Log shipping ultimately
relies on a file transfer of a transaction log backup. The transfer of that file is not guaranteed.
If it fails for some reason, you must restart it manually (or use some sort of scripting
retry process). There is no automated method for ensuring the file is copied successfully.
Database mirroring, on the other hand, uses a queuing technology to guarantee the
transfer of information. Message queuing, as it??™s usually referred to, is only concerned
with the transfer of a piece of information from point A to point B. Figure 8-9 shows the
basics of message queuing.
Figure 8-9. The basic steps involved in message queueing
Figure 8-9 illustrates the following steps:
1. A database, or some other application, writes a piece of information to its local
message queue.
2. The first message queue contacts the remote queue, signaling an attempt to send
a message. It then copies the information.
3. At any time, the second database or application may retrieve the information,
which is now stored in the remote queue.
4. Once the data is received, the remote queue signals the local queue to confirm
receipt.
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