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Oracle interaction with the UNIX disk I/O sub-system

We have already covered the use of STATSPACK and the UNIX iostat utility to see disk reads and writes from Oracle, but we are now ready to take a closer look at the interaction between Oracle and the UNIX disk sub-system.

Remember, the tools we presented in Chapter 4 give us techniques for monitoring disk I/O over time periods, but we still need details about I/O waits and other internal UNIX events that are associated with disk I/O.

Once a background process issues an I/O request, it manifests itself in UNIX as an I/O object. To UNIX, an I/O object represents a byte stream and UNIX is not aware that it is reading a database file. Within UNIX, various operations are defined on the byte stream:

read()- Read to the UNIX stream
write()- Write to the UNIX stream
close() – Close the UNIX stream

While these I/O details are well hidden inside the bowels of Oracle, there are some techniques that we can use to see I/O details.

The above is an excerpt from the "Oracle UNIX Administration Handbook" by Oracle press, authored by Donald K. Burleson.

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