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Chapter 8. Transaction Logging This chapter describes the transaction logging facilty of CloudTran. The transaction logger keeps a copy of the transactions committed by CloudTran. All the objects that are sent to a persistent store, e.g. a database, will be recorded in the transaction log. Although all nodes in a CloudTran system - the nodes holding the in-memory data and the transaction buffer - should be run with one or more hot failover nodes, a complete failure will cause transactions to be lost from in-memory before they have been persisted to the persistent store. In theory, this is unlikely; in decision-makers' thinking, it looms large. In this case, CloudTran ensures you 'replay' the transaction log so that transactions that were committed during normal running are sent to the persistent store. This is very important because it means applications can carry on while information is being sent to the database - which is much slower than committing to memory. It also means that CloudTran doesn't have to keep to the transaction boundaries marked by the application. On persisting, CloudTran reorders transactions and sends them to the database in batches. In doing so, it makes sure that any rows that are affected by two different transactions are isolated on the way to the database.
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