iX V6.5 (30391-90011)

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