SDS_FLOW_CONTROL configuration parameter

Specifies when flow control occurs in a high-availability cluster that contains at least one shared-disk (SD) secondary server.

onconfig.std value
SDS_FLOW_CONTROL 0
values
0 = Flow control is activated when the difference between the current log position and the most recent acknowledged log exceeds 12 times the size of the log buffer.

-1 = Flow control is disabled. Disabling flow control might lead to wrapping of the log files and the loss of data.

start_value,end_value = The start_value and end_value determine the amount of lag between the current log position and the last acknowledged log page. The start_value must be greater than the end_value. Values must include one of the following units:
  • K (Kilobytes)
  • M (Megabytes)
  • G (Gigabytes)
For example, setting SDS_FLOW_CONTROL 128M,100M starts flow control when the lag between the logs is 128 MB, and stops flow control when the lag has dropped to 100 MB.
takes effect
After you edit your onconfig file and restart the database server.
When you reset the value dynamically in your onconfig file by running the onmode -wf command.

Usage

Flow control provides a way to limit log activity on the primary server so that SD secondary servers in the cluster do not fall too far behind on processing transactions. When flow control is enabled, and when the difference in log size between the current log position and the last acknowledged log page exceeds thestart_value, then log activity on the primary server becomes restricted. Users connected to the primary server may experience slower response time when flow control is active. Flow control is started when the lag between the logs is greater than the start_value and stops flow control when the log lag has dropped to thestop_value.

You set the SDS_FLOW_CONTROL configuration parameter on the primary server only. All SD secondary servers in the cluster are affected by the SDS_FLOW_CONTROL configuration parameter. Logs are always sent to the SD secondary server in the order in which they were received.


Copyright© 2019 HCL Technologies Limited