Apress.Expert.Oracle.Database.Architecture.9i.and.10g.Programming.Techniques.and.Solutions.Sep.2005

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CHAPTER 4 ■ MEMORY STRUCTURES
or a.name like '%direct temp%')
and b.sid = c.sid
and c.username is not null
group by 'total: ' || a.name
) curr_stats
on (sess_stats.name = curr_stats.name)
when matched then
update set diff = curr_stats.value - sess_stats.value,
value = curr_stats.value
when not matched then
insert ( name, value, diff )
values
( curr_stats.name, curr_stats.value, null )
/
I simply added the UNION ALL section to capture the total PGA/UGA and sort writes by
summing over all sessions, in addition to the statistics for a single session. I then ran the following
SQL*Plus script in that particular session. The table BIG_TABLE had been created
beforehand with 50,000 rows in it. I dropped the primary key from this table, so all that
remained was the table itself (ensuring that a sort process would have to be performed):
set autotrace traceonly statistics;
select * from big_table order by 1, 2, 3, 4;
set autotrace off
■Note The BIG_TABLE table is created as a copy of ALL_OBJECTS with a primary key, and it can have as
many or as few rows as you like. The big_table.sql script is documented in the “Setting Up” section at
the beginning of this book.
Now, I ran that small query script against a database with a PGA_AGGREGATE_TARGET of
256MB, meaning I wanted Oracle to use up to about 256MB of PGA memory for sorting. I set
up another script to be run in other sessions to generate a large sorting load on the machine.
This script loops and uses a built-in package, DBMS_ALERT, to see if it should continue processing.
If it should, it runs the same big query, sorting the entire BIG_TABLE table. When the
simulation was over, a session could signal all of the sorting processes, the load generators,
to “stop” and exit. The script used to perform the sort is as follows:
declare
l_msg long;
l_status number;
begin
dbms_alert.register( 'WAITING' );
for i in 1 .. 999999 loop
dbms_application_info.set_client_info( i );
dbms_alert.waitone( 'WAITING', l_msg, l_status, 0 );