A Question about Oracle SQL Statment processing

Dear Experts,

What are the genarel reasons for SQL Statments processing slowness of Oracle Database?
Additionally tell me,

(1).What is the effect of Memory for SQL Statement processing?
(2).Is there any relationship with undo tablespace and UPDATE Statements?

Thank You in advance.
Pradeep.
Pradeep SiriwardanaSystems EngineerAsked:
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Praveen Kumar ChandrashekatrDatabase Analysist Senior Commented:
some of the genral reasons for poor perforamce of SQL statements is

Bad Design
Poor coding
Old Statistics
less memory

check this doc for more detail info

http://www.dba-oracle.com/t_top_reasons_poor_performance.htm

(2).Is there any relationship with undo tablespace and UPDATE Statements?

when ever you update a row in a table, then the old value of the row is stored in your undo tablespace  for your rollback purpose.

Undo also provides read consistency for users who are querying rows involved in a DML transaction by another user or session. When one user starts to make changes to a table after another user has already begun a query against the table, the user issuing the query will not see the changes to the table until after the query has completed and the user issues a new query against the table.
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Wasim Akram ShaikCommented:
Regarding your first point

What is the effect of Memory for SQL Statement processing?

Detailed explanation can be found in burleson site..

http://www.dba-oracle.com/sql/t_sql_execution_steps_parsing_fetching.htm

2nd point, i agree with expert praveen..

further to this, refer to the blogs for detailed information

http://ora10g.com/6_1_undo.html
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