Allbase/SQL uses sorting in several ways:
When creating an index on a table that contains data.
When processing a query that contains an ORDER BY, DISTINCT, UNION,
or GROUP BY clause.
When processing a join query with the sort/merge join algorithm.
Sorting operations require both disk space and CPU time, so they often
raise performance issues. Space for sorting may be required in
temporary files
which can be in the current group or directory or in TempSpaces you
define for the purpose. You can avoid the use of temporary files
at run time by creating an index on the sort key. In many cases,
the index can be used to carry out the sort.
Space is also needed for the temporary storage
of sort output. This space is allocated in the SYSTEM
DBEFileSet, which must have enough TABLE or MIXED DBEFile space to
accomodate each query result.
Performance issues in sorting are
discussed in more detail in the section "Sorting Operations" in the
"Guidelines on System Administration" chapter.
