PCTFREE parameter when you create the table and PCTUSED What does it mean?

Jan 7 posted in Oracle (RSS), 155 views.

pctfree: used to specify the BLOCK in the smallest space necessary to retain the ratio.
pctused: as a percentage of value, when the BLOCK has been used in the space reduced to the values below, the BLOCK is available to reach or exceed the value of the BLOCK is not useful.
Generally independent segment in the control structure of an object, use these two parameters to control the BLOCK of storage management.
initrans: the specified operation can be complicated by the number of the affairs of the table.

With the CREATE command PCTUSED, PCTFREE, INITTRANS, MAXTRANS, FREELIST GROUPS and FREELISTS parameters to control the table, index or cluster of data block space usage.

Can use PCTFREE and PCTUSED parameter control data block when entering or leaving the table, index or cluster of available inventory. PCTFREE parameter used to set the maximum threshold to control the line of the future operation of the preservation of the update data block space. When a data block so that when PCTFREE full, ORACLE is available from the corresponding section of the list to remove the block. If you have only a few of the update operation is expected to increase the size of the line, you can set a lower PCTFREE value (such as 5 or 10), making ORACLE fill more space for each block. However, if you expect the update operation will always increase the size of the line, it will PCTFREE is set to a higher value (such as 20 or 30), making ORACLE update operation for the existing row of blocks to reserve more space; Otherwise, it will that existing chains.

PCTUSED parameter can be used to set thresholds for most small to control when a data block should be put back to the corresponding segment available list. For example, all segments PCTUSED default setting is 40%, Therefore, when the transaction processing to delete data blocks in the row, if it is only 39% are filled, ORACLE data blocks back into the appropriate section of the list of available . If you expect little delete operation, you can set the PCTUSED to a higher value (eg 60), when the accidental deletion occurs, the data block pop-up list is available. However, if you are expected to be PCTUSED set to a lower value (eg 40), so that ORACLE not often produce blocks of available space in the table moved into or out of overhead.

Can use the INITRANS Parameter Optimization and MAXTRANS how ORACLE tables, data cluster or index data blocks allocated transaction entries. INITRANS parameter for the transaction processing options to determine the number of data blocks pre-allocated space for the head. When you have many concurrent transactions are expected to be involved in a block, it can deal with matters related to items for the pre-allocate more space to avoid the overhead of dynamic allocation of the space. MAXTRANS parameter limits the use of a data block in parallel transaction amount. When you are dealing with a number of issues are expected to be parallel access to a small table, then when you create a table, the table should be set pre-transaction items to allocate more blocks of space, high MAXTRANS parameter values to allow a number of issues dealing with concurrent access to The table INITRANS and MAXTRANS the corresponding parameter settings may be somewhat lower (eg, respectively, 2 and 5). Using this setting, rarely transaction reservation cellar, so that the table data block more space for data.

Can use the STORAGE clause FREELIST GROUPS parameter control section of the list of groups the amount of data available. FREELISTS parameter settings using the available list of the number of each group.