Blogs

Tuning SQL with dynamic sampling

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Another example of what I think of as "the self-tuning database". Setting optimizer_dynamic_sampling=11 can fix many performance problems, without the DBA needing to use his brain at all.

Book review: Kevin Meade, Oracle SQL Performance Tuning and Optimization

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Excellent exposition of a very effective SQL tuning metodology

Oracle External Tables

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 The Oracle external tables feature allows us to access data in external sources as if it is a table in the database.
 External tables are read-only.
 No data manipulation language (DML) operations is allowed on an external table.
 An external table does not describe any data that is stored in the database.

Hash join anti vs Nested loop join anti

This post shows you details about a specific case where 'hash anti join' is defeated by 'nested loop anti join'.
The initial problem came to light in a very large BW system running on Oracle 11.2.0.4 when several BW loads (making use of older data in the BW system) reported missing dimension ids in the dimension tables.

Redo and undo volumes - take two

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Following a question on OTN https://community.oracle.com/message/12801175 I did another test on redo and undo, just to prove that frequent COMMIT can be bad for performance. The results surprised me. I expected that row-by-row commit would be worse then a single commit at the end of a multi-row transaction, but I hadn't expected it to be this bad. As well as being much slower, both undo and redo volumes are vastly greater.

Software Review - Stellar Phoenix Oracle Database Recovery Software

The demand of Oracle database is very high and because of high demand, its security becomes the most concerned part of its users. Backup is the initial process you can do for your database security. However, at times, taking backup is also not sufficient and issues like backup file corruption, database damage due to virus, etc. takes place and data loss occurs. Therefore it's always better to have a utility to repair your damaged or corrupt Oracle Database Files and reconstruct its objects.

V$RESERVED_WORDS & X$KWDDEF - Interesting facts!

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It's a lazy Friday and I saw an interesting question in Stack Overflow about "Why are there two “null” keywords in Oracle's v$reserved_words view?" And I spent next 2 hours digging into knowing the reason. Here are my findings:

We need to understand how to interpret the view v$reserved _words. To determine whether a particular keyword is reserved in any way, check the RESERVED, RES_TYPE, RES_ATTR, and RES_SEMI columns.

Redo and undo volumes

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How much undo and redo does Oracle generate for different operations? More than you might think.

Using reverse key indexes to solve buffer busy wait problems

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Buffer busy wait and related events can cripple performance of concurrent inserts. Bad in a single instance database, far worse in a RAC (think "gc buffer busy"). Often the problem is because of a primary key populated from a sequence. Reversing the index can fix this problem.

Using hash clusters to solve buffer busy wait problems

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Concurrent inserts into a table will often result in crippling buffer busy wait problems as sessions serialize on access to the last block(s) of the table segment. Using hash clusters can remove the issue.

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