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Manual Locking and User-Defined Locks- Locking and Latching
So far, we have looked mostly at locks that Oracle places for us transparently. When we update a table, Oracle places a TM lock on…
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Performance/Scalability Comparison- Locking and Latching
Table 6-1 summarizes the CPU usage by each implementation, as well as the latching results as we increase the number of users beyond two. As…
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DDL Locks- Locking and Latching-1
DDL locks are automatically placed against objects during a DDL operation to protect them from changes by other sessions. For example, if I perform the…
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DDL Locks- Locking and Latching-2
A view that is invaluable for looking at this information is DBA_DDL_LOCKS. There is no V$ view. The DBA_DDL_LOCKS view is built on the more…
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Optimistic or Pessimistic Locking? – Locking and Latching
So which method is best? In my experience, pessimistic locking works very well in Oracle (but perhaps not so well in other databases) and has…
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Blocked Inserts- Locking and Latching
There are a few times when an INSERT will block. The most common scenario is when you have a table with a primary key or…
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Blocked Merges, Updates, and Deletes- Locking and Latching-2
These full table locks are a short-term occurrence in Oracle 9i and above, meaning they need to be taken for the duration of the DML…
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TX (Transaction) Locks- Locking and Latching-1
A TX lock is acquired when a transaction initiates its first change. The transaction is automatically initiated at this point (you don’t explicitly start a…
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TX (Transaction) Locks- Locking and Latching-3
However, before we can say that we have a good understanding of how the row locking in Oracle works, we must look at one last…
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What Are Locks?- Locking and Latching-3
It was during a benchmark that I discovered just how wrong I was. In the early days of these databases, it was common for the…