Oracle9i SQL Reference Release 2 (9.2) Part Number A96540-02 |
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The physical_attributes_clause
lets you specify the value of the PCTFREE
, PCTUSED
, INITRANS
, and MAXTRANS
parameters and the storage characteristics of a table, cluster, index, or materialized view.
You can specify the physical_attributes_clause
in the following statements:
CREATE
CLUSTER
and ALTER
CLUSTER
: to set or change the physical attributes of the cluster and all tables in the cluster (see CREATE CLUSTER and ALTER CLUSTER).CREATE
TABLE
: to set the physical attributes of the table, a table partition, the OIDINDEX
of an object table, or the overflow segment of an index-organized table (see CREATE TABLE).ALTER
TABLE
: to change the physical attributes of the table, the default physical attributes of future table partitions, or the physical attributes of existing table partitions (see ALTER TABLE).
CREATE
INDEX
: to set the physical attributes of an index, or index partition (see CREATE INDEX).ALTER
INDEX
: to change the physical attributes of the index, the default physical attributes of future partitions, or the physical attributes of existing index partitions (see ALTER INDEX).CREATE
MATERIALIZED
VIEW
: to set the physical attributes of the materialized view, one of its partitions, or the index Oracle generates to maintain the materialized view (see CREATE MATERIALIZED VIEW).ALTER
MATERIALIZED
VIEW
: to change the physical attributes of the materialized view, the default physical attributes of future partitions, the physical attributes of an existing partition, or the index Oracle creates to maintain the materialized view (see ALTER MATERIALIZED VIEW).CREATE
MATERIALIZED
VIEW
LOG
and ALTER
MATERIALIZED
VIEW
LOG
: to set or change the physical attributes of the materialized view log (see CREATE MATERIALIZED VIEW LOG and ALTER MATERIALIZED VIEW LOG).physical_attributes_clause::=
This section describes the parameters of the physical_attributes_clause
. For additional information, refer to the SQL statement in which you set or reset these parameters for a particular database object.
Specify a whole number representing the percentage of space in each data block of the database object reserved for future updates to the object's rows. The value of PCTFREE
must be a value from 0 to 99. A value of 0 means that the entire block can be filled by inserts of new rows. The default value is 10. This value reserves 10% of each block for updates to existing rows and allows inserts of new rows to fill a maximum of 90% of each block.
PCTFREE
has the same function in the statements that create and alter tables, partitions, clusters, indexes, materialized views, and materialized view logs. The combination of PCTFREE
and PCTUSED
determines whether new rows will be inserted into existing data blocks or into new blocks.
When altering an index, you can specify this parameter only in the modify_index_default_attrs
clause and the split_partition_clause
.
Specify a whole number representing the minimum percentage of used space that Oracle maintains for each data block of the database object. A block becomes a candidate for row insertion when its used space falls below PCTUSED
. PCTUSED
is specified as a positive integer from 0 to 99 and defaults to 40.
PCTUSED
has the same function in the statements that create and alter tables, partitions, clusters, materialized views, and materialized view logs.
PCTUSED
is not a valid table storage characteristic for an index-organized table (ORGANIZATION
INDEX
).
The sum of PCTFREE
and PCTUSED
must be equal to or less than 100. You can use PCTFREE
and PCTUSED
together to utilize space within a table more efficiently.
You cannot specify this parameter for an index or for the index segment of an index-organized table.
See Also:
Oracle9i Database Performance Tuning Guide and Reference for information on the performance effects of different values |
Specify the initial number of concurrent transaction entries allocated within each data block allocated to the database object. This value can range from 1 to 255 and defaults to 1, with the following exceptions:
INITRANS
value for a cluster or index is 2 or the default INITRANS
value of the cluster's tablespace, whichever is greater.In general, you should not change the INITRANS
value from its default.
Each transaction that updates a block requires a transaction entry in the block. The size of a transaction entry depends on your operating system.
This parameter ensures that a minimum number of concurrent transactions can update the block and helps avoid the overhead of dynamically allocating a transaction entry.
The INITRANS
parameter serves the same purpose in the statements that create and alter tables, partitions, clusters, indexes, materialized views, and materialized view logs.
Specify the maximum number of concurrent transactions that can update a data block allocated to the database object. This limit does not apply to queries. This value can range from 1 to 255 and the default is a function of the data block size. You should not change the MAXTRANS
value from its default.
If the number of concurrent transactions updating a block exceeds the INITRANS
value, then Oracle dynamically allocates transaction entries in the block until either the MAXTRANS
value is exceeded or the block has no more free space.
The MAXTRANS
parameter serves the same purpose in the PARTITION
description, clusters, materialized views, and materialized view logs as in tables.
The storage_clause
lets you specify storage characteristics for the table, object table OID index, partition, LOB data segment, LOB index segment, or index-organized table overflow data segment. This clause has performance ramifications for large tables. Storage should be allocated to minimize dynamic allocation of additional space.