Tip

Find the most I/O-intensive SQL statements

This tip helps you in identifying "expensive" SQL statements running on your Oracle system and identifies the reasons for them being so poorly performing. It might indicate poor coding or inappropriate usage of indexes in these statements, which can then be tuned. As always, execute this script on your development system before trying it on your production system. It has been tested on Oracle 8, 8i and 9i. It is to be executed under SQL*PLUS with user INTERNAL.

-- Top 30 I/O Intensive SQL Statements Identification : top30iosql.sql
set linesize 80
set pagesize 58
set heading on
set serveroutput on

spool top30iosql.txt

declare
cursor curs1 is
select executions, disk_reads, buffer_gets, first_load_time, sql_text
from v$sqlarea order by disk_reads / decode(executions,0,1,executions) desc;
stmnt_ctr number(3);
wrt1 number(3);

begin
dbms_output.enable(50000);
stmnt_ctr := 0;

for inrec in curs1 loop
stmnt_ctr := stmnt_ctr + 1;
if stmnt_ctr >= 31 then
exit;
end if;

dbms_output.put_line('--------------------------------------' ||
'--------------------------------------');
dbms_output.put_line('SQL Stmnt Number: ' || to_char(stmnt_ctr));
dbms_output.put_line('--------------------------------------' ||
'--------------------------------------');
dbms_output.put_line('Executions : ' ||
to_char(inrec.executions));
dbms_output.put_line('Disk Reads : ' || to_char(inrec.disk_reads) ||
' Buffer Gets : ' || to_char(inrec.buffer_gets));
dbms_output.put_line('First Load Time: ' || inrec.first_load_time);
dbms_output.put_line('SQL Statement-------->');
wrt1

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:= 1; while wrt1 <= ceil(length(inrec.sql_text) / 72) loop dbms_output.put_line('.....' || substr(inrec.sql_text,((wrt1-1)*72)+1,72)); wrt1 := wrt1 + 1; end loop; dbms_output.put_line('--------------------------------------' || '--------------------------------------'); dbms_output.put_line(' '); end loop; end; / spool off set serveroutput off set termout on
Now Edit/view The output file top30iosql.txt in suitable viewer of your O/s and finetune... Best of Luck!

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This was first published in October 2003

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