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Re: Largeobject Access Controls (r2460)

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Takahiro Itagaki <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, KaiGai Kohei <kaigai(at)ak(dot)jp(dot)nec(dot)com>, Jaime Casanova <jcasanov(at)systemguards(dot)com(dot)ec>, Greg Smith <greg(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Largeobject Access Controls (r2460)
Date: 2009-12-19 03:15:50
Message-ID: 603c8f070912181915y71877ea8gaf85eac4275d6f3c@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Fri, Dec 18, 2009 at 9:51 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> Part of what I'm confused about (and what I think should be documented
>> in a comment somewhere) is why we're using MVCC visibility in some
>> places but not others.  In particular, there seem to be some bits of
>> the comment that imply that we do this for read but not for write,
>> which seems really strange.  It may or may not actually be strange,
>> but I don't understand it.
>
> It is supposed to depend on whether you opened the blob for read only
> or for read write.  Please do not tell me that this patch broke that;
> because if it did it broke pg_dump.
>
> This behavior is documented at least here:
> http://www.postgresql.org/docs/8.4/static/lo-interfaces.html#AEN36338

Oh, I see.  Thanks for the pointer.  Having read that through, I can
now say that the comments in the patch seem to imply that it attempted
to preserve those semantics, but I can't swear that it did.  I will
take another look at it, but it might bear closer examination by
someone with more MVCC-fu than myself.

...Robert

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