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Lesson 1

Using Oracle Blocks efficiently

This module will discuss the issues surrounding the interaction between Oracle data blocks and the database engine. As we know,
  1. the size of the data blocks,
  2. the structure of the rows on the data blocks and
  3. the settings of the table storage parameters
all have an effect upon the contents of the data block and the performance of our database.
By the time you finish this module, you should be able to:
  1. Determine the appropriate db_block_size
  2. Optimize space usage within blocks
  3. Describe internals of the segment header
  4. Set proper values for PCTUSED and PCTFREE
  5. Describe the effect of the high water mark on full-table scans
  6. Detect and resolve row migration

One of the most confusing issues surrounding storage space in an Oracle database is setting the proper data block size. Decide on the best default database block size. The default block size defined by DB_BLOCK_SIZE cannot be changed later without reinstalling the database. Note that Oracle can support multiple block sizes within a single database.
The default size for the database blocks is set via the DB_BLOCK_SIZE parameter specified in the parameter file during database creation. Managing the size of the database buffer cache is an important part of managing and tuning the database.
The next lesson reviews the db_block_size parameter setting.