Persistent variables #3563
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Persistent variables #3563
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This PR completes the persistent variables story where the engine will persist variables only if they are configured with a storage driver.
Before this PR, the entire memory register was serialized as part of the workflow instance, which is problematic for values that are supposed to have a transient lifetime (eg. streams, large data and non-serializable objects).
After this PR, none of the contents of the register is persisted. In order to persist a value, one needs to use a Variable AND configure it with a storage driver.
Currently, only two such driver types exist:
The Memory driver stores values in a local dictionary and lives for as long as the application does.
The Workflow driver stores the variable inside of the workflow instance document itself. This means that the variable value must be serializable.
Future drivers may include Redis, Blob storage, Disk storage, etc.