The SESSIONS parameter specifies the number of Teradata Database sessions that are available for archive and recovery operations. This number does not include any additional sessions that might be required to control archive and recovery operations.
where:
|
Syntax Element |
Definition |
|
nnn |
Number of data sessions. The default is 4. |
In general, the amount of system resources (that is, memory and processing power) that are required to support the archive or recovery increases with the number of sessions. The impact on a particular system depends on the specific configuration.
Teradata ARC uses at least two (or three) control sessions to control archive and recovery operations. The LOGON statement always connects these sessions no matter what type of operation being performed. Teradata ARC connects additional data sessions based on the number indicated in the SESSIONS parameter. These sessions are required for the parallel processing that occurs in archive and restore or copy operations.
If additional data sessions are required, Teradata ARC connects them at one time. Teradata ARC calculates the number of parallel sessions it can use, with maximum available being the number of sessions indicated with this parameter. Any connected sessions that are not actually used in the operation result in wasted system resources.
Table 15 indicates the data session requirements for archive and restore operations.
|
Operation |
Data Session Requirements |
|
All-AMPs archive |
No more than one session per AMP |
|
Cluster or specific archive |
Calculates the nearest multiple of online AMPs for the operation and assigns tasks evenly among the involved AMPs For example, if four AMPs are archived with nine sessions specified, Teradata ARC actually uses eight sessions (two per AMP). The extra connected session wastes system resources since it is unused. |
|
Restore/copy |
Use all the sessions specified using the sessions parameter |
Note: If Teradata Active System Management (TASM) is running on the system where a Teradata ARC job is running, TASM may override the SESSIONS value that the user has requested based on system utilization. If this should happen, ARC displays a message similar to the following:
ARC HAS REQUESTED 14 SESSIONS, TASM HAS GRANTED IT 4 SESSIONS.