when a row is created (ORA_ROWSCN Pseudocolumn)

To know the exact time of when a row is inserted or updated or deleted you have to use audit system or use logminer utility. But to use these two tool you have to configure your environment previously. However if you don't enable either audit option or supplemental logging (which is required for analysis in logminer) you can still get a rough idea about a row in a table about when it is modified/inserted more precisely the most recent change of a row.

This is possible by using ORA_ROWSCN psedocolumn.

•ORA_ROWSCN returns the conservative upper bound system change number (SCN) of the most recent change for each row.

•The resultant value of ORA_ROWSCN is not absolutely precise, because Oracle tracks SCNs by transaction committed for the block in which the row resides.

•But a better result of the row chaging time of a table can by found by creating tables with row-level dependency tracking. This is done by CREATE TABLE ... ROWDEPENDENCIES statement. If you create your table with this statement then you can get more precise result.

•ORA_ROWSCN can't be used while querying view.

•It is not supported for external tables and also not supported for Flashback Query..

Example:
----------------
The get a rough idea of the rows of table a when the rows were created as well as SCN query as,
SQL> select scn_to_timestamp(ORA_ROWSCN), ORA_ROWSCN , a from a;

SCN_TO_TIMESTAMP(ORA_ROWSCN) ORA_ROWSCN A
--------------------------------------------------------------------------- ---------- ----------
09-JUL-08 06.53.59.000000000 AM 9020925 5
13-JUL-08 06.40.33.000000000 AM 9791113 1
13-JUL-08 06.40.33.000000000 AM 9791113 9

Comments

Post a Comment

Popular posts from this blog

How to make partitioning in Oracle more Quickly

As the table size grows and full table scans happens more frequently then there is no alternative than partitioning in oracle. Partition greatly enhance performance of a query. I will start my partitioning system simply with an example. In my database the following query took 30~35 seconds to complete. After partitioning the performance increased amazingly and it then took only 1 second. My query was, SELECT DISTINCT fs.type, fs.id , fs.pid, fs.cid , fs.cr_id, fs.created_date FROM summary fs where fs.id in (select fa.id from forms fa where fa.sar in (select la.sar from login la where la.login_id=1 and fa.created_date BETWEEN to_date('1-MAY-2008') AND to_date('21-SEP-2008') and fs.created_date BETWEEN to_date('1-MAY-2008') AND to_date('21-SEP-2008') ) )and mode=0; After seeing above query I decide to make range partition on column created_date both in summary table and forms table. Below is the list of procedur
Read more

Copy files between Unix and Windows with rcp

There are many third party tools by which you can copy files between windows and unix machine. Some common tools are winscp, SSHSecureShellClient etc. Instead of using any third party tool, you can use original unix and windows built-in tool to do the task. The RCP (Remote CoPy) is a standard UNIX tool and a Microsoft Windows 2000 tool that copies files/folder to and from computer running the RCP service. Before you can use the RCP tool from a Windows-based computer you must do something in your UNIX computer. you must turn on the RCP service and update the security files to allow the Windows-based computer to connect to your unix machine over this service. The following steps will help you. Step 01: Turn on RCP service on UNIX Host Turn on the RCP service on unix machine by using inetd: 1. Log on as root. 2. Edit the file /etc/Inetd.conf. 3. Uncomment the lines that start with shell and that start with exec. 4. Save the file. 5. Use ps -ef |grep inetd and determine inetd service p
Read more

ORA-04062: timestamp of procedure has been changed

Problem Description In the database I have created one procedure named a as below. create or replace procedure a(a number) as begin insert into t1 values(1); commit; end; / Now after creating database link using remote database machine whenever I access this procedure "A" it executes successfully and I get value "1" in table t1. Like below in example where orastdby_m is the database link, shaik is the schema name and value 1 is the argument value though argument value is not used in the procedure. SQL> exec shaik.a@orastdby_m(1); PL/SQL procedure successfully completed. Now in the source database machine I changed the procedure as below. Though you can change anything like any literal; adding space or remove space. I changed value to be inserted from 1 to 2. create or replace procedure a(a number) as begin insert into t1 values(2); commit; end; / Now in the other database whenever I execute the procedure using database link it throws error ORA-04062. But subseq
Read more