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BTREE structure features for data processing patterns
The factor having the greatest effect on data processing efficiency is the I-O frequency. The BTREE structure has the
following features:
· In the following cases, the I-O frequency depends on the depth of the index part. The range of index key
values is specified, or only the values of the leftmost column of an index key consisting of a group of columns
is specified in the data processing.
· Otherwise, the relevant index is not used.
BTREE structure page size specification
In a BTREE structure, the page size can be independently specified for the index part and the data part. The data part
page size is specified by the PAGESIZE1 option of the DSO definition. The index part page size is specified by the
PAGESIZE2 option.
When specifying the page size, carefully consider the following points:
· The group of correspondence information values for index keys and base table data must fit as two records.
These records must be in a single page of the index part and data part.
· If the amount of data that fits in the index part and data part is small, the page utilization rate (data storage
rate) decreases. To increase the page utilization rate, specify a page size having a surplus area.
· To fit a maximum number of data entries in a single page of the data part, carefully consider and set the page
splitting points. Frequent page splitting decreases the processing efficiency.
Considerations when adding indexes
The user can add multiple indexes to a single base table. By adding indexes, the user increases the processing
efficiency for searches. However, in the following cases, since processing for upgrading all related indexes is
performed, overall processing efficiency may decrease:
· Application program processing updates values of columns for which indexes have been added or base table
data correspondence information.
· Application program processing primarily performs insertions and deletions.
4.3 Allocating Space
This section gives details on the following topics related to the allocation of database space for DSIs:
· Formats for associating storage structures and database spaces
· Considerations when allocating space
4.3.1 Formats for associating storage structures and database spaces
Each type of storage structure consists of several components. When database space is allocated to storage
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