And let's create a table of accounts, same as in the last article. Indeed, if xmax in a tuple matches an active (not yet completed) transaction and we want to update this very row, we need to wait until the transaction completes, and no additional indicator is needed. And this very number xmax is used to indicate a lock. This ID shows that the transaction deleted the tuple. The UPDATE command itself selects the minimum appropriate locking mode rows are usually locked in the FOR NO KEY UPDATE mode.Īs you remember, when a row is updated or deleted, the ID of the current transaction is written to the xmax field of the current up-to-date version.
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