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To: postgres@postgres.Berkeley.EDU
Subject: time travel
Date: Wed, 09 Nov 1994 13:57:59 +0000
From: Giles Nelson <Giles.Nelson@cl.cam.ac.uk>
Message-ID: <"swan.cl.cam.:198030:941109135811"@cl.cam.ac.uk>
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Resent-Date: Wed, 09 Nov 94 06:00:31 -0800
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Hello all.

I have a query about the facilities POSTGRES gives for historical databases,
what the user manual terms as `time travel'.

Classes can be created to be archival or not. The default is not. Therefore
after instances are deleted, purged and the database vacuumed those instances
will have been physically deleted.

Alternatively a class may be defined as archival. Even after vacuuming
therefore deleted instances are still accessible.

The time stamp that POSTGRES appears to attach to each instance is what is
often termed `database time', that is the time at which the instance was
actually inserted into the database.

I would like to use the built-in facilities that POSTGRES has for time travel
but I wish to time stamp each instance with an `event time', that is the time
which is associated with the instance itself, such as a birth date.

My impression is that this is not possible and I will have to use a time
attribute within a relation. However I wondered if anyone else had experience
of doing directly and therefore retaining the use of built-in facilities.

Giles Nelson.

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