How to Find Slow SQL: Databases for Developers: Performance #9
In order to tune SQL, you need to know what the slow statement is. But often you're just told that "the database" is slow!
To find the slow components, you need a breakdown of how long each piece of code takes to execute. You can do this in Oracle Database using:
A SQL trace
The PL/SQL hierarchical profiler
This video shows you how to do these with Oracle SQL Developer.
The script to spool the trace file is:
-----
set serveroutput off
set pagesize 0
set echo off
set feedback off
set trimspool on
set heading off
set tab off
set long 1000000
spool c:\temp\student_trace.trc
select payload
from v$diag_trace_file_contents
where trace_filename = (
select substr (
value,
instr ( value, '/', -1 ) + 1
) filename
from v$diag_info
where name = 'Default Trace File'
)
order by line_number;
spool off
-----
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The Magic of SQL with Chris Saxon
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