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Data Warehouse |
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[SSIS] |
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Questions: |
Notes: |
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What are Asynchronous Components? |
The output of an asynchronous component uses a new buffer. It’s not possible to reuse the input buffer because an asynchronous component can have more or less output records than input records.
The only thing you need to remember is that synchronous components reuse buffers and therefore are generally faster than asynchronous components, that need a new buffer. |
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What is Data Isolation? |
Transactions specify an isolation level that defines the degree to which one transaction must be isolated from resource or data modifications made by other transactions.
Isolation levels are described in terms of which concurrency side-effects, such as dirty reads or phantom reads, are allowed. |
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What are the Isolation Levels? |
The Isolation levels are scaled from lowest to highest isolation:
i. The lowest level where transactions are isolated only enough to ensure that physically corrupt data is not read. All of the concurrency side effects can happen in read uncommitted, but there is no read locking or versioning, so overhead is minimized.
i. Database Engine default level
i. The highest level, where transactions are completely isolated from one another. Guarantees that a transaction will retrieve exactly the same data every time it repeats a read operation, but it does this by performing a level of locking that is likely to impact other users in multi-user systems. |
