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Oracle Performance Tuning and Optimization
Minimizing Free List ContentionOne other area of possible contention is in the free list. The free list is maintained to provide a faster mechanism to get free data blocks from the buffer cache. The free list contains a linked list of blocks in the segment that has space available. Contention on the free list can be determined by looking at the dynamic performance table, V$WAITSTAT. Use the following SQL statement to obtain this information: SQL> SELECT class, count 2 FROM v$waitstat 3 WHERE class = 'free list' CLASS COUNT ------------------ -------- free list 0 If the free list number is greater than 1 percent of the total number of requests, you should add more free lists. Remember that the total number of requests is determined from the sum of database block gets and consistent gets from V$SYSSTAT as shown here: SQL> SELECT SUM(value) "Data Requests" 2 FROM v$sysstat 3 WHERE name IN ('db block gets', 'consistent gets'); Data Requests ------------ 5105 You can add more free lists by re-creating the table with a larger value for the FREELISTS storage parameter. You may want to increase this parameter to the number of concurrent INSERT transactions that you expect to see. Although there usually is not a problem with free lists, monitoring them periodically will alert you if the system load has increased to where free lists are a problem. SummaryThis chapter looked at several areas you can improve in the Oracle instance. Most of these areas have a general theme; this theme relates to the fact that disk I/O is many times slower than memory. If you can optimize an instance to take advantage of this fact, you can achieve optimal performance. Here is a summary of the goals discussed in this chapter:
These areas of instance tuning can all help the overall performance of the system. The next chapter looks at some additional areas where you can change the system to increase performance.
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