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From "Phil Yang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-8938) Full Row Scan does not count towards Reads
Date Thu, 12 Mar 2015 08:52:39 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8938?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14358327#comment-14358327
] 

Phil Yang commented on CASSANDRA-8938:
--------------------------------------

The "readLatency" is a counter both counting "read count" and "read latency" for the query
with WHERE clause. I think the reason that nodetool only show the count of readLatency rather
than readLatency+rangeLatency is that usually it is not a good idea to select the whole table(because
it will read all sstables in all nodes) so it is not commonly used and usually be zero. 

Anyone other think the read count and read latency should add the counter of range read?

Why do you think all sstables must be available for next compaction after a range read? It
has few help for range read and compaction will increase the load of all nodes.

> Full Row Scan does not count towards Reads
> ------------------------------------------
>
>                 Key: CASSANDRA-8938
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8938
>             Project: Cassandra
>          Issue Type: Bug
>          Components: API, Core, Tools
>         Environment: Unix, Cassandra 2.0.3
>            Reporter: Amit Singh Chowdhery
>            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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