Oracle SQL Tuning Tips
consideration when writing an SQL statement is that it returns a correct result. The second is that it be the most efficient for a given situation. You can use many different SQL statements to achieve the same result. It is often the case that only one statement will be the most efficient choice in a given situation.
Remember that processing SQL is a sequence of Parse (syntax check and object resolution), Execution (required reads and writes), and Fetch (row results retrieved, listed, sorted, and returned). SQL “tuning” consists, quite simply, of reducing one or more of them.
Note: generally Parse is the greatest time and resource hog. Parse overhead can be minimized by the use of Procedures, Functions, Packages, Views, etc.
Inadequate performance can have a significant cost impact on your business. A poor performing system and application can result in customer dissatisfaction, reduced productivity, and high costs. It is absolutely critical that the system’s performance is operating at its peak levels.
Following are some general tips that often increase SQL statement efficiency. Being general they may not apply to a particular scenario. Read more…
Oracle Data Export and Import utility
The Import and Export utilities work together; Export sends database definitions and actual data to an export file and Import can read the file to perform many different tasks. You can use Export and Import for many important database tasks, such as restoring a table, generating CREATE scripts, copying data among Oracle databases, migrating among Oracle versions, and moving tables from one schema to another.
Oracle’s export (exp) and import (imp) utilities are used to perform logical database backup and recovery. When exporting, database objects are dumped to a binary file which can then be imported into another Oracle database.
These utilities can be used to move data between different machines, databases or schema. However, as they use a proprietary binary file format, they can only be used between Oracle databases. One cannot export data and expect to import it into a non-Oracle database.
Various parameters are available to control what objects are exported or imported. To get a list of available parameters, run the exp or imp utilities with the help=yes parameter i.e. “exp help=yes” or “imp help=yes“.
The export/import utilities are commonly used to perform the following tasks: Read more…
/*+ hint */
/*+ hint(argument) */
/*+ hint(argument-1 argument-2) */
All hints except /*+ rule */ cause the CBO to be used. Therefore, it is good practise to analyze the underlying tables if hints are used (or the query is fully hinted.
There should be no schema names in hints. Hints must use aliases if alias names are used for table names. So the following is wrong:
select /*+ index(scott.emp ix_emp) */ from scott.emp emp_alias
better:
select /*+ index(emp_alias ix_emp) */ … from scott.emp emp_alias
Why using hints
Read more…
