By Mark Gurry
Probably the most very important demanding situations confronted by way of Oracle database directors and Oracle builders is the necessity to track SQL statements so they execute successfully. during this e-book, Mark Gurry stocks his in-depth wisdom of Oracle's SQL assertion optimizers. Mark's wisdom is the results of many hard-fought tuning battles in the course of his a long time of delivering Oracle tuning providers to consumers. Mark offers insights into the workings of the rule-based optimizer that move well past what the foundations inform you. Mark additionally offers ideas to many universal difficulties that happen with either the rule-based and cost-based optimizers. as well as the explicit problem/solution situations for the optimizers, Mark offers a couple of convenient SQL tuning advice. He discusses a few of the optimizer tricks, telling you once they can be utilized to strong impact. eventually, Mark discusses using the DBMS_STATS package deal to control database facts, and using outlines to specify execution plans for SQL statements in third-party functions that you just cannot differently alter.
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Additional resources for Oracle SQL Tuning Pocket Reference
Sample text
It is great to identify that we are using a nested loop when we shouldn't be, but what can we do about it? The answer is thatyou can consider using hints such as USE_NL, USE_HASH, or USE_MERGE. Hints are fine, but what if you are running packaged software and can't use hints? Perhaps you can create a view for reporting purposes, and place hints in the view. If you are running the rule-based optimizer, you can change to the cost-based optimizer. The cost-based optimizer has the intelligence to work out which join method is the best to use in a given situation.
Following are two sharable SQL statements: SELECT * FROM emp WHERE emp_no = :B1; Bind value: 123 SELECT * FROM emp WHERE emp_no = :B1; Bind value: 987 These statements are shareable because bind variables have been used, making the statements themselves identical. The actual bind values do not result in one statement being different from the other. Following are two non-sharable SQL statements. These statements are not sharable because bind variables have not been used, and the resulting hardcoded values make the statements different from each other.
Ideally, Oracle receives the ACCT_ADDRESS rows for the relevant account, and then joins to the ADDRESS table to determine if the addresses are in Washington. However, because so many tables are being joined, the cost-based optimizer will often process F and G independently of the other tables and then merge the data at the end. The result of joining F and G first is that all address that are in the state of Washington must be selected. That process could take several minutes, causing the overall runtime to be far beyond what it would have been if Oracle had driven all table accesses from the A table.