16.10 - SNAPMI - Teradata Database

Teradata Database Support Utilities
prodname
Teradata Database
vrm_release
16.10
created_date
June 2017
category
Configuration
featnum
B035-1180-161K

Purpose

Selects and displays the snapshot MI. Displays information about where the MI is stored on disk. Provides an option to invalidate the snapshot MI, forcing the MI to be rebuilt from CIs at the next file system startup.

Syntax

The online help lists the display options (/P, /S, /M, /L, /H, /V, /X) as /dispopt.


/P
Positions to the snapshot MI in memory. Nothing is displayed unless a problem exists.
/S
Shows the fixed area and a formatted display of the first and last CID of the snapshot MI segment.
When used with the CYLINFO option, displays only the snapshot MI CIDs.
/M
Shows the fixed area and a formatted display of all the CIDs in the snapshot MI segment.
When used with the CYLINFO option, displays snapshot MI CIDs and the start sector of each snapshot MI chunk. Periodically, the snapshot MI in memory is divided into chunks that are individually written to disk.
/L
Shows the fixed area and a formatted display of all the CIDs in the snapshot MI segment.
When used with the CYLINFO option, displays all snapshot MI chunk headers.
/H
Displays a hex dump of the snapshot MI segment.
/V
Verifies that the snapshot MI segment has all CIDs in the correct order, that all sectors are accounted for, and matches the setting of the FIB.
/X
Same as /L.
CYLINFO
Displays the disk location of the snapshot MI.
INVALIDATE
Invalidates the snapshot MI, forcing the system to rebuild the MI at the next file system startup by reading the CIs.

Usage Notes

The prompt for the snapshot MI selector is shown below:

SNAPMI ==>

In addition to global and upper-level commands, the following lower-level commands are allowed at the SNAPMI prompt:

  • DISPLAY (without an ordinalrange)
  • DROP
  • PATCH

When the snapshot MI is written to disk, it is divided into chunks, and each chunk is written individually. If checksums are enabled, each chunk includes a checksum. The checksum value for the chunk is stored within the chunk header data. When the snapshot MI is restored during system startup, these checksums are verified to ensure the integrity of the snapshot MI. CIDs with checksums will show additional checksum columns in the SNAPMI output screen.