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Oracle smart scan tips

Oracle Database Tips by Donald BurlesonMay 17, 2015

 

Question:  I hear of a new SQL execution plan scalled a smart scan that is available in Exadata.  How is a smart scan different from a regular table scan?

 

Answer:  According to Oracle a smart scan is "smart" because the scan only returns the requested rows for the SQL query.

 

Instead of reading-in an entire block, the smart scan has foreknowledge of the data requirements of the SQL and only retrieves those rows that are requested by the SQL.

To achieve this, Oracle now has an "intelligent database" (iDB) method for calling data in logical "storage cells" which map to disk at a lower level.

 

Oracle smart scans are not available for all types of full scan operations but the following query can list those SQL scans that can be made into intelligent smart scans:

 

select
   name
from
   v$sqlfn_metadata;

 

 In a sense, a "smart scan" is analogous to partition pruning  because Oracle knows only those areas that contain data that is needed for the query, bypassing those disk blocks that do not contain rows that are required by the SQL scan operation.

 

Oracle offers this query to show the savings of a smart scan, and also lists the "storage index" savings":

 

col stat_value format 9,999.9999

select
    decode(name,
    'cell physical IO bytes saved by storage index',
    'SI Savings',
    'cell physical IO interconnect bytes returned by smart scan',
    'Smart Scan'
    ) as stat_name,
    value/1024/1024 as stat_value
from
     v$mystat   s,
     v$statname n

where
    s.statistic# = n.statistic#
and
    n.name in (
    'cell physical IO bytes saved by storage index',
    'cell physical IO interconnect bytes returned by smart scan'
    )
/;

 

 
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