WAL questions
От | Robert B. Easter |
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Тема | WAL questions |
Дата | |
Msg-id | 0101082321251P.09559@comptechnews обсуждение исходный текст |
Ответы |
Re: WAL questions
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Список | pgsql-general |
What is there for a user or admin or programmer to know about the new WAL stuff? What all does it do? Does it allow for an audit file to be created, which can be used to playback and/or rewind the transactions on the database by user/admin commands? How do checkpoints limit or affect how far back recovery is possible (if at all)? When is a checkpoint made? Does it allow for online recovery or only offline? What are the settings/parameters that control it (if any, like size of log at which to cut off a new one)? Can the WAL files that are made be read by humans and where are they stored? How transparent is this feature? Maybe I'm confused! I have some familiarity with a mainframe database that made audit tapes of all transactions. A nightly full dump was also made. Kinda old stuff. The tapes were kept for something like 2 weeks before being recycled. If the database crashed, it was possible to restore the database back to any time by using a full dump and some audit tapes. The dumps and audit tapes were specific to a database, not the whole DBMS. Other databases could be up and running normally while one was being rolled back and then forward again after fixing some problem. Even the one being restored could be online, queuing or processing some queries until the recovery was done. Something like that, it was a hospital environment. How does WAL compare to any of this, if at all? Can WAL be described as a deferred fsync of a batch of transactions? -- -------- Robert B. Easter reaster@comptechnews.com --------- -- CompTechNews Message Board http://www.comptechnews.com/ -- -- CompTechServ Tech Services http://www.comptechserv.com/ -- ---------- http://www.comptechnews.com/~reaster/ ------------
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