Process Scheduling: Cylinder Read Columns - Advanced SQL Engine - Teradata Database

This column records the number of attempts to use Cylinder Read independent of whether the request will be issued to FSG or not. A request can be denied due to insufficient data blocks or because there is insufficient space in the FSG cache. Requests can also be denied at both the user and kernel level. Each of these items is counted in other FileFcr resource usage columns.

This column can perform a number of calculations:

• Requests issued to FSG =

  FileFcrRequests - FileFcrDeniedUser

• Successful Cylinder Reads =

  FileFcrRequests - FileFcrDeniedUser - FileFcrDeniedKern

This column records the number of data blocks that were part of attempts to use Cylinder read that were denied by the FSG subsystem due to insufficient cache space; therefore, also incremented the FileFcrDeniedCache column.

This column records the number of data blocks that were part of attempts to use Cylinder Read that were denied by the FSG subsystem, and therefore, also incremented the FileFcrDeniedKern column.

This column records the number of data blocks that were part of attempts to use Cylinder Read that were denied by the File System.

This column records the number of data blocks that were part of attempts to use Cylinder read that were denied by the FSG subsystem due to the number of blocks being below the threshold, and therefore, also incremented the FileFcrDeniedThreshKern column.

This column records the number of data blocks that were part of attempts to use Cylinder Read that were denied by the File System due to the number of blocks being below the threshold, and therefore, also incremented the FileFcrDeniedThreshUser column.

This column records the total number of data blocks read in by successful Cylinder Read operations.

The average number of data blocks in a successful Cylinder read can be calculated as follows:

Average data blocks/ Cylinder Read = FileFcrBlocksRead / (FileFcrRequests - FileFcrDeniedUser - FileFcrDeniedKern)

This column records the number of Cylinder Read requests denied due to insufficient FSG cache space for a cylinders worth of data.

This column records the number of Cylinder Read requests issued to the FSG subsystem which, for any reason, have been denied. A request can be denied due to insufficient data blocks (for example, the FileFcrDeniedThreshKern column) or because there is insufficient space in the FSG cache (for example, the FileFcrDeniedCache column). The FSG subsystem can reject a request containing insufficient data blocks that the File System thought had enough blocks because the FSG subsystem reduces the count by the number of data blocks that are already resident in the cache.

This column records the number of Cylinder Read attempts denied by the File System. A request can be denied by the File System due to insufficient number of data blocks being requested (for example, the FileFcrDeniedThreshUser column). For information, see the FileFcrDeniedThreshUser column.

This column records the number of Cylinder Read requests denied due to the data block threshold criteria. There is a minimum threshold of data blocks for an individual Cylinder Read request. If the number of data blocks is below this threshold, the overhead of the Cylinder Read operation is considered too large and issuing individual data block reads is considered more efficient. Therefore, the Cylinder Read request is denied. FSG must reevaluate the threshold for a request that the File System considered valid since FSG eliminates any data blocks from the request list that are already resident in the cache. This could reduce the count that the File System thought was above the threshold to one that is now below.