The number of rows affected by an SQL statement
is something that has been available to Oracle for
a long time. Monitoring just records that number in
a memory structure.
I'd guess the memory structure is a hash table, and
there are no latches protecting it (so I've heard, and
I can't see any in x$ksllt) so the memory update is
(a) rapid (b) subject to lost data.
At regular intervals (3 hours for older versions,
15 minutes for newer) smon copies the data
from memory to the mon_mod$ table.
The overhead is small.
But:
a) The results are not corrected on rollback
b) Concurrent changes to the count get lost
c) There was at least one bug relating to partitioned
tables with large numbers of partitions reported
on metalink some time ago.
Regards
Jonathan Lewis
http://www.jlcomp.demon.co.uk
The educated person is not the person
who can answer the questions, but the
person who can question the answers -- T. Schick Jr
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The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/faq/ind_faq.html
----- Original Message -----
To: "Multiple recipients of list ORACLE-L" <[EMAIL PROTECTED]>
Sent: Thursday, January 22, 2004 1:44 PM
> Especially on high transaction tables? I dont have any numbers for
transactions/second since we are not live. Any known issues? how does the
monitoring work? Does it use an internal trigger and then use SQL to write
the data? or does the monitoring data bypass the SQL layer and get written
directly to the block?
>
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Author: Jonathan Lewis
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