70 lines
1.7 KiB
Plaintext
70 lines
1.7 KiB
Plaintext
.\" This is -*-nroff-*-
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.\" XXX standard disclaimer belongs here....
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.\" $Header: /cvsroot/pgsql/doc/man/Attic/create_version.l,v 1.1.1.1 1996/08/18 22:14:22 scrappy Exp $
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.TH "CREATE VERSION" SQL 01/23/93 Postgres95 Postgres95
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.SH NAME
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create version \(em construct a version class
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.SH SYNOPSIS
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.nf
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\fBcreate version\fP classname1 \fBfrom\fP classname2 [\fB[\fPabstime\fB]\fP]
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.fi
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.SH DESCRIPTION
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.IR "Currently, the versioning facility is not working."
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.PP
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This command creates a version class
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.IR classname1
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which is related
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to its parent class,
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.IR classname2 .
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Initially,
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.IR classname1
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has the same contents as
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.IR classname2.
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As updates to
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.IR classname1
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occur, however,
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the content of
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.IR classname1
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diverges from
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.IR classname2.
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On the other hand, any updates to
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.IR classname2
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show transparently through to
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.IR classname1 ,
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unless the instance in question has already been updated in
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.IR classname1 .
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.PP
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If the optional
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.IR abstime
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clause is specified, then the version is constructed relative to a
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.BR snapshot
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of
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.IR classname2
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as of the time specified.
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.PP
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Postgres uses the query rewrite rule system to ensure that
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.IR classname1
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is differentially encoded relative to
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.IR classname2.
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Moreover,
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.IR classname1
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is automatically constructed to have the same indexes as
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.IR classname2 .
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It is legal to cascade versions arbitrarily, so a tree of versions can
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ultimately result. The algorithms that control versions are explained
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in [ONG90].
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.SH EXAMPLE
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.nf
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--
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--create a version foobar from a snapshot of
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--barfoo as of January 17, 1990
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--
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create version foobar from barfoo [ "Jan 17 1990" ]
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.fi
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.SH "SEE ALSO"
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create view(l), merge(l).
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.SH "BUGS"
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Snapshots (i.e., the optional
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.IR abstime
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clause) are not implemented in Postgres.
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