Rebuilding Indexes

when to rebuild index

the index may be rebuild in following situations

1)If the existing index is to moved to different tablespace.
2) If index contains many deleted entries.
3) If the table of index has been moved to another tablespace.

in case of rebuilding an index

1) A new index is built using an existing index as data source.
2)the older index is deleted after the new index is built.
3)queries can continue to use the existing index while the new index is being built.

example:

ALTER INDEX mytable_idx REBILD
TABLESPACE newtb;