how to identify queries using BLCed tables with the intention of throttling them in TASM.

Database
Enthusiast

how to identify queries using BLCed tables with the intention of throttling them in TASM.

Hi Team,

 

can you please help me the following.

 

  1. how to identify queries using BLCed tables with the intention of throttling them in TASM.
  2. how to identify which should not have BLC tables in DB
  3. how to remove BLC.

Thanks,

Shakthi.

1 REPLY
Teradata Employee

Re: how to identify queries using BLCed tables with the intention of throttling them in TASM.

  1. Note that within a table, some data blocks / logical cylinders may have BLC while others do not. Even if you defined all your tables with BLOCKCOMPRESSION ALWAYS / NEVER, that information is not available in TASM. You'd have to adopt some naming convention (e.g. prefix / suffix indicating BLC) that could be used in a TASM rule.
  2. It depends. For example, BLC tends to be a better choice for infrequently accessed data, and a poorer choice for frequently updated data. SoTemperature-Based BLC, especially when combined with partitioning, can be very useful (and one of the main reasons why you might have tables with a mix of compressed & uncompressed data blocks). But based on your platform characteristics (available CPU capacity, I/O bandwidth, storage capacity), you may sometimes be better off with BLC on nearly everything or on nothing at all.
  3. For an existing table, use the ferret utility. Or create a new table and copy the data (setting table attributes and/or query band appropriately to prevent compression).