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Teradata Database Administration – Teradata Internals by Tom Coffing, Todd Wilson

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Chapter 10 - Teradata Writes and Blocks

“Either write something worth reading or do something worth writing.”

- Benjamin Franklin

 

A Teradata Write

  • For SQL writes, Teradata uses Write Ahead Logic (WAL) to manage disk write operations.
  • Read the Data Block (if not in memory use Master Index > Cylinder Index > Data Block).
  • Place before-image of row into the Transient Journal buffer and write to the WAL log on disk.
  • Data blocks are always updated in Memory, but not always written to disk immediately.
  • The row's after-image (REDO row) is written to the WAL log on disk.
  • WAL will often batch up modifications from multiple transactions and write with a single I/O.
  • All updated data blocks in memory will be eventually aged out and written to disk. ...

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