ODBC Server Installation and Management Manual

Installing the NonStop ODBC Server
HP NonStop ODBC Server Installation and Management Manual—429395-002
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Dynamic Configuration
If a new server had been started to service the connection at time T3, or if another
server currently running under a different username and profile had been selected, the
new profile would have been brought into effect immediately when User A connected.
Configuration Update Option
Another system attribute that controls when some configuration changes take effect is
the LAST_UPDATE_SYSTEM_CONFIG attribute, also stored in the system
configuration defaults table, ZNSSCFG. This value is a timestamp that indicates when
the administrator last made a global change to configuration data. This mechanism lets
running processes ignore partial configuration data changes without requiring the
administrator to specify update locks. This avoidance of locks allows logins to continue
unimpeded while updates are occurring.
When a component checks for a configuration change, it checks to see if the
timestamp value of LAST_UPDATE_SYSTEM_CONFIG is later than when the last
check was made. If so, the component reviews each configuration entity and modifies
its current run environment to reflect any changes. If the timestamp is unchanged, the
component can resume processing without further checks on configuration data, as it
is either unchanged or within a cycle of change not yet completed. This technique
ensures that a coordinated set of configuration changes can all take effect at the same
time.
One consideration exists for this mechanism. Newly started servers read all
configuration attributes, regardless of whether or not a coordinated multiple attribute
configuration is completed—as in the case where the administrator has not completed
updates to each of the configuration elements. This activity occurs regardless of the
value for LAST_UPDATE_SYSTEM_CONFIG.
Figure 2-2. Timing of Dynamic Configuration
T1
T2 T3
T4
Connect
User A
Change Profile
P1 to P2
Connect
User A
Connect
User A
Disconnect
Disconnect
User A
Profile P1
User A
Profile P2
Time
Activity
Polling
Interval
Process
Environment
VST024.vsd