Start/notes.ini Parameters/Server_Availability_Threshold

Server_Availability_Threshold

Parameter: Server_Availability_Threshold
Short description: Specifies the acceptable minimum level of available system resources on a server. In a cluster, this value is used to control workload distribution.

Profile

Parameter
Server_Availability_Threshold
Category
Cluster (workload balancing)
Available since
At least 9.0.1 (HCL documentation)
GUI equivalent
According to HCL, configurable in the Configuration document on the NOTES.INI Settings tab (variable SERVER_AVAILABILITY_THRESHOLD).
Possible values
Integer 0–100 (percent)

Description

According to the HCL product documentation, Server_Availability_Threshold specifies the acceptable level of available system resources for a server. By setting this value for each server in a cluster, workload distribution among the cluster members is controlled.
According to the HCL help page Setting the server availability threshold (admn_settingtheserveravailabilitythreshold_t.html): the server availability threshold specifies the lowest acceptable Server Availability Index (SAI). Approximately once per minute, Domino calculates the SAI and compares it to the configured threshold. If the SAI falls below it, the server is considered overloaded, and new sessions are redirected to other cluster members.
The default value is 0 — in HCL Domino 14.5.1 it is now also documented directly in conf_server_availability_threshold_r.html; previously the default was only documented via the help page Setting the server availability threshold.
Clarification from the HCL Domino 14.5.1 docs (verbatim):
Valid values are 0 to 100. Domino® compares this value against a server's availability index; when the availability index becomes less than the Server_Availability_Threshold value, the server becomes BUSY. A Server_Availability_Threshold value of zero (0) indicates a fully available state and workload balancing is disabled; a value of 100 indicates the server is BUSY (since the availability index can never be greater than 100) and the Cluster Manager then tries to redirect user requests to more available cluster members.
Thus: 0 = fully available, no workload balancing; 100 = the server is always considered BUSY (because the availability index can never be greater than 100), and the Cluster Manager then actively tries to redirect new user requests to other cluster members.

Example configuration

Server_Availability_Threshold=70
The value 70 used here serves as a placeholder and illustrates the format. HCL gives no specific numeric recommendation in the product documentation; the HCL help page Choosing the server availability threshold describes how the value can be determined empirically under load.

Notes & pitfalls

  • The parameter only takes effect if the server is a member of a Domino cluster.
  • Setting it to 0 (default) effectively disables threshold-based load redirection.
  • HCL warns in the help page Choosing the server availability threshold: a value that is too high can lead to unnecessary failover; a value that is too low can lead to poor performance, because users remain on an overloaded server even though another cluster member would be more suitable.
  • Configurable in the Configuration document: NOTES.INI Settings → SERVER_AVAILABILITY_THRESHOLD.

Sources (HCL Product Documentation)