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https://issues.apache.org/jira/browse/TRAFODION-1900?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Eric Owhadi closed TRAFODION-1900.
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> Optimize MDAM scans with small scanner
> --------------------------------------
>
> Key: TRAFODION-1900
> URL: https://issues.apache.org/jira/browse/TRAFODION-1900
> Project: Apache Trafodion
> Issue Type: Improvement
> Components: sql-exe
> Reporter: Eric Owhadi
> Assignee: Eric Owhadi
> Fix For: 2.0-incubating
>
>
> When doing MDAM scans, we are performing interlaced scan for PROBE and for
> real scan. The probes always return only 1 row, then we close the scanner
> immediately, therefore should use always small scanner. I will make it
> conditional on the existing CQD HBASE_SMALL_SCANNER (ether SYSTEM or ON). In
> addition, caching of blocks retrieved by probe should always we at least
> receiving one succesfull cache hit on the next MDAM scan, therefore forcing
> caching ON for MDAM prob is a good idea. Again, will make this forcing
> conditional on HBASE_SMALL_SCANNER SYSTEM or ON.
> Then for the real scan part of MDAM, I will use the following heuristic: If
> previous scan fitted in one hbase block, then it is likelly than next will
> also fit in one hbase block, therefore enable small scanner for next scan.
> Again all this only if CQD above is ON or SYSTEM.
> Results of using small scanner on MDAM when it make sense showed a 1.39X
> speed improvement...
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