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From Frederic MOREAU <frederic_mor...@ds-fr.com>
Subject performance issue : indexes not taken into account on unions
Date Wed, 26 Oct 2005 11:47:10 GMT
Hello,

The optimizer does not take my indexes into account when I do a select on 
a 'UNION ALL' type of view ; therefore, table scans are done and 
performances are bad.

Note : my indexes are taken into account if I try equivalent selects on 
tables (instead of views).

Please find below a sample illustrating the problem using the 
RUNTIMESTATISTICS calls.

Could anynone help me on this subject ?
Thank you.


My cloudscape version is the 10.0.2.1 one.
I also tried it on the 10.1.1.0 version (same result).

  c:\>java -classpath 
"%CLOUDSCAPE_INSTALL%\lib\derbyclient.jar;%CLOUDSCAPE_INSTALL%\lib\derbytools.jar" 
-Dij.driver=org.apache.derby.jdbc.ClientDriver 
-Dij.protocol=jdbc:derby://localhost:1527/ -Dij.user=APP -Dij.password=APP 
-Dij.maximumDisplayWidth=32768 org.apache.derby.tools.ij  ij> connect 
'testdb' ;

  ij> ;
  ij> create table test.table1(a integer, b integer, c integer);
  ij> create index test.table1idx on test.table1(b);
  ij> ;
  ij> create table test.table2(a integer, b integer, c integer);
  ij> create index test.table2idx on test.table2(b);
  ij> ;
  ij> create view test.view0 as select all a,b from test.table1 union all 
select a,b from test.table2;
  ij> ;
  ij> CALL SYSCS_UTIL.SYSCS_SET_RUNTIMESTATISTICS(1);
  ij> select a from test.table1 where b=25;
  ij> VALUES SYSCS_UTIL.SYSCS_GET_RUNTIMESTATISTICS();
        ...
        Index Scan ResultSet for TABLE1 using index TABLE1IDX at read 
committed isolation level using instantaneous share row locking chosen by 
the optimizer
        ...
  ij> select a from test.table2 where b=25;
  ij> VALUES SYSCS_UTIL.SYSCS_GET_RUNTIMESTATISTICS();
        ...
        Index Scan ResultSet for TABLE2 using index TABLE2IDX at read 
committed isolation level using instantaneous share row locking chosen by 
the optimizer
        ...
  ij> select a from test.view0 where b=25;
  ij> VALUES SYSCS_UTIL.SYSCS_GET_RUNTIMESTATISTICS();
        ...
        Table Scan ResultSet for TABLE1 at read committed isolation level 
using share row locking chosen by the optimizer
        ...
        Table Scan ResultSet for TABLE2 at read committed isolation level 
using share row locking chosen by the optimizer
        ...
  ij> ;
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