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SAP Buffering
When accessing database tables using Open SQL, SAP buffering is effective as standard if it is activated for the corresponding database table. It can be explicitly deactivated using the addition BYPASSING BUFFER of the statement SELECT.
In addition to the explicit specification of BYPASSING BUFFER, SAP buffering can also be bypassed implicitly by some variants of the Open SQL statements, as the corresponding operation can only be executed in the database and not in the SAP buffer.
The following Open SQL statements implicitly bypass the SAP buffer and access the database tables directly:
SELECT with the addition FOR UPDATE,
Access to a table using single-record buffering without selecting a single record using SINGLE SELECT or by specifying the primary key in the WHERE condition (this behavior depends on the current implementation of the database interface and may be different in future releases).
SELECT with the addition DISTINCT,
SELECT with aggregate expressions,
Open SQL statement with the addition CLIENT SPECIFIED, without specification of the client ID in a WHERE condition,
SELECT with JOIN expressions
Access to a generically buffered area without full specification in a WHERE condition
Open SQL statements with IS [NOT] NULL in the additions WHERE and HAVING,
Use of a subquery in a WHERE condition,
SELECT with the addition GROUP BY,
SELECT with the addition ORDER BY, whereby the sort key is not the primary key.
Note
Bypassing the SAP buffer with the above additions is a means to increase the performance when accessing buffered database tables. To explicitly bypass the SAP buffer in the SELECT statement, always use the addition BYPASSING BUFFER instead of the implicit behavior of the additions stated above.
Reduce the database load wherever possible
Saving database in local buffers (see SAP buffering) can save considerable time in client-server environments, as the access time via the network is considerably higher than access time via a locally buffered table.
The SAP buffering is switched off:
When you use SELECT FOR UPDATE or SELECT DISTINCT in the SELECT clause,
When you use BYPASSING BUFFER in the FROM clause,
When you use JOINs and subqueries (subqueries),
When you use ORDER BY f1 f2 ... in the ORDER-BY clause.
When you use aggregate functions in the SELECT clause.
When you use IS [NOT] NULL in the WHERE condition.
You cannot process a query in the SAP buffer if the generic key section is not specified in the WHERE condition
Avoid re-reading the same data.
Before you change a table using DELETE, INSERT or UPDATE, you should check whether you need to read entries using SELECT.
If you want to sort data, it is more efficient to read it into the internal table and sort it using SORT than to use the ORDER-BY clause, where the sort is not supported by an index.
Check whether you can delete duplicates using the variant DELETE ADJACENT DUPLICATES FROM itab instead of using SELECT DISTINCT.
You should use logical databases if possible.
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