(B)0[mmap-storage-clause =
[4mSTORE[m qw> map-within-clause qqqqqqqqqqqqqqqqqqqqqqqqqqwqk
m> [4mUSING[m qw> field-name qw> map-within-clause qj x
mqqqqq , <qqqqqj x
lqqqqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqqqqqqqqqj
mqwqqqqqqqqqqqqq>qqqqqqqqqqqqqqwqq>
m> default-threshold-clause qj
Used to define a storage map. This clause lets you specify which
storage area files will be used to store rows from the relation:
o All rows of a relation can be associated with a single storage
area.
o Rows of a relation can be randomly distributed among several
storage areas.
o Rows of a relation can be systematically distributed, or
partitioned, among several storage areas by specifying upper
limits on the values for a column in a particular storage
area. This is called horizontal partitioning.
If you omit the storage map definition, the default is to store
all the rows for a relation in the main RDB$SYSTEM storage area.
1 – map-within-clause
(B)0[mmap-within-clause =
[4mWITHIN[m qwq> area-name qwqqqqqqqqqqqqqq>qqqqqqqqqqqqqqqwqk
x m> [4mWITH[m [4mLIMIT[m OF qw> literal qwj x
x mqqqq , <qqqj x
xlqqqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqqj
xmwqqqqqqqqqqqqqqqqqqqqqq>qqqqqqqqqqqqqqqqqqwqwqk
x mq> [4mFOR[m qwqwqw> rel-name qwqqqqqqqqqqqqqqqu x x
x x x mqqqq , <qqqqj x x x
x x mw> relation-name.field-name qwj x x
x x mqqqqqqqqqqqq , <qqqqqqqqqqqqj x x
x mqqqqqqqqqqqq , <qqqqqqqqqqqqqqqqqqj x
x lqqqqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqj
x mqwqqqqqqqqqq>qqqqqqqqqqwqqwqqqqqqqqq>
x mq> threshold-clause qj x
mqqqqqqqqqqqqq ; <qqqqqqqqqqqj
1.1 – area-name
The name of the storage area you want records stored in. You
must have defined this storage area with either the DEFINE
DATABASE statement or the DEFINE STORAGE AREA clause of the
CHANGE DATABASE statement before you refer to it in the store
clause.
1.2 – WITH_LIMIT_OF
The maximum value for the index key that will reside in the
specified storage area.
The number of literals in this clause must be the less than or
equal to the number of fields in the USING clause. Repeat this
clause to partition the index entries among multiple storage
areas.
When you define a multisegmented index using multiple keys and
use the STORE USING...WITH LIMITS clauses, if the values for the
first key are all the same, then set the limit for the first key
at that value. By doing this, you ensure that the value of the
second key determines the storage area in which each record will
be stored.
Note that the last storage area you specify CANNOT have a WITH
LIMIT OF clause associated with it.
If you change the limits for a storage area, records that were
already stored in the area are not moved according to the new
limit clause. However, new records will be stored into the
relation according to the new limits you specify.
1.3 – rel-name
The name of the relation whose segmented strings you want to
store in the specified storage area. If you want to store the
segmented strings of more than one relation in the storage area,
separate the names of the relations with commas.
1.4 – relation-name.field-name
The name of the relation and segmented string field that you want
to store in the specified storage area. If you want to store more
than one segmented string field in the storage area, separate the
list items with commas.
1.5 – threshold-clause
(B)0[mthreshold-clause=
qq> [4mTHRESHOLDS[m ARE qqqqqqqqqqk
lqqqqqqqqqqqqq<qqqqqqqqqqqqqj
mq> ( qq> val1 qwqqqqqqqqqqq>qqqqqqqqqqwq> ) qq>
mq> ,val2 qqwqqqqq>qqqqu
mq> ,val3 qj
Specifies associated threshold values for each storage area with
uniform format that is specified in the map-within-clause. By
setting threshold values, you can make sure that Oracle Rdb does not
overlook a page with sufficient space to store compressed data.
The threshold values specify when the page is marked as FULL
in the SPAM page free space inventory lists. For example,
if you set default values of 70, 85, and 95 percent, ranges
of guaranteed free space on each data page are 30, 15, and 5
percent, respectively. If you do not set default values, the
values are (0,0,0). With values of (0,0,0), Oracle Rdb will use the
record length when setting the SPAM fullness. Oracle Rdb will never
store a record on a page at threshold 3. The value you set for
the highest threshold can be used to reserve space on the page
for future record growth.
If you specify a value of 40 for the "val1" parameter, but do not
specify values for the "val2" or "val3" parameters, the threshold
values will be set at (40,100,100).
If you use data compression, you should use logical area
thresholds to obtain optimum storage performance.
2 – USING field-name
The names of the fields whose values will be used as limits for
partitioning the relation across multiple storage areas. Oracle Rdb
compares values in the fields to the values in the WITH LIMIT OF
clause to determine where to initially store the record.
3 – default-threshold-clause
(B)0[mdefault-threshold-clause =
qq> [4mDEFAULT[m [4mTHRESHOLDS[m ARE qqk
lqqqqqqqqqqqqq<qqqqqqqqqqqqqj
mq> ( qq> val1 qwqqqqqqqqqqq>qqqqqqqqqqwq> ) qq>
mq> ,val2 qqwqqqqq>qqqqu
mq> ,val3 qj
Specifies associated threshold values for each storage area with
uniform format that is NOT specified in the map-within-clause. By
setting threshold values, you can make sure that Oracle Rdb does not
overlook a page with sufficient space to store compressed data.
The threshold values specify when the page is marked as FULL
in the SPAM page free space inventory lists. For example,
if you set default values of 70, 85, and 95 percent, ranges
of guaranteed free space on each data page are 30, 15, and 5
percent, respectively. If you do not set default values, the
values are (0,0,0). With values of (0,0,0), Oracle Rdb will use the
record length when setting the SPAM fullness. Oracle Rdb will never
store a record on a page at threshold 3. The value you set for
the highest threshold can be used to reserve space on the page
for future record growth.
If you specify a value of 40 for the "val1" parameter, but do not
specify values for the "val2" or "val3" parameters, the threshold
values will be set at (40,100,100).
If you use data compression, you should use logical area
thresholds to obtain optimum storage performance.