Topic: Backup & Recovery >> Row Migration and chaning !
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| Title: Row Migration and chaning ! |
| seema |
Posted: Sep 23, 2008 04:48:37 AM |
Total Post: 70
Joined: Jan, 2008
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Please tell me row migration and chaning is done by the dba or oracle itself???
If that work is done by dba then how to do this??? |
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 vino |
| Posted: Sep 23, 2008 11:55:14 AM |  |
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Total Post: 357
Joined: Aug, 2008
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Row Migration and Chaining is the concepts of Fragmentation. DBA should have to find whether the objects like table, index..etc gone in fragmentation or not. This is done by gathering statistics of each objects. If the statistics value is more than the threshold value then we can go for defragmenting it.
Regards.
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| scorpio |
| Posted: Sep 23, 2008 01:14:23 PM | |
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Total Post: 20
Joined: Sep, 2008
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The row is too large to fit into an EMPTY data block.In this Oracle stores the DATA for the row in a CHAIN of one or more Data BLOCKS.
CHAINING occurs when row is INSERTED or UPDATED
Migration :An UPDATE statement increases the amount of DATA in a ROW so that the Row NO LONGER FITS in to its DATA BLOCK.
Oracle tries to find another Blockwith enough free space to hold the entire row.If such block is available Oracle moves the entire ROW to the NEW BLOCK.Oracle keeps the original Row piece of a Migrated row row to POINT to the NEW BLOCK containing the actual row.The ROWID of the MIGRATED rows does not change.INDEXES are not updated and they point to the ORIGINAL row LOCATION.
DBA involve in identifiing this row C & M
we can detect the Migrated or chained rows in a TABLE or CLUSTER by using the following methods.
Using ANALYZE,REPORT.TXT and V$VIEWS.
SQL>ANALYZE TABLE SCHEMA_NAME.TABLE_NAME LIST CHAINED ROWS;
SQL>SLECT owner_name,table_name,head_rowid from chained_rows where TABLE_NAME = 'YOUR_TABLE_NAME';
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