- Legacy space accounting makes cumulative space allocations to the AMPs that equal the maximum space value at allocation time, and the space limit for each AMP is set to the per-AMP quota. Vantage monitors the AMP space usage, and violations of space limitations are treated as exceptions, even if total use at the global database level is less than the maximum.
- Global space accounting allows AMPs to temporarily utilize space beyond per-AMP maximum space values on an as-needed basis, provided the space utilization does not exceed the database maximum. Space allocations and de-allocations for AMPs happen dynamically as needed in the background as modifications are made to database and user tables. The amount by which AMPs can utilize extra space is determined by the SKEW option in CREATE DATABASE and CREATE USER statements, or by the system default settings defined by DBS Control fields DefaultPermSkewLimitPercent, DefaultSpoolSkewLimitPercent, and DefaultTempSkewLimitPercent.
|TRUE||Vantage uses legacy space accounting, and prevents creation of databases and users with non-zero SKEW values.
Additionally, DSA perm space errors during archive/restore operations cause the operations to abort.
|FALSE||Vantage uses global space accounting, and allows creation of databases and users with non-zero SKEW values.
Additionally, DSA perm space errors during archive/restore operations are ignored, allowing the operations to continue to run.
Changes Take Effect
After the DBS Control record has been written.
- Regardless of the field setting, databases and users created with a SKEW value of zero will use legacy space accounting.
- The legacy space accounting method does not have the overhead of dynamic need-based space allocations. It is best suited when the database is expected to have uniform data distribution across all the AMPs in the system, or the global limit is set high enough to allow for variability in data distribution due to skew in the data.
- The global space accounting method is best suited when the actual space usage is expected to be non-uniform across the AMPs.
|For more information on...||See...|
|the SKEW option for DDL, such as CREATE DATABASE and CREATE USER||Teradata Vantage™ - SQL Data Definition Language Syntax and Examples, B035-1144.|
|related DBS Control fields|