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Re: Upgrading rant.

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Hannu Krosing <hannu(at)tm(dot)ee>
Cc: mlw <pgsql(at)mohawksoft(dot)com>, Lamar Owen <lamar(dot)owen(at)wgcr(dot)org>,pgsql-hackers(at)postgresql(dot)org
Subject: Re: Upgrading rant.
Date: 2003-01-03 20:37:56
Message-ID: 11163.1041626276@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Hannu Krosing <hannu(at)tm(dot)ee> writes:
> I don't think the main issues are with file _formats_ but rather with
> system file structures - AFAIK it is a fundamental design decision
> (arguably a design flaw ;( ) that we use system tables straight from
> page cache via C structure pointers,

The system tables are not the problem.  pg_upgrade has shown how we
can have cross-version upgrades no matter how much the system catalogs
change (a good thing too, because we cannot freeze the system catalog
layout without bringing development to a standstill).  A schema-only
dump and restore is cheap enough that there's no real reason to look
for any other solution.

Changes in the on-disk representation of user tables would be harder to
deal with, but they are also much rarer (AFAIR we've only done that
twice: WAL required additions to page and tuple headers, and then there
were Manfred's space-saving changes in 7.3).  And as of 7.3 there is a
version field in page headers, which would in theory allow for a
page-at-a-time update process to work.

There isn't any fundamental reason why we cannot have a pg_upgrade
utility; claiming that there is something wrong with how we handle
catalog changes misses the point.  The point is that *someone would
have to do the work*.  Unless someone wants to step up and volunteer,
there's little value in discussing it.

			regards, tom lane

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