Oracle Storage Parameter __oracle

Turn from: http://hi.baidu.com/hanbingxiaoshi/blog/item/1cbfc2f25d126418b17ec568.html

Available for: Table spaces, rollback segments, tables, indexes, partitions, snapshots, snapshot logs

Parameter name	Default value	Minimum value	Maximum Value	Description
INITIAL	5 (Data block)	2 (data block)	Operating system limits	The size, in bytes, of the first extent assigned to segment, which cannot be changed in the ALTER statement, created by the minimum value if the specified value is less than the minimum value.
NEXT	5 (Data block)	1 (data block)	Operating system limits	The second extent is equal to the initial value of Next, next value = The previous next size multiplied by (1+pctincrease/100), and the minimum value is created if the specified value is less than the minimum value. If you change the value of next in the ALTER statement, the next assigned extent will have the specified size, regardless of the extent size and pctincrease parameter values of the last assignment.
Minextents	1 (Extent) Rollback segment is 2 extent	1 (Extent) Rollback segment is 2 extent	Operating system limits	Number of extent allocated when segment first created
Maxextents	Depending on the size of the data block	1 (Extent) Rollback segment is 2 extent	Unlimited	As the amount of data in the segment grows, the maximum number of extent that can be allocated
Pctincrease	50% (0% in Oracle816)	0%	Operating system limits	Specifies the percentage increase in the third and subsequent extent relative to the previous extent, If Pctincrease is 0, all newly added extent in segment are the same size, equal to the value of next. If the pctincrease is greater than 0, the next value is computed each time (with the formula above), Pctincrease cannot be a negative number. When you create a rollback segment, you cannot specify this parameter, which is fixed to 0 in the rollback segment.
OPTIMAL	----	cannot be smaller than the rollback segment initial allocation space	Operating system limits	In relation to the rollback segment only, when the rollback segment exceeds the set range of this parameter because of the growth and expansion, the Oracle system dynamically allocates the extents according to the situation, attempting to reclaim the extent of the multiple allocations.
Freelists	1	1	Data block Size limit	Freelists and freelist groups parameters can only be specified in Create TABLE, CLUSTER, index. Number of free lists in each free list group in a pattern object
Freelist GROUPS	1	1	Depending on the number of Oracle parallel instances	The number of free list groups of database objects created by the user, using this parameter only when using the OPS parallel server option, and one instance for a group.
Buffer_pool	----	----	----	Defines a default buffer pool (cache) for a schema object, all blocks of which are stored in the specified cache, and are not valid for tablespaces or rollback segments.

The 
 recommends that the Pctincrease parameter be set to 0 to minimize fragmentation so that each extent is the same (equal to the next value) once an object is established, its initial and minextents parameters cannot be modified (Oracle Modifiable minextents parameter in 816) any modification to next and pctincrease only affects those that were later allocated extent when assigning a new extent, the system assigns a extent directly to the next value and then uses the formula: previous Next value * 
　　
　　(1+pctincrease/100) Calculates the size of the next extent that should be allocated, and saves the results to the Next_extent column of the relevant data dictionary as the next extent size to be allocated.
　　CREATE TABLE Test (a number) STORAGE (INITIAL 100K NEXT 100K minextents 2 maxextents pctincrease 100); Explanation: Initially assign two extent to the test table, the first extent is 100K, the second extent is 100K because of next=100k, and if the data in the table is increased, a third extent should be allocated because PCTI 
　　Ncrease is 100, then the third extent is 200k=100k+100k; The fourth extent is 400k=200k+200k. You can view parameter settings through the data dictionary table dba_tables, All_tables, User_tables, for example: select Table_name,initial_extent,next_extent, Min_extents,ma
　　X_extents,pct_increase from User_tables; table_name initial_extent next_extent min_extents max_extents pct_increase----------------------------------------- ----------------------------TEST 106496 212992 2