Archive for April 3rd, 2009
Endless loops
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Imagine that we are developing an email server that keeps the outgoing messages in a database.
The server is always busy sending the messages if the outgoing queue is not empty. It may have up to 10 connections at once.
If the message is failed to be sent, it's reinserted to the end of the queue until the retry count is exceeded.
As soon as all messages from a batch succeed or fail to be sent, next 10 messages from the queue are fetched.
How do we write a query to fetch a batch of messages from the queue?
This all can be done in a single query run in a loop. No range checking, no reinserting.
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