ModSnmp Manual v3.07 - 6.3.3. Cache settings

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6.3.3. Cache settings

When ModSnmp reads a value from the Modbus device, it saves it in a cache. If the value is requested again (by an SNMP manager or a Modbus client) it can be returned from the cache instead of having to be fetched from the Modbus device again.

  • Lifetime. This specifies how long (in seconds) the value should be retained in the cache. If you set the lifetime to zero, the value will always be fetched from the device when it is requested.

  • Poll. If Poll is selected, ModSnmp will read the value from the device whenever its lifetime is due to expire. The value should then be available immediately when the SNMP manager requests it.

    If polling is selected, the lifetime should be large enough to avoid excessive requests being sent to the device.

  • Cache Writes. When a manager requests a value to be written to the device, ModSnmp will normally retain the value in the cache if the write is successful. The value should then be available immediately when the manager requests it, without having to read it from the device.

    Some devices have registers where the value read from the register is not the same as the value written to it. Cache Writes should be deselected for such registers.