eG Monitoring
 

Measures reported by HanaDeltaMrgTest

The column store uses efficient compression algorithms to keep relevant application data in memory. Write operations on the compressed data are costly as they require reorganizing the storage structure and recalculating the compression. Therefore write operations in column store do not directly modify the compressed data structure in the so called main storage. Instead, all changes are at first written into a separate data structure called the delta storage and at a later point in time synchronized with the main storage. This synchronization operation is called delta merge. The purpose of the delta merge operation is to move the data from WRITE optimized DELTA memory to READ optimized and Compressed MAIN memory or in simple terms, move the changes collected in the delta storage to the read-optimized main storage. Delta merge is a concept for in-memory column store tables only. It does not apply to tables managed in the in-memory row-store or tables managed outside of SAP HANA memory.

This test monitors the delta merge operations in the target database server and reports the number of merged tables and number of merge failed tables. In addition, this test also reports the time taken for merge operations. Using the detailed diagnosis of these measures, administrators can identify the number of merged records and thereby determine the server load along with the execution time for the merge operations. This may help them to proactively detect and resolve any performance issues before the end user is affected.

Outputs of the test: One set of results for the target database server being monitored

The measures made by this test are as follows:

Measurement Description Measurement Unit Interpretation
TotalMergedTables Indicates the total number of merged tables. Number

 
MergeFailedTables Indicates the number of tables for which the merge operation failed. Number

A low value is desired for this measure. High value is a cause for concern.

Using the detailed diagnosis of this measure, Schema name, Table name, Start time, Execution time(seconds), Merged Delta Records can be identified.

For cases where MERGED_DELTA_RECORDS becomes excessively large the trigger function for the MOTIVATION type should be reviewed and the LOAD should be analyzed for that time frame. A value of MERGED_DELTA_RECORDS = -1 suggests that no records were merged but that a compression optimization was performed.
MaxDurForMerging Indicates the maximum time taken for merging. Seconds

Using the detailed diagnosis of this measure, Schema name, Table name, Start time, Execution time(seconds), Merged Delta Records can be identified.