Row movement in oracle

Row movement is associated with partitioned and non-partitioned tables but is mostly associated with non-partitione tables. For partitioned tables when ROW MOVEMENT is enabled users have the ability to update partitioning key columns in such a way that a row no longer belongs in its current partition, causing such rows to migrate to the appropriate partition. Row movement is enabled at the table level and is disabled by default.

For example:

CREATE TABLE sales(
sale_id NUMBER NOT NULL,
sale_date DATE,
prod_id NUMBER,
qty NUMBER)
PARTITION BY RANGE(prod_id)
(PARTITION salesp1 VALUES LESS THAN(10),
PARTITION salesp2 VALUES LESS THAN(20),
PARTITION salesp3 VALUES LESS THAN(30),
PARTITION salesp4 VALUES LESS THAN(40))

Partition salesp1 above will have prod_id values upto 9 (since partition high values are non-inclusive). If you issue an update statement like this:

SQL> update sales set prod_id = 15 where prod_id = 5;

For the above statement to succeed, oracle has to migrate the row that you are updating from partition salesp1 to salesp2. Under those circumstances, it will raise this error:
ORA-14402: updating partition key column would cause a partition change

You can overcome the above error by issuing this statement:

SQL> ALTER TABLE sales ENABLE ROW MOVEMENT;

-- You can now issue the update statement successfully

SQL> update sales set prod_id = 15 where prod_id = 5;
4 rows updated
SQL> commit;

Row movement is allowed for non-partitioned tables starting 9i. Row movement comes in to affect for non-partitioned tables when you do operations like table compression.
Couple of things to be beware of with row movement are
(1) Oracle will do a delete and insert in the background which can cause
performance issues and
(2) The rowid for the row that went through row migration will change which can potentially cause problems if the application uses static rowids for data access.

I don't remember which URL I got this info from.But it is really good .If someone can tell me the URL I will remove this article and post the link here

Comments

Post a Comment

Popular posts from this blog

ORA-00923: FROM keyword not found where expected

Problem Symptom While performing a simple select statement it fails with error ORA-00923: FROM keyword not found where expected like below. SQL> select 48*1024*1024*1024 decimal from dual; select 48*1024*1024*1024 decimal from dual * ERROR at line 1: ORA-00923: FROM keyword not found where expected Cause of the problem The ORA-00923 can be caused by two different reasons. 1)Oracle itself expect FROM keyword in the position but it could not find any. Like below, SQL> select 48*1024 om dual; select 48*1024 om dual * ERROR at line 1: ORA-00923: FROM keyword not found where expected As no from keyword found so error arises. Oracle expected from in place of keyword dual. 2)The secong cause can sometimes mislead you. Like in case of SQL> select 48*1024*1024*1024 decimal from dual; select 48*1024*1024*1024 decimal from dual * ERROR at line 1: ORA-00923: FROM keyword not found where exp
Read more

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