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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: Noah Misch <noah(at)leadboat(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Disabled features on Hot Standby
Date: 2012-01-14 08:23:03
Message-ID: CA+U5nMJih0PgNXqZkf1R-6qbsdAC9Hgn6EYzoba=NeP2Ri+xVA@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Sat, Jan 14, 2012 at 5:42 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> Other than that, it seems like we might be converging on a workable
> solution: if hot_standby_feedback=off, disable index-only scans for
> snapshots taken during recovery; if hot_standby_feedback=on, generate
> recovery conflicts when a snapshot's xmin precedes the youngest xmin
> on a page marked all-visible, but allow the use of index-only scans,
> and allow sequential scans to trust PD_ALL_VISIBLE.  Off the top of my
> head, I don't see a hole in that logic...

Please use the logic described earlier. Using the existing mechanisms
and infrastructure is all we need here.

We want latestRemovedXid, not a new version of it via xmins. Keep
index-only scans enabled all the time and let conflicts be generated.
There are already mechanisms in place to handle conflicts, so avoiding
them another way is not required or desired.

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

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