Availability and Optimization of Free Space in a Data Block(五)

Two types of statements can increase the free space of one or more data blocks:

DELETE statements, and UPDATE statements that update existing values to smaller

values.

The released space from these types of statements is available for subsequent

INSERT statements under the following conditions:

■ If the INSERT statement is in the same transaction and subsequent to the

statement that frees space, then the INSERT statement can use the space made

available.

■ If the INSERT statement is in a separate transaction from the statement that frees

space (perhaps being run by another user), then the INSERT statement can use the

space made available only after the other transaction commits and only if the space is needed.

Released space may or may not be contiguous with the main area of free space in a

data block. Oracle coalesces the free space of a data block only when (1) an INSERT or UPDATE statement attempts to use a block that contains enough free space to contain a new row piece, and (2) the free space is fragmented so the row piece cannot be

inserted in a contiguous section of the block.

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