16.10 - Teradata Database File System Startup - Teradata Database

Teradata Database Support Utilities

Teradata Database
June 2017
File system startup is part of the normal sequence of events that are part of Teradata Database system startup sequence:
  1. File system startup
  2. Start the AMPs
  3. Start the PEs
  4. Voting for Transaction Recovery
  5. Transaction Rollback

A normal startup of the Teradata Database file system starts the WAL log prior to starting the normal file system. The key phases of Teradata file system startup include the following:

  • Read the snapshot MI from disk and examine it for structural consistency.

    If it is consistent, it can be used, avoiding the necessity of reading CIs and constructing the MI, which takes longer.

  • Build the WAL Master Index (WMI).

    This is the index structure for the WAL log. The WAL log contains the Redo records and the Transient Journal (TJ) records.

  • Perform Redo analysis and replay.

    This scans the WAL log for Redo records and analyzes which records should be applied, and replays the necessary modifications, to bring the CI structures up-to-date.

    Because the WAL protocol allows for the delayed writing of modified blocks to their home disk addresses, the blocks on disk are only completely valid after the Redo processing is complete. When the processing is finished, the CIs have been updated to reflect any cylinder migrates or other modifications that were performed.

    If the MI snapshot read from disk was valid, redo processing updates the MI.

  • If the snapshot or in-memory MI was inconsistent or corrupt, REDO processing ignores the MI and the system rebuilds the MI from an inspection of CIs on the AMP.

The specific File System startup sequence on each AMP is as follows:

  1. Get the list of cylinders for this AMP from Teradata Virtual Storage (VS).
  2. Validate Segment Zero (SEG0), the File Information Block (FIB), and MI.
  3. Get the FSYS Trace segment.
  4. Process the DEPOT blocks.
  5. Process the WAL log:
    1. Build the WMI.
    2. Perform Redo analysis.
    3. Perform Redo replay.
  6. Start the File System.
    1. Clean up cylinder index descriptors (CIDs) with special flags.
    2. Rebuild the free sector list.
    3. Clean up pending migrate flags.
    4. Validate cylinders in FSYS structures against Teradata VS list.
  7. Start File System background tasks.

When a system is corrupted, some or all of the above steps may be difficult to complete. The Filer diagnostic options allow trained personnel to start Filer even when errors are encountered during file system startup. The options also provide the ability to control which phases of the file system startup sequence are executed. This allows users to skip the startup phases which have errors and to use Filer to troubleshoot and repair the problems.

Errors encountered during WAL log startup or during Redo processing will generally abort the startup. You can use the Filer diagnostic options to analyze the problems and possibly recover from the errors.