17.20 - Teradata Virtual Storage (VS): Migration Columns - Analytics Database - Teradata Database

Teradata Vantage™ - Resource Usage Macros and Tables - 17.20

Analytics Database
Teradata Database
Release Number
June 2022
English (United States)
Last Update
The ResUsageSvdsk table migration columns are populated only in Teradata VS. For more information, see Teradata Vantage™ - Teradata® Virtual Storage, B035-1179.

The migration columns identify the number of cylinders that migrated to a different location on a device as well as the time, in centiseconds, of all migration I/Os used, incurred, or saved during the log period.

Each allocation is for a cylinder size worth of data, also known internally in the allocator as an extent. Therefore, the column names begin with Ext for extent.
Column Name Mode Description Data Type
ExtMigrateFaster count Number of cylinders migrated to faster locations (that is, migrations whose gross benefits are positive) for the associated AMP.

The following formula calculates a Slower Migration value, which is the number of cylinders migrated to slower locations:

SlowerMigration = ExtMigrateTotal - ExtMigrateFaster

Cylinders are migrated to slower locations to make room for hotter cylinders to replace them.

ExtMigrateIOTimeCost count Estimates the total cost, in centiseconds, incurred by migration I/Os completing during the log period, where cost is the extra time waited by all non-migration I/Os as a result of the migration I/O. FLOAT
ExtMigrateIOTimeBenefit count Estimates the total I/O time savings achieved by migrations completing in the log period. The I/O time savings include the improvement in response time caused by the new data arrangement up to the time horizon.

This value does not include the cost of the migration I/Os and is a gross benefit, not a net benefit.

ExtMigrateIOTimeImprove count Estimates the percent improvement in average I/O response time due to migrations completing in the log interval.

For example, if, right before a particular log interval, the averageI/O response time was 10 milliseconds (ms), then the migration logs an ExtMigrateIOTimeImprove value of 10% in this interval. The average I/O response time after the log interval should be (100%-10%)*10ms = 9ms. Migration then logs an ExtMigrateIOTimeImprove of 1% in the next interval. The average I/O response time in the new log interval is (100%-1%)*9ms = 8.91ms.

ExtMigrateIOTimeImprove is only an estimate. Its permanent improvement remains in effect as long as the workload does not change and newer migrations do not significantly alter the data arrangement.

When the workload changes or new migrations affect data arrangement, response time changes in a nonquantifiable way.

You can use this field to predict the actual system performance for short periods of time and to understand why the migration algorithm is doing what it is doing.

ExtMigrateReadRespTot count Migration read I/O response time. FLOAT
ExtMigrateWriteRespTot count Migration write I/O response time. FLOAT
ExtMigrateTotal count Total number of cylinders migrated to a different physical location. For more information, see the ExtMigrateFaster column. FLOAT