iX V6.5 (30391-90011)

Chapter 4 99

Using the Database

Opening the Database

• Access Mode 7. The database is opened for exclusive read access. No other users can

access the database concurrently. Access mode 7 operates the same as access mode 3,

except that the DBUPDATE, DBPUT, and DBDELETE procedures, which alter the

database, are disabled for the access mode 7 user.

• Access Mode 8. The database is opened for shared read access. Concurrent users must

either be in access mode 6 or 8, or using the TurboIMAGE/XL utility, DBSTORE.

TurboIMAGE/XL procedures that alter the database are not permitted. Because access

mode 8 allows only concurrent readers, a user program with this access mode can be

assured that the database values it reads are unchanging.

Selecting a Database Access Mode

When deciding which access mode to use, the following are two important considerations:

• Use the minimum capability required to accomplish the task. For example, select a

read-only access mode (5, 6, 7, or 8) if the program does not alter the database in any

way. Read access modes allow concurrent database STORE operations and do not set the

MPE/iX "ﬁle modiﬁed" ﬂag.

• Allow concurrent users to have as much capability as is required for successful

completion of the task. If the task is merely browsing through the database, producing a

quick report, or accessing an unchanging portion of the database, choose an access mode

that allows concurrent users to make database modiﬁcations to other parts of the

database. Allowing concurrent read-only access (modes 2, 4, and 8) can be appropriate

in many situations. For programs that must be assured of no concurrent structural

changes, but can tolerate simultaneous updates to entries, mode 2 is suitable. Locking

can be used to control simultaneous updates to a data entry. If it is necessary to make

additions or deletions to a database from concurrent multiple processes, modes 1 and 5

must be used. Fully exclusive operation (modes 3 and 7) are available if needed.

The following access mode selection guidelines are organized according to the task to be

performed. For some tasks, one of several modes can be selected depending on the

concurrent activity allowed with each mode.

• Programs that perform operations, which include adding and deleting entries or which

need to update detail data set search and sort items via the critical item update

(CIUPDATE) option, should open with mode 1, 3, or 4. Consider the following when

choosing among access modes 1, 3, and 4:

Access Mode 1 Can be used if other processes need to add and delete entries

simultaneously. In this case, the affected parts of the database must be

locked while performing updates, additions, or deletions.

Access Mode 3 Can be used if the program must have exclusive access to the database.

Access Mode 4 Can be used if exclusive ability to change the database is required but

access mode 6 processes need to be able to read the database while

changes are being made.

• Programs that locate, read, and replace data in existing entries but do not need to add

or delete any entries, and do not want any other processes to do so, should open the

database in access mode 2. Consider the following when choosing access mode 2: