crystal reports barcode font formula Sessions with a High Number of Hard Parses in Font

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Sessions with a High Number of Hard Parses
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The query in Listing 20-3 enables you to find out how the hard parses compare with the number of executions since the instance was started. It also tells you the session ID for the user using the SQL statements.
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CHAPTER 20 PERFOR MAN CE TUNING: TUNING THE INSTA NCE
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Listing 20-3. Determining Sessions with a High Number of Parses SQL> 2 3 4 5 6 7 8 9 10* SELECT s.sid, s.value "Hard Parses", t.value "Executions Count" FROM v$sesstat s, v$sesstat t WHERE s.sid=t.sid AND s.statistic#=(select statistic# FROM v$statname where name='parse count (hard)') AND t.statistic#=(select statistic# FROM v$statname where name='execute count') AND s.value>0 ORDER BY 2 desc; Hard Parses ----------70750 12188 3555 3265 1579 Executions Count ---------------3638104 262881 5895488 2758185 2389953
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SID ---------1696 1750 1759 1757 1694 . . . SQL>
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Using the CURSOR_SPACE_FOR_TIME Parameter
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By default, cursors can be deallocated even when the application cursors aren t closed. This forces an increase in Oracle s overhead because of the need to check whether the cursor is flushed from the library cache. The parameter that controls whether this deallocation of cursors takes place is the CURSOR_SPACE_FOR_TIME initialization parameter, whose default value is FALSE. If you set this parameter to TRUE, you ensure that the cursors for the application cannot be deallocated while the application cursors are still open. The initialization parameter in the init.ora file should be as follows: CURSOR_SPACE_FOR_TIME=TRUE
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If you want to set this parameter, make sure that you have plenty of free shared pool memory available, because this parameter will use more shared pool memory for saving the cursors in the library cache.
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Using the SESSION_CACHED_CURSORS Parameter
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Ideally, an application should have all the parsed statements available in separate cursors, so that if it has to execute a new statement, all it has to do is pick the parsed statement and change the value of the variables. If the application reuses a single cursor with different SQL statements, it still has to pay the cost of a soft parse. After opening a cursor for the first time, Oracle will parse the statement, and then it can reuse this parsed version in the future. This is a much better strategy than re-creating the cursor each time the database executes the same SQL statement. If you can cache all the cursors, you ll retain the server-side context, even when clients close the cursors or reuse them for new SQL statements. You ll appreciate the usefulness of the SESSION_CACHED_CURSORS parameter in a situation where users repeatedly parse the same statements, as happens in an Oracle Forms-based application when users switch among various forms. Using the SESSION_CACHED_CURSORS parameter ensures that for
CH A PT ER 2 0 PERF O RMAN CE TUNI NG: TUN ING TH E I NS TA NCE
any cursor for which more than three parse requests are made, the parse requests are automatically cached in the session cursor cache. Thus new calls to parse the same statement avoid the parsing overhead. Using the initialization parameter SESSION_CACHED_CURSORS and setting it to a high number makes the query processing more efficient. Although soft parses are cheaper than hard parses, you can reduce even soft parsing by using the SESSION_CACHED_CURSORS parameter and setting it to a high number. You can enforce session caching of cursors by setting the SESSION_CACHED_CURSORS in your initialization parameter file, or dynamically by using the following ALTER SESSION command: SQL> ALTER SESSION SET SESSION_CACHED_CURSORS = value; You can check how good your SESSION_CACHED_CURSORS parameter value is by using the V$SYSSTAT view. If the value of session cursor cache hits is low compared to the total parse count for a session, then the SESSION_CACHED_CURSORS parameter value should be bumped up. The perfect situation is where a SQL statement is soft parsed once in a session and executed multiple times. For a good explanation of bind variables, cursor sharing, and related issues, please read the Oracle white paper Efficient use of bind variables, cursor_sharing and related cursor parameters (http://otn.oracle.com/deploy/performance/pdf/cursor.pdf).
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