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Difference between Sequential Read and Direct Read

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Difference between Sequential Read and Direct Read
Stechies

Sequential Read vs Direct Read

It is a very common misconception that "sequential reads in SM50 means that a full table scan is executed and an index is not used". The correct definition/concept is:

Direct read

The term "Direct read" refers to accesses in which a maximum of one line is returned by the database. This includes summarization queries such as SELECT COUNT and fully-qualified primary key accesses.

Sequential Read

A "Sequential Read" refers to all other read database accesses, in which there may be more than one line returned. It is true that the term "Sequential read" is a little deceptive since it implies that blocks are always read sequentially (as in a full table scan). In reality, however, when you perform a trace on these queries you will see that index is used in most cases.

So, "Direct read" and "Sequential read" in SM50 are worthless for a performance analysis. It only shows that the processes are running and processing one of the queries directed at the database interface.

For expensive SQL statements analysis, "Reads/User Calls" value (TCODE BACOCKPIT or ST04OLD) is an indication. If this value is above 15, the SQL statements should be checked in detail.

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Comments

  • 27 Feb 2014 3:14 am

    Thanks...Is it possible to check in which program do we have sql query problems?

  • 24 Jun 2014 8:51 am

    @Boudhayan Ghosh: Yes, in ST04 -> sql cache, when You will find most expensive statement, just double click on it and on the next screen just press source.

    Hope it helps!

    Kind regards

    Paweł

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