TurboIMAGE/XL Database Management System Reference Manual (30391-90012)
Table Of Contents
- 1 Introduction
- 2 Database Structure and Protection
- 3 Defining a Database
- 4 Using the Database
- 5 TurboIMAGE/XL Library Procedures
- Using TurboIMAGE/XL Intrinsics
- DBBEGIN
- DBCLOSE
- DBCONTROL
- DBDELETE
- DBEND
- DBERROR
- DBEXPLAIN
- DBFIND
- DBGET
- DBINFO
- INTRINSIC NUMBER 402
- Syntax
- Parameters
- Discussion
- Mode 101: Item Number
- Mode 102: Item Name
- Mode 103: Items in Database
- Mode 104: Items in Data Set
- Mode 113: BTREEMODE1 and Wildcard Character
- Mode 201: Set Number
- Mode 202: Set Name
- Mode 203: Sets in Database
- Mode 204: Sets with Item
- Mode 205: Set Capacity
- Mode 206: Number of Data Set Chunks
- Mode 207: Size of Data Set Chunks
- Mode 208: Primary and Actual Capacity
- Mode 209: B-Tree Attachment
- Mode 301: Paths
- Mode 302: Key or Search Item
- Mode 401: Logging
- Mode 402: ILR
- Mode 403: Dynamic Roll-Back
- Mode 404: Logging Subsystem Information
- Mode 406: Database Information
- Mode 501: Subsystem Access
- Mode 502: Critical Item Update
- Modes 8nn: Third-Party Indexing
- Mode 901: Language
- DBLOCK
- DBMEMO
- DBOPEN
- DBPUT
- DBUNLOCK
- DBUPDATE
- DBXBEGIN
- DBXEND
- DBXUNDO
- 6 Host Language Access
- Model Program
- ORDERS Database Model Program
- Main Body of Program
- Opening the Database
- Retrieving All the Records on a Chain (with Item Level Locking)
- Retrieving a Data Entry Using a Record Number
- Retrieving Master Data Using a Key Value
- Retrieving Data Serially (with Set Level Locking)
- Adding an Entry
- Updating an Entry
- Deleting an Entry
- Rewinding a Data Set
- Obtaining Database Information
- Obtaining Error Messages and Explanations
- Closing the Database
- C
- COBOL II
- Defining Data Types, Variables, and Intrinsics
- Main Body of Program
- Opening the Database
- Retrieving All the Records on a Chain (with Item Level Locking)
- Retrieving a Data Entry Using a Record Number
- Retrieving Master Data Using a Key Value
- Retrieving Data Serially (with Set Level Locking)
- Adding an Entry
- Updating an Entry
- Deleting an Entry
- Rewinding a Data Set
- Obtaining Database Information
- Obtaining Error Messages and Explanations
- Closing the Database
- FORTRAN 77
- Pascal
- RPG
- 7 Logging and Recovery
- Database Utilities Used in Logging and Recovery
- Recovery Options
- Logical Transactions
- Dynamic Roll-Back Recovery
- Intrinsic Level Recovery
- Logging Preparation
- Step 1--Checking MPE/iX Logging Configuration
- Step 2--Acquiring Logging Capability
- Step 3--Logging to Tape or Disk
- Step 4--Building a Log File for Logging to Disk
- Step 5--Creating the Log Identifier
- Step 6--Setting the Log Identifier
- Step 7--Setting Flags for the Database Backup Copy
- Step 8--Making a Database Backup Copy
- TurboSTORE/iX 7x24 True-Online Backup
- Logging Status
- Logging Maintenance
- Roll-Forward Recovery
- Roll-Back Recovery
- DBRECOV Commands Used with Roll-Forward and Roll-Back Recovery
- Recovery Tables
- Post-Recovery Options
- The Mirror Database
- 8 Using the Database Utilities
- Restructuring the Database with TurboIMAGE/XL Utilities
- Summary of Utility Routines
- Utility Program Operation
- DBLOAD
- DBRECOV
- >CONTROL
- >EXIT
- >FILE
- >RECOVER
- >ROLLBACK
- >RUN
- DBRESTOR
- DBSTORE
- DBUNLOAD
- DBUTIL
- >>ACTIVATE
- >>ADDINDEX
- >>CREATE
- >>DEACTIVATE
- >>DETACH
- >>DISABLE
- >>DROPINDEX
- >>ENABLE
- >>ERASE
- >>EXIT
- >>HELP
- >>MOVE
- >>PURGE
- >>REBUILDINDEX
- >>REDO
- >>RELEASE
- >>SECURE
- >>SET
- >>SHOW
- Syntax
- Parameters
- Example (Show Users)
- Example Discussion
- Example (Show All)
- Example Discussion
- Example (Show Capacity)
- Format of Show Device List
- Example (Show Device)
- Format of Show Indices
- Example (Show Indices)
- Format of Show Locks List
- Example 1 (Show Locks)
- Example 1 Discussion
- Example 2 (Show Locks)
- Example 2 Discussion
- >>VERIFY
- 9 Using a Remote Database
- 10 Internal Structures and Techniques
- 11 B-Tree Indices
- A Error Messages
- B Results of Multiple Access
- C Database Design Considerations
- D Multiple Calls to DBLOCK
- E TurboIMAGE/XL Log Record Formats
- F MPE/iX Log Record Formats
- G Recovery and Logging Quick Reference
- H TurboIMAGE/XL versus TurboIMAGE/V
Chapter 4 117
Using the Database
Using the Locking Facility
Using the Locking Facility
The DBLOCK procedure applies a logical lock to a database or one or more data sets or data
entries. The DBUNLOCK procedure releases these locks.
Locking can be viewed as a means of communication and control to be used by mutually
cooperating users. The locking facility provides a method for protecting the logical
integrity of the data shared in a database. With the DBLOCK procedure, application
programs can isolate temporarily a subsection of the database in order to perform a
transaction against the isolated data. Locking is not required to protect the structure of
the database. TurboIMAGE/XL has internal mechanisms that do this.
If a program opens the database in access mode 1 and locks a part of the database, it can
perform the transaction with the certain knowledge that no other user will modify the data
until the application program issues a DBUNLOCK call. This is because TurboIMAGE/XL
does not allow changes in access mode 1 unless a lock covers the data to be changed. If one
process has the database opened in access mode 1, TurboIMAGE/XL requires that all other
processes that modify the database must also operate in access mode 1.
The DBLOCK procedure operates in one of six modes. Modes 1 and 2 can be used for locking
the database and modes 3 and 4 for locking a data set. In modes 5 and 6, you describe the
database entity or entities to be locked using lock descriptors.
At the data entry level, locking is performed on the basis of data item values. For example,
suppose a customer requests a change in an order the customer has placed. The data
entries for the customer's account that are in the SALES data set could be locked while the
order is changed and other database activity can continue concurrently.
Lock Descriptors
A lock descriptor is used to specify a group of data entries that are to be locked. It consists
of a data set name or number, a data item name or number, a relational operator, and an
associated value. For purposes of this discussion, the notation dset : ditem relop value is
used. For example, the lock descriptor SALES:ACCOUNT = 89393899 requests locking of all
the data entries in the SALES data set with an ACCOUNT data item equal to 89393899.
Note that the result of specifying a single lock descriptor can be that none, one, or many
entries are locked depending on how many entries qualify.
The following relational operators can be used:
• less than or equal (<=)
• greater than or equal (>=)
• equal (= or =), where indicates a space character
The value must be specified exactly as it is stored in the database. A lock will succeed even
if no data item with the specified value exists in the data set; no check is made during the
DBLOCK procedure to determine the existence of a particular data item value. This allows
you to use techniques such as issuing a lock to cover a data entry before you actually add it
to a data set.