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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 14:44:13 GMT


Anuj commented on CASSANDRA-8938:

In our case we do some reporting using full table scans in off hours when resources are free.
We dont have an Analytics system like Spark. If sstables are not compacted it affects reporting
performance badly. So I think Cassandra should be unbiased. If a data is read actively we
will gain performance in bothh workloads. Compaction will have cost and will impact transactional
resources temporarily but further Analytics hits would be much faster and those hits will
put less load on cassandra resources if tables are compacted. 

> 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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