(B)0index-storage-clause =

  STORE qw> index-within-clause qqqqqqqqqqqqqqqqqqqqqqqqqqwqk
         m> USING qw> field-name qw> index-within-clause qj x
                   mqqqqq , <qqqqqj                         x
   lqqqqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj
   mqwqqqqqqqqqqqqq>qqqqqqqqqqqqqqwqq>
     m> default-threshold-clause qj

    Allows you to specify a storage map definition for the index. You
    can use the index-storage-clause only in a multifile database.
    This clause allows you to specify which storage area files will
    be used to store the index entries:

    o  All index entries can be associated with a single storage
       area.

    o  Index entries can be systematically distributed, or
       partitioned, among several storage areas by specifying upper
       limits on the values for a key in a particular storage area.

    If you omit the storage map definition, the default is to store
    all the entries for an index in the main RDB$SYSTEM storage area.

    You should define a storage area for an index that matches the
    storage map for the relation with which it is associated. In
    particular, under the following conditions, the database system
    will store the index entry for a row on or near the same data
    page that contains the actual row:

    o  The storage areas for a relation have a mixed page format.

    o  You specify an identical storage clause for the index as
       exists in the storage map for the relation.

    o  The storage map for the relation also names the index in the
       PLACEMENT VIA INDEX clause.

    Such coincidental clustering of indexes and rows can reduce
    input/output operations. With hashed indexes and coincidental
    clustering, the database system can retrieve rows for exact match
    queries in one input/output operation.

    For sorted indexes, specifying an identical storage map reduces
    input/output contention on index nodes.