WAL principle

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The so-called write ahead logging ( WAL ) is a procedure of the database technology which contributes to guaranteeing the atomicity and durability of transactions. It states that modifications must be logged before they are actually written (added to the database).

The WAL principle enables a so-called "update-in-place", i.e. H. the old version of a data record is overwritten by the new version in the same place. The main advantage of this is that index structures do not have to be updated during change operations, because the changed data records can still be found in the same place. A change must be logged beforehand in order to ensure that the change can be repeated in the event of an error.