------------------------------------------------
>
> Key: CASSANDRA-4710
> URL: https://issues.apache.org/jira/browse/CASSANDRA-4710
> Project: Cassandra
> Issue Type: Bug
> Reporter: Daniel Norberg
> Attachments:
> 0001-SSTableReader-compare-raw-key-when-scanning-index.patch
>
>
> For a workload where the dataset is completely in ram, the md5 hashing of the
> keys during index scans becomes a bottleneck for reads when using
> RandomPartitioner, according to profiling.
> Instead performing a raw key equals check in SSTableReader.getPosition() for
> EQ operations improves throughput by some 30% for my workload (moving the
> bottleneck elsewhere).
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