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Buffering

Hi all,

Can anybody please say what is the difference between

buffering allowed but switched off and

buffering switched on

Thanks in advance

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2 Answers

  • Best Answer
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    Former Member
    Posted on Aug 22, 2007 at 04:51 AM

    Hi

    The buffering status specifies whether or not a table may be buffered.

    This depends on how the table is used, for example on the expected volume of data in the table or on the type of access to a table. (mainly read or mainly write access to the table. In the latter case, for example, one would not select buffering).

    You should therefore select

    - Buffering not allowed if a table may not be buffered.

    - Buffering allowed but not activated if buffering is

    principally allowed for a table, but at the moment no buffering

    should be active. The

    buffering type specified in this case is only

    a suggestion.

    - Buffering allowed if the table should be buffered. In this

    case a buffering type

    must be specified.

    Single-record buffering

    With this kind of buffering, only the records of a table which are actually accessed are loaded into the buffer.

    This kind of buffering requires less storage space in the buffer than full buffering. However, greater organization is necessary and considerably more database accesses are necessary for loading.

    If an as yet unbuffered record is accessed using SELECT SINGLE, a database access occurs to load the record. If the table does not contain a record for the specified key ('no record found'), this record is noted as nonexistent in the buffer. If a further attempt is made to access this record using SELECT SINGLE, a renewed database access can be avoided.

    When should single-record buffering be selected?

    For large tables where there are frequent single-record accesses (using SELECT SINGLE ...). The size of the records being accessed should be between 100-200 KB.

    For comparatively small tables for which the access range is large, it is normally advisable to opt for full buffering. Only one database access is required to load such a table for full buffering, while single-record buffering calls for a very large number of table accesses.

    Generic buffering

    In a read access to a record of a generically buffered table, all the records whose left-justified part of the key (generic area) corresponds are loaded into the buffer.

    If this type of buffering is selected, the generic area must be defined by specifying a number n of key fields. The first n key fields of the table then define the generic key.

    The number of key fields to be entered must lie between 1 and the number of key fields -1. For example, only values between 1 and 5 are permitted for a table with 6 key fields. The client field is included here.

    When should generic buffering be selected?

    A table should be buffered generically if usually only certain areas of the table are required. The individual generic areas are treated like independent tables that are fully buffered. Refer also to the text on complete buffering.

    The generic key area should be selected so that the generic areas are not too small to prevent too may generic areas being produced. If there are only a few records for each generic area, it is more efficient to use full buffering.

    Generic buffering only makes sense if the table is accessed by a specified generic key. If, when an access takes place, a field of the generic key is not supplied with a value, the buffer is ignored and the records are read directly from the database.

    Language-specific tables are an example of good use of generic buffering (with the language key field as generic key area).

    Full buffering

    With full buffering, either the complete table or none of the table is in the buffer. If a read access is made to a record, all records of the table are transferred to the buffer.

    When should you select full buffering?

    For tables up to 30 KB in size. If a table is accessed frequently, but all accesses are read accesses, this value can be exceeded.

    For larger tables where large numbers of records are frequently accessed. However, if the application program is able to formulate an extremely selective WHERE condition using a database index, it may be advisable to dispense with full buffering.

    For tables with frequent accesses to data not contained in the table. Since all records are contained in the buffer, a quick decision can be made as to whether or not the table contains a record for a specific key.

    When considering whether a table should be fully buffered, you should take three aspects into account: the size of the table, the number of read accesses, and the number of write accesses. Tables best suited to full buffering are small, frequently read, and rarely updated.

    Regards

    Ravish

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    Reward if useful</b>

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  • Posted on Aug 22, 2007 at 04:51 AM

    HI,

    -<b> Buffering allowed but not activated</b> if buffering is

    principally allowed for a table, but at the moment no buffering

    should be active. The

    buffering type specified in this case is only

    a suggestion.

    <b>- Buffering allowed</b> if the table should be buffered. In this

    case a buffering type

    must be specified.

    In the first case you are giving a suggestion that the table can be buffered but at this ponit of time you dont want to activate it and when someone wants to activate it he can use the bufferig type mentioned as a suggestion.

    Regards,

    Sesh

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