Oracle Wait Interface: A Practical Guide to Performance Diagnostics & Tuning

Sampling for Performance Data with SQL-less SGA Access

The critics of the SQL or PL/SQL sampling method contend that the sampling interval is too coarse and that there is a low limit on the number of times a program can sample data through views every second. There is a way to sample Oracle performance data at a high frequency without using SQL in Unix-like systems. This method is known as SGA Direct Access. It uses an external program, typically written in the C language, to obtain Oracle data by reading the SGA shared memory segment directly. This method is a little more complex than the rest of the monitoring methods, but it has advantages over them. Because this is an uncommon method, we provide the details in Appendix D.