A waveguide is a structure that is used to guide electromagnetic waves such as radio waves and microwaves. It serves to channel radio waves in a specific dimension and in a specific shape, allowing them to travel longer distances from the source toward the antenna and to travel only in a predetermined area in order to avoid interference and...
The problems caused by concurrency are even more important than the ability to support concurrent transactions. For example, when one user is changing data but has not yet saved (committed) that data, then the database should not allow other users who query the same data to view the changed, unsaved data. Instead the user should only view the original data.
Almost all databases deal with concurrency the same way, although the terminology may differ. The general principle is that changed but unsaved data is held in some sort of temporary log or file. Once it is saved, it is then written to the database’s physical storage in place of the original data. As long as the user performing the change has not saved the data, only he should be able to view the data he is changing. All other users querying for the same data should view the data that existed prior to the change. Once the user saves the data, new queries should reveal the new value of the data.
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