Chapter 9. Understanding the OnLine Utilities

The discussion of the Informix utilities will be split over this and the next chapter. The IDS engine, while an order of magnitude more capabable than the earlier OnLine engines, still stems from an OnLine code base. Since the IDS engine was to be backwardly compatible to the earlier OnLine engines, much remained the same from OnLine to IDS. In fact, for the most part, the OnLine utilities are a subset of the same utilities for IDS. Since IDS does more, its utilities are more extensive, but just about everything that works in OnLine works the same, to a certain extent, in IDS.

This entire chapter is mostly unchanged from the first edition of the book. This chapter applies specifically to the OnLine engines. We will duplicate much of this chapter in the next chapter on IDS utilities, but there are enough differences between the two that it will be less confusing if we consider them separately. Chapter 10 will specifically cover the onstat utility in IDS.

The tb/onstat utility is the most important of the entire suite of OnLine utilities. It is used to inspect the pseudotables that are held in shared memory structures. In OnLine systems, this information cannot be determined without using the tb/onstat utility. Beginning with OnLine 6.0, Informix included the SMI (System Monitoring Interface) tables, which provide much of the same information as provided in tb/onstat in pseudotable form that is accessible by SQL statements. The SMI tables will be discussed in detail in Chapter 11.

Why is this information important? The main reason is that this is where the operations of the OnLine "black box" are recorded and controlled. For a regular user, the engine is simply the mechanism that translates his SQL statements into actual data returned from the database. This level of detail is enough for most users. The database administrator needs much more detailed information to troubleshoot problems, improve performance, and generally know what is going on inside the engine itself. For the same reasons that it is important for the DBA to understand the architecture and internal operations of the engine, the database administrator needs to understand all of the options, output codes, and interrelations of the tbstat program. The tbstat program is well documented in the Informix OnLine Administrator's Guide, and the reader is urged to become familiar with the relevant sections of the Guide. What the Guide doesn't cover, however, is the "why" and "how does this relate to my problem" type of question. The guide's information needs to be assimilated and used, but in order for the DBA to use the tool effectively, the administrator needs to know how the pieces fit together.