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Re: Avoiding rewrite in ALTER TABLE ALTER TYPE

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Noah Misch <noah(at)leadboat(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Avoiding rewrite in ALTER TABLE ALTER TYPE
Date: 2010-12-29 18:47:54
Message-ID: 721935F0-F996-4C11-850F-660BE77ED856@gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Dec 29, 2010, at 11:16 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> I really really dislike the notion of a "verification scan": it's
> basically work that is going to be useless if it fails.

I think it has potential in cases like text to xml.  In that case it'll either work or fail, with no possibility of requiring a do-over.  Scanning the whole table is a whole lot cheaper than rewriting it.  But I agree with your assessment of the "optimistic" verification scan case.

...Robert

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