Data warehouses workloads can include reading millions of rows and scans of all the
data in a table. For this type of activity, using bigger database blocks enables each block
read to deliver more data to the requesting user. To support these types of operations
best, data warehouses usually have larger blocks, such as 8 KB or 16 KB. Each I/O
operation might take a little longer due to the larger block size, but the reduced number
of operations will end up improving overall performance.
42 | Chapter 2: Oracle Architecture
When Oracle updates data, it first attempts to update the data in the same data
block. If there is not enough room in the data block for the new information, Oracle
will write the data to a new data block that could be in a different extent.
For more information on segments and extents and how they affect performance,
refer to the section on ???Fragmentation and Reorganization??? in Chapter 5. This discussion
is especially important if you are running an older release of Oracle. Oracle
Database 10g added a Segment Advisor that greatly simplifies reclaiming unused
space in current database versions.
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