workarea executions

Hi,

in documentation I saw the following :

SELECT name profile, cnt, DECODE(total, 0, 0, ROUND(cnt*100/total)) percentage

  FROM (SELECT name, value cnt, (SUM(value) over ()) total

  FROM V$SYSSTAT

WHERE name

  LIKE 'workarea exec%');

The output of this query might look like the following:

PROFILE                                    CNT PERCENTAGE
----------------------------------- ---------- ----------
workarea executions - optimal             5395         95
workarea executions - onepass              284          5
workarea executions - multipass              0          0

What are the meanings of workarea executions  onepass  and multipass  and optimal  ?

optimal ? Comparing to what ? How is it defined ?

I looked for in all docs , I can not see.

Thank you.