If a single instance of Historical Server is managing many concurrent recording sessions that have short sample intervals, the amount of time required to process and record the samples may interfere with the timely acquisition of new samples. If the timestamps in the recorded data files indicate that samples are not being collected at a reasonable approximation of the requested sample interval, you may choose to spread the load among two or more instances of Historical Server.
When multiple instances of Historical Server use the same home directory:
Each instance must be started by the same operating system account.
All instances that use the same home directory use the same control file.
The sessions recorded by one instance are visible to the other instances.
File locking mechanisms ensure that the control file is not corrupted by concurrent accesses.
When multiple instances of Historical Server use different home directories:
The Historical Server instances can be started by different user accounts.
The Historical Server instances use different control files.
The recording sessions of one server are not visible to the others. For example, the hs_list command, issued through isql, cannot access the recording sessions defined by another Historical Server using a different home directory.
When deciding whether multiple instances should use the same or different home directories, consider these factors:
Visibility of data – if users of the multiple instances need access to each other’s recording session definitions, use the same home directory. If sharing is undesirable, use different home directories. All input sessions to a playback session must be in the same home directory.
Visibility of status information – the hs_status command cannot distinguish between multiple instances of Historical Server using the same home directory. If this distinction is important to Historical Server administration, use different home directories.
Contention on the control file – if a large control file receives heavy access from multiple users, different home directories might mean better user response time. Actions such as creating recording sessions and listing information about recording sessions use the control file; recording sessions themselves, when they are running, do not block other users from the control file.
