TS/MP Pathsend and Server Programming Manual (G06.24+, H06.03+)

Writing Pathway Servers

NonStop TS/MP Pathsend and Server Programming Manual–132500

4-8

Locking Records

If your application uses the TMF subsystem, your servers must follow the TMF locking

rules. Locking gives the TMF subsystem the control required to ensure that transactions

are presented with a consistent view of the database. With respect to the locking of

records, you must consider the following aspects of your application:

•

Repeatable reads.

•

Errors that result from locks being held by the transaction identifier instead of the

process identifier and OPENID of the file opener.

•

Errors that result from reading deleted records.

•

Batch updates by a transaction that acquires a large number of locks. You should use

file locks instead of record locks for batch updating.

For details about how to handle these aspects of your application, refer to the

NonStop TM/MP Application Programmer’s Guide.

Grouping Transaction Operations

Your application can view the transaction as a logical unit of work; for example, the

order header and all of the detail items in a purchase order might be such a work unit.

The TMF subsystem, however, treats the transaction as a physical unit of recovery.

When you use the TMF subsystem in your application, you must consider this

difference.

Basically, you need to answer certain questions. What is the logical unit of work that

you want to accomplish within an application? How can the work be divided into a

number of transactions that can be recovered by the TMF subsystem?

Factors that influence the answers to these questions are:

•

Concurrency: How long will record locks be held by a transaction?

•

Performance: How much server activity and how many display screens are involved

in the choice of one conversion strategy over another?

•

Consistency: Are the units of recovery large enough to ensure that your criteria for

consistency will be maintained?

In view of these factors, two guidelines can help you decide how to group the database

accesses made by an application into a single transaction:

•

Any group of accesses that together modify the database from one consistent state to

another consistent state should be a single TMF transaction.

•

Any group of accesses that require a consistent view of the database should be a

single TMF transaction.

The following examples demonstrate how you might apply these guidelines.