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Updating indexes for block model space

The database requests data in multiples of data blocks, not operating system blocks.

If so, then the database places the block at the beginning of the free list. In this way, multiple sessions performing DML on a table can use different lists, which can reduce contention.Locally managed tablespaces, which are the default, avoid this performance problem.is the minimum unit of data that the operating system can read or write.Within a locally managed tablespace, the database can manage segments automatically or manually.For example, segments in tablespace statement, then you cannot insert rows into a block in the segment until less than 40% of the block space is used.This chapter contains the following sections: Oracle Database allocates logical space for all data in the database.The logical units of database space allocation are data blocks, extents, segments, and tablespaces.Oracle Database updates tables in the data dictionary whenever an extent is allocated or freed for reuse.For example, when a table needs an extent, the database queries the data dictionary tables, and searches for free extents.The SQL that the database executes in the background to obtain space for database objects is .Frequent use of recursive SQL can have a negative impact on performance because updates to the data dictionary must be serialized.

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