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HOW TO: Calculate PowerExchange Oracle CDC Log Read Rate

This document describes how to calculate the rate at which PowerExchange Oracle Express Logger reads the Oracle Redo Logs. This is important to know so that it can be determined if the Logger will be able to keep pace with the rate at which data is written to the Redo Logs.

Calculation Information

The calculation requires information garnered from messages that are output by the PowerExchange Logger process, pwxccl. The messages are included in a detail.log file or a file whose name starts with PWXCCL. The LOGPATH statement in the dbmover configuration file used to start the PowerExchange Listener and Logger identifies the directory where the message log files are located.

If there is not a TRACING statement in the dbmover configuration file, the messages will be in a file named detail.log in the path specified in the value specified in the LOGPATH statement.  If a TRACING statement is specified, the messages will appear in a file name that begins with PWXCCL.

The messages used are PWX-36144 and PWX-36169.  The PWX-36144 message specifies when the Logger begins reading an Oracle Redo log. The PWX-36169 message specifies when the Logger has completed reading a Redo Log.  The PWX-36169 message also states the number of blocks that were read. Both messages include the SEQ # of the Log that was being read.  It is important that both messages refer to the same SEQ #.

181024 110149 LNX64 3 PWX-36144 ORAD Info Mbr 1: Reader processing current Log

                      file +PROA11RECO/proa11/onlinelog/group_12.261.839411135,

                      SEQ 1076233.


181024 110311 LNX64 3 PWX-36169 ORAD Info Mbr 1: Reader done processing log

                      Sequence 1076233. Last SCN 7539153736775. Last SCN Time

                      10/24/2018 11:02:56. Blocks processed 917884.


To complete the calculation, you will need to know the block size of the files.  This is determined by the operating system. On Linux or Unix this value can be determined by issuing the command “df .” after issuing a cd command to the directory that contains the Oracle Redo logs.


bash-4.2$ pwd


bash-4.2$ df .

1K-blocks     Used                  Available     Use% Mounted on

/dev/sda3      203278360 95830632 107447728  48% /



The formula to calculate the rate at which the Logger reads the Redo logs in GB per hour is as follows:

((blksize/1GB) * 3600) * # blocks / # seconds = N GB/hr

1GB = 1073741824 bytes

(GB/hr factor) * # blocks / # seconds = N GB/hr

The GB/hr factor is (blksize in bytes/1Gb * 3600 secs/hr).  For the standard block size of 1024 this is 0.003443.

For the example PWX-36144 and PWX-36159 messages listed above the number of seconds is 82 (11:03:11 – 11:01:49).  The number of blocks processed is 917884.

0.003443 * 917884 blocks / 82 seconds = 38.43Gb/hour.


More Information


PowerExchange CDC Guide for Linux, UNIX and Windows "Chapter 7: Express CDC for Oracle"


Applies To
Product: PowerExchange
Problem Type: Performance
User Type: Administrator; Developer
Project Phase: Configure
Product Version:
Database: Oracle
Operating System: Linux; UNIX
Other Software:
Velocity Phase:
Velocity Packages:
IPS Document Type: Tips-Tricks-Examples
Last Modified Date: 8/12/2019 2:37 AM ID: 566044
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