Progress After-Image Log Activity Test

The after-imaging feature lets you recover a database that was damaged when a failure caused the loss of the database or primary recovery (before image) area. When you enable after-imaging, the database engine writes notes containing a description of all database changes to the after-image (AI) files. The AI files with the roll-forward recovery process can be used to restore the database to the condition it was in before the database was lost, without losing completed transactions that occurred since the last backup. If the After-image files are not written with the changes to the database changes then and there, a considerable amount of data may be lost and hence, the database cannot be recovered completely. Also, if the buffer is not available on the after-image file, then, the processes that are initiating the writes on the file may be made to wait for a longer duration. This may also result in an increase in the wait time of the physical I/O on the file and eventual data loss if the database fails during the waiting period of the processes. Therefore, it is necessary to maintain a close watch on the writes to the AI file. The Progress After-Image Log Activity test helps administrators in monitoring the writes on the AI file.

By constantly monitoring the writes to the after-image file, this test reports the total number of writes to the file, the writes that were performed by the after-image writer and the number of times a process had to wait for the buffer in the AI file to write etc. This way, administrators can determine how well the writes were performed on the AI file and take precautionary steps to avoid data loss completely.

Target of the test : A Progress Database server

Agent deploying the test : An internal agent

Outputs of the test : One set of results for every Progress database server that is being monitored

Configurable parameters for the test
Parameter Description

Test Period

How often should the test be executed

Host

The IP address of the Progress database server.

Port

The port number on which the database server is listening. By default, this is NULL.

Database Name

Specify the name of the Progress database instance that is to be monitored.

Username

In order to monitor a Progress database instance, a special database user account has to be created in every Progress database instance that requires monitoring. This special user needs to be granted a set of privileges. To know how to create the database user and grant the required privileges, refer to Pre-Requisites for monitoring the Progress database. Specify the name of such a user in this text box.

Password

The password of the specified Username.

Confirm Password

Confirm the password by retyping it here.

Measurements made by the test
Measurement Description Measurement Unit Interpretation

Total writes

Indicates the total number of writes to the after-image file per second during the last measurement period.

Writes/Sec

The value of this measure includes the value of the AIW writes measure too.

AIW writes

Indicates the total number of writes performed by the after-image writer per second during the last measurement period.

Writes/Sec

 

AIW write hit ratio

Indicates the ratio between the writes performed by the after-image writer and the total writes to the after-image file during the last measurement period.

Percent

 

Buffer busy waits

Indicates the number of times Buffer Busy waits have occurred on the after-image file when a block in the buffer cache was being held by the after-image writer during the last measurement period.

Number

The Buffer Busy wait happens when a session wants to access a database block in the buffer cache but it cannot because the buffer is busy. Another session is modifying the block and the contents of the block are in flux during the modification. The two main cases where this wait can occur are:

  • Another session is reading the block into the buffer
  • Another session holds the buffer in an incompatible mode to our request

If too many buffer busy waits occur on the database, then it often indicates that the physical writes to the after-image file is taking longer to complete.

Committed waits

Indicates the rate at which commit waits have occurred on the after- image file when a block in the buffer cache was being held by the After image writer during the last measurement period.

Records/sec

 

Waits for no buffer

Indicates the number of times a process had to wait since the buffer was not available in the after-image file during the last measurement period.

Number

 

Log size

Indicates the current size of the after-image log file.

MB

 

Growth rate

Indicates the rate at which the size of the after-image log file had grown during the last measurement period.

MB/sec

A consistent increase in the value of this measure is a cause for concern, as it indicates a steady growth in after-image log file size.