# Time Complexity in ABAP

One of the key operations in ABAP is the READ statement, which is used to read data from internal tables. In this blog, we will discuss the time complexity of READ statements with all types of internal tables in ABAP.

The same applies for the modern ABAP expression

``wa = itab[ col1 = … col2 = … ].``

Firstly, let us understand what time complexity means. Time complexity refers to the amount of time taken by an algorithm to solve a problem as a function of the size of the input. In other words, it measures the number of steps an algorithm takes to solve a problem, as the size of the problem increases.

Internal tables are data objects used for storing data within an SAP program. There are three types of internal tables in ABAP: standard, sorted, and hashed.

1. Standard internal tables

A standard internal table is the most basic type of internal table in ABAP. The time complexity with a standard internal table is O(n), where n is the number of records in the internal table. This means that the time taken by the READ statement increases linearly with the number of records in the internal table. Therefore, it is important to limit the number of records being read to improve performance.

1. Sorted internal tables

A sorted internal table is an internal table that is sorted on one or more key fields. The time complexity with a sorted internal table is O(log n), where n is the number of records in the internal table. This means that the time taken by the READ statement increases logarithmically with the number of records in the internal table. Therefore, using a sorted internal table and a binary search can significantly improve the performance of READ statements.

1. Hashed internal tables

A hashed internal table is an internal table that uses a hashing algorithm to access its records. The time complexity with a hashed internal table is O(1), which means that the time taken by the READ statement is constant, regardless of the number of records in the internal table. This makes hashed internal tables ideal for large datasets where performance is critical.

The transaction code SE30 can be used to analyze the performance of ABAP programs, including READ statements. SE30 measures the runtime of an ABAP program, including the time spent on each individual statement, function call, and subroutine. Using SE30, developers can identify performance bottlenecks and areas for optimization, such as replacing standard internal tables with sorted or hashed internal tables.

The transaction code STAT is another powerful tool in SAP that allows users to analyze the performance of ABAP programs. STAT generates detailed reports that can help identify performance bottlenecks and areas for optimization, allowing developers to improve the performance of their ABAP programs. STAT can be used for individual programs, as well as for entire systems, making it an essential tool for SAP developers and administrators.

In conclusion, the time complexity of READ statements with internal tables in ABAP depends on the type of internal table being used. Standard internal tables have a time complexity of O(n), sorted internal tables have a time complexity of O(log n), and hashed internal tables have a time complexity of O(1). By selecting the appropriate type of internal table and using performance analysis tools like SE30 and STAT, developers can optimize READ statements to improve the performance of SAP solutions.

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Many inexperienced ABAP developers continue using standard tables because it's the default and shortest way of typing (i.e. when "DATA ... TYPE TABLE ..." is used, it means "type standard table", sorted and hashed categories require explicit mention), and also most of code snippets in the Web use standard tables.

itab[ ... ] is named a Table Expression and should be preferred to READ TABLE itab WITH KEY ... because it's shorter and required when using Constructor Expressions (exist since the old ABAP 7.40 version). But "newbies" should be aware of the big difference concerning the exception if no line is found and sy-subrc/sy-tabix are not filled, line_exists or assign or line_index must be used instead.

Newbies should stop using standard tables (unless rare cases when there's no other choice). This blog post by Jerry (2015) goes straight to the point concerning read and insert (memory usage is from me):

• Standard (without binary search) = slow read (O(n)), fast insert, little memory overhead
• Sorted = fast read (O(log n)), less fast insert, small memory overhead
• Hashed = very fast read (O(1)), less less fast insert, medium memory overhead

NB: when standard tables cannot be avoided, sort and binary search can be used to mimic internal tables of type sorted.

There is also this blog post by Siegfried (2007).

SAT is the modern name of SE30. It's best to use SAT to avoid confusion in case people are working on old ABAP versions.

STAT doesn't exist. I guess you mean ST03N or STAD. They are just to be used during campaigns to improve SAP system overall performance to identify which programs are slow (it's usually run by administrators). You need to use SAT to understand which internal tables are concerned.

Last but least, ABAP developers should all read and master the official ABAP documentation - itab - Performance Notes.

Kunal Sahi
Blog Post Author

Thank you for sharing your thoughts on the usage of standard tables and providing insights into different table types and their performance characteristics. You make some valid points regarding the preferences and considerations for choosing the appropriate table type in ABAP development.

You also rightly emphasize the importance of referring to the official ABAP documentation, particularly the performance notes for internal tables. Mastering the official documentation is essential for developers to stay up to date with the latest features, guidelines, and optimizations provided by SAP.