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Re: Disabled features on Hot Standby

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Disabled features on Hot Standby
Date: 2012-01-13 17:18:40
Message-ID: CA+U5nMLk+7vzGfAieR1XiHhbc1eqDwOTPsZLg_0pSY+7Z77iiw@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Fri, Jan 13, 2012 at 5:08 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> Also, what happens if an all-visible bit gets set on the standby
> through some other mechanism - e.g. restored from an FPI or
> XLOG_HEAP_NEWPAGE?  I'm not sure whether we ever do an FPI of the
> visibility map page itself, but we certainly do it for the heap pages.
>  So it might be that this infrastructure would (somewhat bizarrely)
> trust the visibility map bits but not the PD_ALL_VISIBLE bits.  I'm
> hoping Heikki or Tom will comment on this thread, because I think
> there are a bunch of subtle issues here and that we could easily screw
> it up by trying to plow through the problem too hastily.

An FPI can't change the all visible flag. If it did, it would imply
that we'd skipped generation or replay of an XLOG_HEAP2_VISIBLE
record, or that we're doing crash recovery/inital startup and HS is
not yet enabled.

-- 
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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