Is WaitIO and UII (unnecessary IO) are related?

Database
Teradata Employee

Is WaitIO and UII (unnecessary IO) are related?

Hello,

 

We have an appliance system. There is a single ETL query that runs early morning which has UII factor of 2.1.

Query uses complex and nested views and I observed that at execution step no 630 and (Merge Join, redistrubution parallel block of steps)

and step no 642 (Merge Join, redistrubution parallel block of steps) the WaitIO touches 80% in metric analysis portlet of viewpoint.waitIO.png

In both the execution steps the redistribution step completes in just 30-50 seconds.

As shown in above screen shot I observed the WaitIO spike of 80% at step 630 starting from 2:08 AM to 2:16AM i.e. 8 minutes.

For step 642 there is a spike starting from 2:19AM to 2:25AM i.e.6 minutes.

Normally UII factor >3 means there is more IO happening on the system. If here in this case if UII is 2 then is it performance degradation?

Does merge join is causing WaitIO of 80%?

 

 

 

 

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