Request Level Transactions

Request level transactions are used when the request is not in the scope of a global or local transaction, which implies "autoCommit" is "true". In a request level transaction, your application does not need to explicitly call commit or rollback, rather every command is assumed to be its own transaction that will automatically be committed or rolled back by the server.

The Teiid Server can perform updates through virtual tables. These updates might result in an update against multiple physical systems, even though the application issues the update command against a single virtual table. Often, a user might not know whether the queried tables actually update multiple sources and require a transaction.

For that reason, the Teiid Server allows your application to automatically wrap commands in transactions when necessary. Because this wrapping incurs a performance penalty for your queries, you can choose from a number of available wrapping modes to suit your environment. You need to choose between the highest degree of integrity and performance your application needs. For example, if your data sources are not transaction-compliant, you might turn the transaction wrapping off (completely) to maximize performance.

You can set your transaction wrapping to one of the following modes:

  1. ON: This mode always wraps every command in a transaction without checking whether it is required. This is the safest mode.

  2. OFF: This mode never automatically wraps a command in a transaction or check whether it needs to wrap a command. This mode can be dangerous as it will allow multiple source updates outside of a transaction without an error. This mode has best performance for applications that do not use updates or transactions.

  3. DETECT: This mode assumes that the user does not know to execute multiple source updates in a transaction. The Teiid Server checks every command to see whether it is a multiple source update and wraps it in a transaction. If it is single source then uses the source level command transaction. You can set the transaction mode as a property when you establish the Connection or on a per-query basis using the execution properties. For more information on execution properties, see the section Execution Properties

Multiple Insert Batches

When issuing an INSERT with a query expression (or the deprecated SELECT INTO), multiple insert batches handled by separate source INSERTS may be processed by the Teiid server. Care should be taken to ensure that targeted sources support XA or that compensating actions are taken in the event of a failure.

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