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Background documentation Buffering Hints  Locate the document in its SAP Library structure

 

To decide for or against buffering a table, you should consider the following:

      Is the delay in visibility, that may arise between different cluster nodes (within a buffer synchronization period of one minute by default), acceptable?

      Is the table mostly read or frequently modified?

      How large is the buffered part (the generic region) of the table?

If in doubt, use the following guidelines:

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       1.      You should buffer tables that are mostly read and rarely modified. Buffering is recommended for small tables. Large tables are usually indexed by the database, whereas the table buffer does not use indexes.

       2.      Choose the buffer granularity of the table carefully. Important parameters are:

       The expected size of the table

Full buffering is not recommended for large tables.

       Read accesses

To access the buffer, your query has to provide the defined key range – that is, the generic key. A query that does not specify the generic key range, bypasses the buffer. The granularity (the partitioning) of the table buffer should match the keys provided by the application that accesses the table.

       Non-existent data

When a WHERE clause specifies a generic area, which does not contain any records, a “not found” entry is stored for this area. From the single records buffering perspective, this means that each key value that is not in the table, appears as “not found” in the table buffer when a query tries to retrieve the corresponding record. The potential overload is avoided when you use full buffering. We recommend that you use full buffering for empty or small tables.

       3.      It is important to choose an appropriate generic key with respect to the table size. A short generic key may lead to a large number of buffered records. A large generic key usually means a small number of buffered records, but then the queries bypass the buffer more often and the buffering is not efficient.

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