SESAM/SQL supports two administration commands are available for increasing the availability of the independent DBH, for importing a correction version of the DBH while DBH operation is in progress, and for dynamic reconfiguration of the DBH session:
RECONFIGURE-DBH-SESSION
RELOAD-DBH-SESSION
Both administration statements are executed without interrupting the DBH session. From the user viewpoint no DBH failure occurs.
The following DBH options can be changed in the ongoing DBH session with RECONFIGURE-DBH-SESSION:
DBH option COLUMNS
DBH option CURSOR-BUFFER, parameters BUFFER-SIZE and FRAME-SIZE
DBH option SPACES
DBH option SQL-SUPPORT, parameters CURSORS and PLANS
DBH option SYSTEM-DATA-BUFFER
DBH option TRANSACTION-SECURITY, parameter MAX-ISOLATION-LEVEL
DBH option USER-DATA-BUFFER
The DBH modules are reloaded with RELOAD-DBH-SESSION. In this case the following DBH options can be changed in the ongoing DBH session:
DBH option DBH-TASKS
DBH option SYSTEM-THREADS, parameter WRITE-THREADS
DBH option THREADS
DBH option USERS
To reload the DBH modules SESAM/SQL must be installed with IMON. SESAM/SQL determines the current installation path and uses it to load the most up-to-date correction status of the DBH automatically. The new correction status of the DBH can have been installed in parallel to the version used to date, see section “Parallel use of multiple correction statuses”.
When a new correction status of the DBH is loaded, SESAM performance monitors which monitor this DBH must be restarted.
When the DBH session is dynamically reconfigured, the DBH’s memory is restructured or re-created. This also causes the counters which the SESMON performance monitor evaluates for statistical purposes to be reset to “0”.
Executing administration statements
To execute one of these statements, a transaction-free status of the DBH session is first required. Open transactions are aborted or reset by the DBH.
In the following cases the DBH cannot abort transactions. In these cases the administration statement is aborted with a corresponding message.
A transaction is in the processing phase Prepare To Commit (PTC)
A utility statement is being processed
A lock sequence has occurred
The start of DBH reconfiguration is reported in message SES6090 (independently of the DHB option MSG-OUTPUT) on the console or terminal and to SYSLST.
When an error occurs, if for example the DBH cannot be reconfigured because of a storage shortage, reconfiguration is aborted. If an external restart is initiated after reconfiguration has been aborted, the DBH is started with the DBH options used to date.
As with a start or restart, the operability of the DBH is displayed with the message SES0060 SESAM SYSTEM READY.