IO Skew

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IO Skew

I m getting High IO skew on the system upon running a particular select query. It is making the system critical. What can be the remedy for this ? Stats are defined on the columns .

 

Can anyone please guide on the same ?

 

Maximum CURRENTPERMSKEW of the tables that are used are maximum 23 to 34.

1 REPLY
Teradata Employee

Re: IO Skew

High I/O Skew is typically due to an inefficient join. Be sure you have stats on the join and filter columns for both tables. You may need to look at step-level DBQL and/or Viewpoint Query Monitor to determine the step(s) with the issue and analyze the explain to see what the step(s) are doing.

 

The smaller the table, the less CurrentPermSkew is meaningful. I would ignore CurrentPermSkew unless MAX(CurrentPerm) for the table in DBC.TableSizeV is over 100MB or so.