Row chaining

Hi,

Please anyone explain me,what is row chaining & row migration?

Thanks,
Malru

When a row is initially inserted into a table and the row is too large to fir in one data block, the row is "chained" in multiple blocks.
When a row is already inserted in the bklock in it fits in it, but later it is updated and becomes bigger and does not fit any more in the block - the entire block is "migradted" to another block. The initial block contains a link to the migrated block so the initial rowid is not changed.
Both of these occurences decrease I/O performance when reading these blocks.

Seems to me that you've posted a lot of threads in a short space of time asking questions, mostly about fairly basic DBA tasks. Have you tried searching the web first?

rhetorical question if ever I saw one there