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From "Anuj (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-8938) Full Row Scan does not count towards Reads
Date Thu, 09 Apr 2015 14:34:12 GMT


Anuj commented on CASSANDRA-8938:

I think counting it as one read would make the ready latency in cfstats misleading as range
scan may return nunerous rows and is generally slower. What about having a separate Range
scan count and latency. Range scan count can be equal to rows read in scan.   I think if a
range scan reads several rows from a sstable it should impact hotness propotionately. Cassandra
should not worry about the type of workload as data is being read and compaction will be useful
whether its analytics or oltp.

> Full Row Scan does not count towards Reads
> ------------------------------------------
>                 Key: CASSANDRA-8938
>                 URL:
>             Project: Cassandra
>          Issue Type: Bug
>          Components: API, Core, Tools
>         Environment: Unix, Cassandra 2.0.3
>            Reporter: Amit Singh Chowdhery
>            Assignee: Marcus Eriksson
>            Priority: Minor
>              Labels: none
> When a CQL SELECT statement is executed with WHERE clause, Read Count is incremented
in cfstats of the column family. But, when a full row scan is done using SELECT statement
without WHERE clause, Read Count is not incremented. 
> Similarly, when using Size Tiered Compaction, if we do a full row scan using Hector RangeslicesQuery,
Read Count is not incremented in cfstats, Cassandra still considers all sstables as cold and
does not trigger compaction for them. If we fire MultigetSliceQuery, Read Count is incremented
and sstables becomes hot, triggering compaction of these sstables. 
> Expected Behavior:
> 1. Read Count must be incremented by number of rows read during a full row scan done
using CQL SELECT statement or Hector RangeslicesQuery.
> 2. Size Tiered compaction must consider all sstables as Hot after a full row scan.

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