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RDBPROD: Dynamic Optimizer Uses Wrong Background Index Resulting in Bad Performance (Doc ID 1480189.1)

Last updated on AUGUST 12, 2016

Applies to:

Oracle Rdb Server on OpenVMS - Version 7.1 to 7.2.5.4 [Release 7.1 to 7.2]
HP OpenVMS Itanium
HP OpenVMS Alpha

Symptoms

An index has been recreated. Prior to this, the performance was good and the optimizer strategy looked like:

Leaf#01 FFirst THIS_TABLE Card=98375344
 BgrNdx1 INDEX_111 [4:3] Bool Fan=8
 BgrNdx2 INDEX_222 [1:0] Bool Fan=7
 BgrNdx3 INDEX_333 [1:0] Bool Fan=7
 BgrNdx4 INDEX_444 [1:0] Bool Fan=13
 BgrNdx5 INDEX_555 [1:0] Bool Fan=13
~E#0008.01(1) Estim   Index/Estimate 1/2791 5/2465814 2/3219129 4/5452188 3/6438259
~E#0008.01(1) BgrNdx1 EofBuf   DBKeys=1024  Fetches=8+8  RecsOut=0
~E#0008.01(1) BgrNdx5 EofBuf   DBKeys=1024  Fetches=5+3  RecsOut=0
~E#0008.01(1) BgrNdx1 EofBuf   DBKeys=2048* Fetches=0+43  RecsOut=0
...

After recreating INDEX_555, the performance was very bad and the optimizer strategy was shown as:

Leaf#01 FFirst THIS_TABLE Card=97213411
 BgrNdx1 INDEX_111 [4:3] Bool Fan=8
 BgrNdx2 INDEX_222 [1:0] Bool Fan=7
 BgrNdx3 INDEX_333 [1:0] Bool Fan=7
 BgrNdx4 INDEX_444 [1:0] Bool Fan=13
 BgrNdx5 INDEX_555 [1:0] Bool Fan=13
~E#0008.01(1) Estim   Index/Estimate 1/2791 2/3219129 4/5452188 5/5452188 3/6438259
~E#0008.01(1) BgrNdx1 EofBuf   DBKeys=1024  Fetches=8+8  RecsOut=0
~E#0008.01(1) BgrNdx2 EofBuf   DBKeys=1024  Fetches=7+580010  RecsOut=0
~E#0008.01(1) BgrNdx1 EofBuf   DBKeys=2048* Fetches=0+44  RecsOut=0
...

 
Index INDEX_222 is now chosen as the second background index, which resulted in 7+580010 fetches instead of 5+3 fetches.

Changes

An index has been recreated.

Cause

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In this Document
Symptoms
Changes
Cause
Solution
References


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