Alter Index Rebuild Online
My database is release 10gR2. I sometimes execute command ALTER INDEX <index name> REBUILD ONLINE on indexes that are 500 MB in size. It takes about ten minutes to run the command. The database alert log shows no activity for the first six minutes, and DML is allowed on the associated table. At about minute seven the alert log shows the first in a series of five switches of the online redo logs. They are each 100 MB.
During the time that the online redo logs are switching, sessions executing DML are blocked from completing. When the new version of the index has been created the online redo logs stop switching, the original copy of the index disappears, the ALTER INDEX command ends, and the blocking of DML ceases.
I have read that DML statements are not affected by the execution of an ALTER INDEX REBUILD ONLINE, but experience shows the blocking of sessions described above. Can someone explain to me what takes place during the various stages of the index rebuild? Is there something I can do to eliminate the blocking of DML statements during the period when online redo logs switch?
Thank you,
Bill