PowerExchange Interfaces for PowerCenter

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Configuring PWX Latency and Real-Time Flush Latency

The following table describes the optional flush latency connection attributes:

Connection Attribute	Change or Real Time	Description
Real-Time Flush Latency in milli-seconds	Real Time	The number of milliseconds that must elapse before PWXPC sends a commit request to PowerCenter. When this period elapses, PWXPC continues to read the changes in the current UOW until it reaches the end of the UOW. Then PWXPC sends a commit request to PowerCenter so that the data can be committed to the targets. Valid values: -1 . Disables this attribute. 0 to 86400 . Specifies the number of milliseconds that must elapse before PWXPC sends a commit request to PowerCenter. If you specify a value from 0 through 2000, PWXPC uses 2000 milliseconds (2 seconds). Default is 0.
PWX Latency in seconds	Real Time	The maximum number of seconds that PowerExchange on the source machine waits for more change data before it flushes data to PWXPC on the PowerCenter Integration Service machine. Default is 2.

When a CDC session begins, PWXPC passes the

PWX Latency in seconds

attribute value from the connection to the PowerExchange Listener and requests change data from the change stream. The PowerExchange Listener uses this latency value as the Consumer API (CAPI) interface timeout value on the source machine. PowerExchange issues the following message on the source machine to identify the CAPI interface timeout value:

PWX-09957 CAPI i/f: Read times out after <number> seconds

If you select the

Retrieve PWX Log Entries

attribute on the connection, PWXPC also writes this informational message to the session log.

PowerExchange reads change data into a buffer on the source machine. When the one of the following conditions occur, PowerExchange flushes the buffer that contains the change data to PWXPC on the PowerCenter Integration Service machine:

The buffer becomes full.

A commit point occurs.

The

PWX Latency in seconds

interval, or CAPI interface timeout, expires.

The CAPI interface timeout also affects the speed with which PWXPC processes stop requests from PowerCenter. PWXPC must wait for PowerExchange to return control to it before it can handle a stop request.

After PowerExchange flushes change data to PWXPC, PWXPC provides the change data to the source qualifier and the

Real-Time Flush Latency

interval begins. After the

Real-Time Flush Latency

interval expires and PWXPC reaches a UOW boundary, PWXPC sends a commit request to PowerCenter and writes the following message to the session log:

[PWXPC_10082] [INFO] [CDCDispatcher] raising real-time flush with restart tokens [restart1_token], [restart2_token] because Real-time Flush Latency [milliseconds] occurred

For example, if the value for real-time flush latency interval is 10 seconds, PWXPC sends a commit request to PowerCenter for all complete UOWs after 10 seconds elapses and the next UOW boundary is met.

The lower you set the

Real-Time Flush Latency

interval, the faster change data is committed to the targets. If you require the lowest possible latency for applying changes to targets, specify a low value for the

Real-Time Flush Latency

interval.

When you specify low flush latency intervals, the CDC session might consume more system resources on the source, PowerCenter Integration Service, and target systems for the following reasons:

PowerExchange returns more frequently to PWXPC. As a result, PowerExchange passes fewer rows to PWXPC on each iteration and consumes more resources on the source machine.

PowerCenter commits change data to the targets more frequently. As a result, more resources are consumed on the PowerCenter Integration Service and target machines.

When you set the flush latency intervals, balance performance and resource consumption with latency requirements.

To control commit processing on the target, you can use the

Real-Time Flush Latency

attribute in conjunction with the

Maximum Rows Per commit

and

UOW Count

connection attributes.

CDC Application Connection Attributes

Commit Processing for CDC Sessions

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