Creating attached indexes in an online environment

You can create attached indexes using the CREATE INDEX ONLINE statement, but the statement only operates when Dirty Read is the transaction isolation level.

The index creation takes an exclusive lock on the table and waits for all other concurrent processes scanning the table to quit using the index partitions before creating the attached index. If the table is being read or updated, the CREATE INDEX ONLINE statement waits for the exclusive lock for the duration of the lock mode setting.

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