Здравствуйте, Alexey Shirshov, Вы писали:

AS>Откуда дровишки? Или сам сочиняешь?
Дровишки от одного, всем известного верблюда, тоесть из теории RDBMS.

Вот первое, что под руку подвернулось:

Write Ahead Logging (WAL) is a standard approach to transaction logging. Its detailed description may be found in most (if not all) books about transaction processing. Briefly, WAL's central concept is that changes to data files (where tables and indices reside) must be written only after those changes have been logged — that is, when log records have been flushed to permanent storage. When we follow this procedure, we do not need to flush data pages to disk on every transaction commit, because we know that in the event of a crash we will be able to recover the database using the log: any changes that have not been applied to the data pages will first be redone from the log records (this is roll-forward recovery, also known as REDO) and then changes made by uncommitted transactions will be removed from the data pages (roll-backward recovery — UNDO).

(с) Vadim Mikheev and Oliver Elphick
PostgreSQL 7.1.1 Documentation