MERGEBLOCKRATIO

Database
Enthusiast

MERGEBLOCKRATIO

What is DEFAULT MERGEBLOCKRATIO in the table creation statement in TD 13 env?

Any explaination would help..!!

Thanks,

Biswajit

3 REPLIES
Enthusiast

Re: MERGEBLOCKRATIO

Please somebody help need know what is the importance of this feature.

Teradata Employee

Re: MERGEBLOCKRATIO

I found this in Teradata Database 13.10 Release Summary (B035-1098-109A) Page 18:

Allow Merging Data Blocks During Full File Operations

Description

This features enables the Teradata file system to dynamically merge up to eight small data

blocks into a single, large data block per full-table modification scan. The feature:

• Adds a MERGEBLOCKRATIO option to the CREATE TABLE and ALTER TABLE

statements. The new option defines a limit on the size of the resulting block when multiple

existing blocks are being merged.

• Affects Filer: The TABLE /L command displays the current table level attribute for

MergeBlockRatio stored in the table header.

• Adds two tunable fields to the DBSControl utility:

• MERGEBLOCKRATIO defines a limit on the size of the resulting block when multiple

existing blocks are merged. It is applied to all existing databases in all tables across the

system where no specific table-level attribute exists.

• DISABLEMERGEBLOCKS disables all database merges across the system, causing all

modification operations on a table to ignore any MERGEBLOCKRATIO that would

otherwise apply to the table.

Benefits

Having fewer, larger blocks reduces the I/O operations required to read from disk and modify

a large set of rows.

Considerations

The feature only affects the performance of workloads that modify data. Read-only workloads

and insert operations into new subtables are not affected.

Re: MERGEBLOCKRATIO

Check this link , it gives a detailed explanation for MERGEBLOCKRATIO :

http://www.info.teradata.com/HTMLPubs/DB_TTU_14_00/index.html#page/SQL_Reference/B035_1184_111A/Crea...