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Posts Tagged ‘optimizer’

generate dumps – overview

13. September 2011 Leave a comment

Some nice – important dump options 🙂

and still under constuction

find sga ID

in Unix environments with mutiple instances running within the same os-use (e.g. oracle) you cannot see which memory segment is allocated to which instance.

sqlplus  / as sysdba
oradebug setmypid
oradebug ipc
oradebug tracefile_name

the column Shmid shows the dependend memory structures

Read more…

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invalidate cursor in shared pool

Sometimes it’s necessary to invalidate a specific cursor in shared pool.

In the past you had to flush the complete shared pool – which caues ALL sql statements were flushed 😦

In the package dbms_shared_pool you can flush a SINGLE cursor.

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sql plan management – how to fix an execution plan

in the past stored outlines were used to fix execution plans
in 11g the next level to control execution plans is implemented
its possible to force the optimizer to use one or more execution plans for a statement, uncontrolled plan changes are disabled.

take a closer look at the following examples – test it!
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event 10053 – obtaining optimizer computations

to see how the oracle optimizer generates the execution plan  use the event 10053

alter session set max_dump_file_size = unlimited;
alter session set tracefile_identifier='tr10053';
alter session set events='10053 trace name context forever, level 1';

the tracefile will be written to user_dump_dest (10.2) or in <diag_dest>/rdbms/<database>/<instance>/trace