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 Isolation Level 1 or 10 

If you specify the isolation level 1 or 10 (committed), then a shared lock is assigned to the transaction for a read row R1 of a table. When the next row R2 in the same table is read, the lock on R1 is released and a shared lock is assigned to the transaction for the row R2.

When you retrieve data with a QUERY statement, the database system ensures that, at the time each row is read, no exclusive lock has been assigned to other transactions for the given row. It is impossible to predict, however, whether a query statement causes a shared lock for a row of the specified table or not and for which row this may occur.

When rows are inserted, updated or deleted, implicit exclusive locks are assigned to the transaction for the rows concerned. These cannot be released until the end of the transaction.

 

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