TurboIMAGE/XL Database Management System Reference Manual (30391-90012)

100 Chapter4
Using the Database
Opening the Database
Access Mode 2 Can be used if processes are allowed to update the database
concurrently. Locking should be used to coordinate updates. The critical
item update (CIUPDATE) option, which can permit you to update the
values of detail data set search and sort items, is not available in this
mode.
• Programs that only locate and read or report on information in the database should
open with one of the read-only access modes. In this case, the access mode selected
depends upon either the type of process running concurrently or the need for an
unchanging database while the program is running. Consider the following when
choosing among access modes 5, 6, 7, and 8:
Access Mode 5 Can be used if concurrent processes will operate in access mode 1 or 5.
Parts or all of the database should be locked to prevent concurrent
changes during one or more read operations. Because concurrent access
mode 1 processes are allowed, programs performing chained reads
should lock the chain (see the discussion of DBGET in chapter 5).
Access Mode 6 Can be used if it is not important what other processes are doing to the
database. In this case, access mode 2 processes can update entries; one
access mode 4 user can update, add, or delete entries; or access mode 6
or 8 users can read entries while the program is using the database.
Access Mode 7 Can be used if the program must have exclusive read access to the
database.
Access Mode 8 Can be used if other processes are allowed to read but not modify the
database. In this case, access mode 6 and 8 users can read entries while
the program is using the database.
Locking within a Database Process
Refer to the locking discussion later in this chapter for considerations when locking and
unlocking transactions within a database process.
User Transaction Logging
Users opening the database in access modes 1 through 4 use the MPE/iX user logging
facility if the database administrator has enabled the database for logging (a procedure
described in chapter 7). In this case, calls to the TurboIMAGE/XL intrinsics listed in Table
4-3. are automatically logged to a log file. Note that nothing is logged for programs opening
the database with read-only access modes (5 through 8), regardless if the database was
enabled for logging. The logging facility is described more fully later in this chapter and in
chapter 7.
Table 4-3. Logged Intrinsics
DBBEGIN DBCLOSE DBDELETE DBEND
DBMEMO DBOPEN DBPUT DBUPDATE
DBXBEGIN DBXEND DBXUNDO