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Message Posted: Wed, 03 Aug 2011 @ 20:17:35 GMT


     
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Subj:   MVC, VARCHAR, v13.10, error 9471
 
From:   Gregg, William

THANK YOU IN ADVANCE

Your help is appreciated. I will share any findings with the Forum.


QUESTIONS and OBSERVATIONS

Has anyone successfully compressed VARCHAR under 13.10? Under what circumstances? Changed any DBS settings?

More questions at the bottom of the note.


ENVIRONMENT

-- per DBC.dbcInfo, our shop is using release 13.10.01.02 and version 13.10.01.04 for this scenario.

-- using a proprietary tool to perform multi value compression (MVC) analysis.


THE EVENT

All seemed well when decimal, integer, char, and other v12 tolerant datatypes were compressed.

When we tried to compress VARCHAR our tool did its analysis and came back with a compression recommendation that looked reasonable. (Note: the max VARCHAR column size is 256, no testing of the 510 character limit for CHAR yet.)

When I tried to install the DDL (implementing the compression) , up popped a 9471.


DOCUMENTATION

Per the MESSAGES manual:

9471 Algorithmic Compression feature not yet enabled.

Explanation: The algorithmic compression feature will be enabled only when the Dbscontrol internal flag No13dotBackdown is set to TRUE.

Generated By: SYN/RES.

For Whom: End User.

Remedy: Enable No13dot0Backdown in Dbscontrol after understanding the limitations in so doing.

The error message suggests that AlgCompr needs to be in place to support VarChar compression. SURPRISE.

The 13.10 RELEASE SUMMARY (COMPRESSION ENHANCEMENTS, pp. 28-31) indicates that MVC works with/without Algorithmic or Block Level Compression (BLC). The Summary specifically states not to mix AlgCompr and BLC, but encourages using MVC with AlgCompr or BLC.


QUESTIONS and OBSERVATIONS

Are there other issues with VARCHAR compression and Teradata is struggling to send the correct message back to the user?

Does something need to be enabled underneath the sheets?

We would prefer to test the 13.10 MVC without having to commit to either AlgCompr or BLC to try VARCHAR compression.

Has anyone successfully compressed VARCHAR? Under what circumstances? Changed any DBS settings?

Again, your help is appreciated. I will share any findings with the Forum.


Rgrds,

Bill Gregg
Teradata DBA; GE



     
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