62 lines
1.7 KiB
Plaintext
62 lines
1.7 KiB
Plaintext
.\" This is -*-nroff-*-
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.\" XXX standard disclaimer belongs here....
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.TH PURGE SQL 11/05/95 Postgres95 Postgres95
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.SH NAME
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purge \(em discard historical data
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.SH SYNOPSIS
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.nf
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\fBpurge\fR classname [ \fBbefore\fR abstime ] [ \fBafter\fR reltime ]
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.fi
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.SH DESCRIPTION
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.BR Purge
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allows a user to specify the historical retention properties of a
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class. If the date specified is an absolute time such as \*(lqJan 1
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1987\*(rq, Postgres will discard tuples whose validity expired before
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the indicated time.
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.BR Purge
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with no
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.IR before
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clause is equivalent to \*(lqpurge before now\*(rq. Until specified
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with a purge command, instance preservation defaults to
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\*(lqforever\*(rq.
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.PP
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The user may purge a class at any time as long as the purge date never
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decreases. Postgres will enforce this restriction, silently.
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.PP
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Note that the
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.BR purge
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command does not do anything except set a parameter for system
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operation. Use
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.IR vacuum (l)
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to enforce this parameter.
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.SH EXAMPLE
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.nf
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--
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--Always discard data in the EMP class
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--prior to January 1, 1989
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--
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purge EMP before "Jan 1 1989"
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.fi
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.nf
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--
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--Retain only the current data in EMP
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--
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purge EMP
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.fi
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.SH "SEE ALSO"
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vacuum(l).
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.SH "BUGS AND CAVEATS"
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Error messages are quite unhelpful. A complaint about
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\*(lqinconsistent times\*(rq followed by several nine-digit numbers
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indicates an attempt to \*(lqback up\*(rq a purge date on a relation.
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.PP
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You cannot purge certain system catalogs (namely, \*(lqpg_class\*(rq,
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\*(lqpg_attribute\*(rq, \*(lqpg_am\*(rq, and \*(lqpg_amop\*(rq) due
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to circularities in the system catalog code.
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.PP
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This definition of the
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.BR purge
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command is really only useful for non-archived relations, since
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tuples will not be discarded from archive relations (they are
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never vacuumed).
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