How to Read This Chapter

This chapter will discuss the internal architecture of the earlier OnLine 5.XX engines and more advanced architecture of Informix Dynamic Server 7.XX. When the first edition of the book was released, it contained specifics only on the OnLine 5.XX engines. This revision will cover the Informix Dynamic Server 7.XX (IDS) engines as well.

Both engine versions have a lot in common. The major area of differences lies in the multithreaded architecture of IDS as opposed to the two-process architecture of OnLine. Areas such as shared memory and disk structures also differ, but not as drastically as the underlying architecture.

The task of discussing both engines together in somewhat complicated by the differences in naming the utilities. Most of the OnLine utilities began with the prefix "tb," as in tbstat, tblog, and tbmonitor. In IDS, the "tb" was replaced by "on," as in onstat, onlog, and onmonitor. When we are discussing areas where the two engines do not differ significantly, we will refer to the utilities with a "tb/on" prefix, as in tb/onlog, tb/onstat, and tb/onmonitor. In these cases, you should use either "tb" or "on" as a prefix for your actual commands, depending upon your versions. Many UNIX IDS systems include a link from the old name to the new name, and you can enter either the old or new name Scripts included with book will continue to have the "tb" prefix, and a separate series of scripts will be available with the "on" prefixes for IDS systems.

In some cases, the "tb" and "on" programs have different options that are unique to either OnLine or IDS. An example would the onstat -g commands in IDS systems. There is no corresponding tbstat -g command since the -g option is recognized only in IDS. In these cases, we will use the "on" prefixes only.

When I refer to "Informix," "Informix engines" or "Informix products," I'm generalizing across both the OnLine and IDS products. When I'm addressing something that differs between the products, I'll talk about either "OnLine" or "IDS."

We'll also take a UNIX-centric view of the universe and assume that the engines are running on UNIX. Remember that the IDS products also run on Windows NT. There'll be a chapter that later specifically addresses NT, but all of the UNIX concepts are applicable to NT as well.