Oracle Database - Full Table Scans

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1 - About

Data Access Path - Full Table Scan in Oracle

During a full table scan, all blocks in the table that are under the high water mark are scanned. Each row is examined to determine whether it satisfies the statement's WHERE clause.

When Oracle performs a full table scan, the blocks are read sequentially. Because the blocks are adjacent, I/O calls larger than a single block can be used to speed up the process. The size of the read calls range from one block to the number of blocks indicated by the initialization parameter DB_FILE_MULTIBLOCK_READ_COUNT. Using multiblock reads means a full table scan can be performed very efficiently. Each block is read only once.

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3 - Hint

  • FULL: Full Table Scan Hints: Use the hint FULL(table alias) to instruct the optimizer to use a full table scan.
  • CACHE/NOCACHE: You can use the CACHE and NOCACHE hints to indicate where the retrieved blocks are placed in the buffer cache. The CACHE hint instructs the optimizer to place the retrieved blocks at the most recently used end of the LRU list in the buffer cache when a full table scan is performed.
db/oracle/full_table_scans.txt · Last modified: 2017/09/13 20:33 by gerardnico