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CDC Output Does not Keep up with Transactions, CDC replication is slow

Technote (troubleshooting)


You create an application to capture transactions on your IBM Informix Server. Your application is built using the Informix CDC (Change Data Capture) API. You note that transaction data returned by the application lags significantly behind the actual data changes.

CDC replication is slow


The data recorded by a CDC application returns transactions after they enter the transaction log files and in the order they enter the files. The data will not be visible to the CDC application until it is flushed from the logical log buffer.
Note: You can see this behavior using the demonstration program found in the $INFORMIXDIR/demo/cdc directory with 11.7 and 12.1 engines.

Resolving the problem

Here are the five events that cause the current logical-log buffer to flush:

  • The current logical-log buffer becomes full.
  • A transaction is prepared or committed in a database with unbuffered logging.
  • A nonlogging database session terminates.
  • A checkpoint occurs.
  • A page is modified that does not require a before-image in the physical log.

Related information

CDC sample program

Historical Number


Document information

More support for: Informix Servers

Software version: 11.7, 12.1

Operating system(s): AIX, HP-UX, Linux, OS X, Solaris, Windows

Reference #: 1626242

Modified date: 14 February 2014

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