Tuning HADB
Note – hadbm does not add data devices to a running database instance.
Placing HADB files on Physical Disks
For best performance, data devices should be allocated on separate physical disks. This applies if there are nodes with more than one data device, or if there are multiple nodes on the same host.
Place devices belonging to different nodes on different devices. Doing this is especially important for Red Hat AS 2.1, because HADB nodes have been observed to wait for asynchronous I/O when the same disk is used for devices belonging to more than one node.
An HADB node writes information, warnings, and errors to the history file synchronously, rather than asynchronously, as output devices normally do. Therefore, HADB behavior and performance can be affected any time the disk waits when writing to the history file. This situation is indicated by the following message in the history file:
BEWARE - last flush/fputs took too long
To avoid this problem, keep the HADB executable files and the history files on physical disks different from those of the data devices.
Memory Allocation
It is essential to allocate sufficient memory for HADB, especially when it is
The HADB Node Supervisor Process (NSUP) tracks the time elapsed since the last time it performed monitoring. If the time exceeds a specified maximum (2500 ms, by default), NSUP restarts the node. The situation is likely when there are other processes in the system that compete for memory, causing swapping and multiple page faults. When the blocked node restarts, all active transactions on that node are aborted.
If Enterprise Server throughput slows and requests abort or time out, make sure that swapping is not the cause. To monitor swapping activity on Unix systems, use this command:
vmstat -S
In addition, look for this message in the HADB history files. It is written when the HADB node is restarted, where M is greater than N:
Process blocked for .M. sec, max block time is .N. sec
The presence of aborted transactions will be signaled by the error message
HADB00224: Transaction timed out or HADB00208: Transaction aborted.
Chapter 6 • Tuning for | 109 |
