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Re: AS OF queries

Konstantin Knizhnik <k.knizhnik@postgrespro.ru>

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From: Konstantin Knizhnik <k.knizhnik@postgrespro.ru>
To: Jeff Janes <jeff.janes@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, Laurenz Albe <laurenz.albe@cybertec.at>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2017-12-28T16:36:30Z
Lists: pgsql-hackers

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Attached please find new version of AS OF patch which allows to specify 
time travel period.
Older versions outside this period may be reclaimed by autovacuum.
This behavior is controlled by "time_travel_period" parameter.

Zero value of this parameter disables time travel and postgres behaves 
in standard way.
Actually you can still use AS AF construction but there is no warranty 
that requested versions are not reclaimed and result of query actually 
belongs to the specified time slice.

Value -1 means infinite history: versions are never reclaimed and 
autovacuum is disabled.

And positive value of this parameter specifies maximal time travel 
period in seconds.
As in case of disabled time travel, you can specify AS OF timestamp 
older than this period.
But there is no warranty that requested versions still exist.

-- 
Konstantin Knizhnik
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company