Checktable reports error 2791 or 2778 on dbc.objectusage WrittenFeb 28, 2017


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Teradata Database

In dbc.objectusage Teradata logs how often objects are accessed by SQL statements and the information is used by optimizer for stats extrapolation (Object Use Count aka OUC).
Checktable may report 2791 or 2778 errors like​ shown below on table dbc.objectusage.
This is caused by a problem where a correct OUC which is logged in the primary data row does not match an incorrect OUC which is logged in the fallback data row.
Since the access count of the objects is correct in the primary data row there is no impact to the operation of the system, because the fallback data row would never be accessed on a system which is up and running.
Also Change Control activities (upgrades, migrations, reconfig, etc.) are not impacted by this problem.
Example 2791 error from checktable level two:
"DBC"."OBJECTUSAGE" checking at 12:11:16 17/02/13.
  Table id 0000H 0121H
    2791: Primary and fallback data row checksums do not match.
          Primary AMP 00132
          Fallback AMP 00024, Fallback subtable 2048 (800H)
          Row id 0000000000000000 C162H D786H 0000H 0002H
Example 2778 error from checktable level three:
Table:  "DBC"."OBJECTUSAGE" checking at 10:39:39 16/11/19.
  Table id 0000H 0121H, Database id 0000H 0001H, Fallback.
    2778: Primary and fallback data rows do not match.
          Primary AMP 00042
          Fallback AMP 00090, Fallback subtable 2048 (800H)
          Row id 0000000000000000 07E7H B63CH 0000H 0001H


The cause of the problem is being investigated in DR 184457.​

When checktable reports these errors on any system, they can be ignored because the incorrect object use count on the fallback rows does not cause any negative impact on the customer system.
Even if the errors would be cleaned up, they would just re-appear again without the fix of DR 184457.
Therefore GSO DBS will not clean up these checktable errors on dbc.objectusage on a system without the fix for DR 184457.
Once the fix for DR 184457 ​is available and installed on a system, an incident can be opened to request GSO DBS to cleanup these errors.

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