Measures reported by HanaLogSegTest

The database manages its transaction log in so called log segments. A log segment is a file of a configuration-defined size (default: 1 GB) which holds the transactions in a range of transaction numbers. All segments together make up the log area. Once a log segment reaches its configuration-defined limit, a new segment is opened by the database as long as there is enough space left in the configuration-defined size of the log area as a whole. There are different states for log segment, that includes,

• Writing: The log segment is currently being written.

• Closed: The log segment is closed, not backed up and is still required for restart.

• Truncated: The log segment is not required for restart, but has not been backed up.

• BackedUp: The log segment has been backed up, but is still required for restart.

• Free: The log segment has been backed up, it is not required for restart and can be reused.

• Formatting: The log segment is being formatted and not yet used.

• RetainedFree: The log segment has been backed up and is not required for restart, but is required to resync the system replication sites.

• Peallocated: The log segment has been preallocated, but never used.

Once a log segment is full and a new one is created, the automatic log backup mechanism is triggered by the database. This cannot be prevented and is a forced behaviour in order to ensure that the database does not have to stop executing transactions due to lack of space in the transaction log. Seen from a backup perspective, this means that a log backup always occurs automatically when a log segment is complete. The database also tries to perform a log backup if the size of the log area as a sum (all transaction logs since the last savepoint) grows over a defined threshold. This is a rather severe status because if the log backups frequently fail in this case, the database will soon stop to execute database transactions (at least writing transactions) and business will be affected similar to a downtime. Hence, it is very crucial to monitor the growth of log segments in size and alerts administrators before any critical situation, such as log area grows over the defined threshold, occurs.

This test monitors all the log segments files in the log volume of the target database server and reports the total size and used size of the log segment and also indicates the percentage of free space in the log segment. Detailed diagnosis of the test clearly indicates the state of the log segment, which helps administrators effectively track log segment growth and initiate control measures before it adversely affects the database performance.

Outputs of the test: One set of results for every log segment files in the target database server being monitored

Descriptor: Log Segment

The measures made by this test are as follows: