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                              WORKLOG TASK
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TASK...........: Better choice between range and index_merge/intersection options
CREATION DATE..: Wed, 27 May 2009, 15:20
SUPERVISOR.....: Monty
IMPLEMENTOR....: Psergey
COPIES TO......: 
CATEGORY.......: Server-RawIdeaBin
TASK ID........: 26 (http://askmonty.org/worklog/?tid=26)
VERSION........: Server-9.x
STATUS.........: Un-Assigned
PRIORITY.......: 60
WORKED HOURS...: 0
ESTIMATE.......: 0 (hours remain)
ORIG. ESTIMATE.: 0

PROGRESS NOTES:



DESCRIPTION:

The optimizer does a cost-based choice between possible range and
index_merge/intersection scans.  There are some issues with it:

- index_merge/intersection gets chosen even when there is a single 
  multi-part index that covers all keys. Measurements show that this is 
  a poor choice.

- The picked index_merge/intersection can use a redundant set of indexes:
  it will be intersect(idx1, ..., idxN) where all columns in idxN are covered
  by other used indexes.

This WL is to fix these limitations.


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