Technical data

Snapshot tracing is most useful when you can accurately anticipate when the

events you want to trace are going to occur; otherwise, the trace information you

require may not have been generated when you collect the contents of the buffer,

or it may have been overwritten by more recent trace information. Note also that

snapshot tracing is less useful when tracing remote tracepoints, since the buffer

in this case is on the remote server and holds less trace information than the

buffer on the local VMS system.

2.2.4 Restrictions on Tracing

You can perform live, detached, or snapshot tracing on both local and remote

tracepoints. However, you should note the following restrictions:

• You can perform only one type of tracing within a single invocation of CTF;

that is, you cannot mix detached, live, and snapshot tracing within the same

invocation of CTF.

• You cannot perform both local and remote tracing within the same invocation

of CTF.

• Only one system can be traced within a single invocation of CTF. This means

that if you are performing remote tracing, all the remote tracepoints traced

within that invocation of CTF must be on the same server.

• Only one invocation of CTF can trace local tracepoints at any given time.

This means that you cannot, for example, invoke CTF, start detached tracing

on a local tracepoint, exit from CTF, then re-invoke CTF to start detached

tracing on some other local tracepoint.

2.3 CTF Structure

This section describes the components of CTF that perform the functions

described in Section 2.2.

CTF has two major components:

• A VMS utility that is invoked by the DCL command TRACE. This utility

supports the CTF command interface, which allows you to:

Start and stop collection of trace records from speciﬁed tracepoints

Analyze and display the trace records stored in a trace ﬁle

Alter the format in which trace records are displayed

Assign CTF command strings to particular keys

• CTF support. There is a CTF support component in each local VMS system

and remote server that supports CTF. CTF support:

Starts and stops collection of trace records from selected tracepoints (in

response to CTF commands)

Passes trace records from the networking software that generates them to

the TRACE utility

CTF support functions are implemented differently on VMS systems and remote

servers. Figure 2–2 shows how live tracing is supported on local VMS systems

and remote servers. Figure 2–3 shows how detached tracing is supported on local

VMS systems and remote servers.

2–4 Technical Overview