The concept of “throw-away” in performance tuning
Posted: Tue Jan 28, 2025 3:34 am
As already mentioned, “throw-away” refers to records that have been read from the database but do not influence the result of a query in any way. Minimizing the “throw-away” is a basic principle of performance tuning [1] (section 12.1.2.). The concept is intuitively plausible, since a record that is retrieved but not used certainly represents unnecessary effort. A common use is the application of “throw-away” in the optimization of index definitions, as illustrated in Fig. 1.
Here we see the essential part of a SQL Monitor evaluation. We see that 175k records are found via index access. When the table is accessed, only one record albania telegram screening remains. This means that there is an additional filter on the table that dramatically reduces the number of records. This filter is not supported by the index.
All we have to do is look up the columns of the filter in the execution plan and add them to the index (note: of course we also have to make sure that the additional columns in the index are used frequently and not just by this one query). This way, the records would be filtered out in the index and not only when the table is accessed.
Here we see the essential part of a SQL Monitor evaluation. We see that 175k records are found via index access. When the table is accessed, only one record albania telegram screening remains. This means that there is an additional filter on the table that dramatically reduces the number of records. This filter is not supported by the index.
All we have to do is look up the columns of the filter in the execution plan and add them to the index (note: of course we also have to make sure that the additional columns in the index are used frequently and not just by this one query). This way, the records would be filtered out in the index and not only when the table is accessed.