Oracle-L: RE: Lite: Redo sequence# poll

From: John Kanagaraj <john.kanagaraj_at_hds.com>
Date: Mon, 11 Mar 2002 14:51:43 -0800
Message-ID: <F001.004250EF.20020311145143@fatcity.com>

Hi Jeremiah and list,

> Since people with undersized logfiles will come out on top, how about
> comparing current SCNs instead?

Nice catch, but when distributed databases are involved, the following applies:

Internal Operations Each committed transaction has an associated system change
number (SCN) to uniquely identify the changes made by the statements within that
transaction. In a distributed database, the SCNs of communicating nodes are coordinated when:
* A connection is established using the path described by one or more database
links
* A distributed SQL statement is executed * A distributed transaction is committed Among other benefits, the coordination of SCNs among the nodes of a distributed
database system allows global distributed read-consistency at both the statement
and transaction level. If necessary, global distributed time-based recovery can also
be completed.

All databases in a 'distributed' (i.e. connected) environment will co-ordinate with each other to bump up their SCNs to the highest value+ whenever a distributed SQL is involved. So, a large DSS type database that has a relatively lesser number of queries/commits (and thus a lower SCN rate) may have its SCN count bumped up by a short-query, active OLTP... Not to mention parameters such as COMMIT_POINT_STRENGTH that could influence this... The point is that this would probably not be a good measure of the 'activeness' of a database.

Btw, the v$database view will show this part of x$ktuxe. Be sure to set numwidth to a larger value.

> Also longest time since last startup would be interesting to see.

Now this would be an interesting one!

John Kanagaraj
Oracle Applications DBA
DBSoft Inc
(W): 408-970-7002

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The opinions and statements above are entirely my own and not those of my employer or clients ** -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: John Kanagaraj INET: john.kanagaraj_at_hds.com

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