15.10 - MERGEBLOCKRATIO - Teradata Database

Teradata Database SQL Data Definition Language Syntax and Examples

prodname
Teradata Database
vrm_release
15.10
created_date
December 2015
category
Programming Reference
featnum
B035-1144-151K

The merge block ratio to be used for this table when Teradata Database combines smaller data blocks into a single larger data block.

You can only specify a numeric merge block ratio for permanent base tables and permanent journal tables. You cannot specify a numeric merge block ratio for global temporary or volatile tables. You can, however, specify either the DEFAULT MERGEBLOCKRATIO or the NO MERGEBLOCKRATIO options for global temporary and volatile tables.

If you do not specify this option, Teradata Database uses the value that is specified for the MergeBlockRatio parameter in the DBS Control record at the time a data block merge operation on the table begins.

This value of the merge block ratio for a table does not affect the resulting block size when only a single block is modified. Setting the merge block ratio to too high a value can cause the resulting merged block to require being split during subsequent modifications.

The following list explains what the various options mean.

Whether Teradata Database uses the merge block ratio you specify depends on the setting for the DBS Control parameter DisableMergeBlocks. For details, see Utilities, B035-1102.

  • If DisableMergeBlocks is set FALSE, then the value you specify for MERGEBLOCKRATIO overrides the system-wide default setting for the DBS Control parameter MergeBlockRatio.
  • If DisableMergeBlocks is set TRUE, then Teradata Database ignores all table-level settings for the merge block ratio and does not merge data blocks for any table in the system.
DEFAULT
DEFAULT MERGEBLOCK RATIO, which is the default, means that Teradata Database uses the value for MergeBlockRatio that is defined by the DBS Control record at the time a data block merge operation on this table begins.
MERGEBLOCKRATIO = integer
Teradata Database uses the value specified by integer as the merge block ratio when a data block merge operation occurs on this table.
The valid range for integer is from 1 to 100, inclusive. The default value is 60.
PERCENT
Optional keyword to indicate that the value is a percentage.
NO MERGEBLOCKRATIO
NO MERGEBLOCKRATIO means that Teradata Database does not merge small data blocks for this table.