Configure transaction and subscription settings

You can set the following transaction and subscription settings:

Transaction to Subscription Ratio

This parameter controls the ratio of transaction to subscription messages in a Communication Driver at the time when several transaction messages are pending. This value is the maximum number of transaction messages sent before sending a subscription message. The second half of the ratio is always 1. The default ratio is 2 transaction messages to 1 subscription message (2:1).

Transactions have a higher priority than subscriptions. If only one transaction message is pending, that message is sent first no matter how many subscription messages are due to be sent. If one or more transactions generate several transaction messages, this ratio applies to the number of generated transaction messages. This ratio ensures that a certain amount of subscription activity is guaranteed even in a transaction overloaded state. The value sets the number of allowed transaction messages to be arbitrated on the protocol before evaluation of due subscription messages is enforced. If subscription messages are due, one of them is sent before sending transaction messages again.

Transaction Message Timeout

This parameter sets the timeout for transactions (read/write/refresh/property) per message. The value is an integer representing the timeout in milliseconds per transaction message. Default is 60000 (corresponds to the default ValidDataTimeout in legacy I/O servers). A properly operating Communication Driver should never encounter this timeout because a transaction will always be completed by the protocol engine (successful or not). This timeout only prevents a client from hanging in a transaction forever if, for some reason, the transaction messages are never scheduled until completion. The timeout is specified on an individual message level. It is not the maximum amount of time a transaction can take. It is the maximum amount of time between message updates within a transaction. The timeout has to be set in such a way that under no circumstances can data acquisition on an individual message take longer than this timeout. The time it might take for a transaction containing several messages theoretically can be multiples of this timeout.

Diagnostic Backlog Size

Controls the maximum number of transactions displayed in the Transactions diagnostic node. The diagnostic backlog size parameter does not affect the number of transactions allowed by the Communication Driver. It strictly affects the number of transactions shown in the Transactions node.