Chapter 9. GT.M Database Structure(GDS)

Revision History
Revision V6.3-008	24 April 2019	In “GDS Records ”, Update breakdown of the record header fields. In “GDS Blocks ”, Update breakdown of field within the block header.
Revision V6.3-007	04 February 2019	In “File Header Data Elements ”, Add a missing word to the Maximum Record Size description
Revision V6.3-006	26 October 2018	In “String Subscripts ”, UTF-8 tweaks
Revision V6.3-005	03 July 2018	In “Exercise 2: Rectifying a deadlock situation”, made formatting adjustments for the caution note.
Revision V6.3-001	20 March 2017	In “File Header Data Elements ”, removed references to OpenVMS and added the descriptions of WIP queue cache blocks, DB is auto-created, DB shares gvstats. LOCK crit sharing, AsyncIO
Revision V6.0-003/1	19 February 2014	In “File Header Data Elements ”, updated the descriptions for V6.0-003.
Revision V6.0-003	27 January 2014	In “GDS Blocks ”, corrected the description of block header fields.

Contents

Database File Organization with GDS

Database File Header
File Header Data Elements

Local Bitmaps

Master Bitmap

Database Structure

Tree Organization
GDS Blocks
GDS Records
GDS Keys
Compression Count
Use of Keys
Characteristics of Keys
Global Variable Names
String Subscripts
Numeric Subscripts

GDS is an FIS proprietary internal database structure used to store global variables and lock resource names. A high-level understanding of GDS can help database administrators correctly interpret GT.M logs/error messages, and maintain database metrics. You should always consult GT.M support (gtmsupport@fisglobal.com) in the unlikely event of getting database integrity issues.

	Note
	This chapter provides a high-level overview of GDS components. A comprehensive description of all the components of GDS is beyond the scope of this chapter.

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