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Re: Largeobject Access Controls (r2460)

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: KaiGai Kohei <kaigai(at)ak(dot)jp(dot)nec(dot)com>
Cc: Takahiro Itagaki <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, 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: 2009-12-18 14:00:47
Message-ID: 603c8f070912180600r2ced8b4bv3e1f975e58557d74@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
2009/12/18 KaiGai Kohei <kaigai(at)ak(dot)jp(dot)nec(dot)com>:
> (2009/12/18 15:48), Takahiro Itagaki wrote:
>>
>> Robert Haas<robertmhaas(at)gmail(dot)com>  wrote:
>>
>>> In both cases, I'm lost.  Help?
>>
>> They might be contrasted with the comments for myLargeObjectExists.
>> Since we use MVCC visibility in loread(), metadata for large object
>> also should be visible in MVCC rule.
>>
>> If I understand them, they say:
>>    * pg_largeobject_aclmask_snapshot requires a snapshot which will be
>>      used in loread().
>>    * Don't use LargeObjectExists if you need MVCC visibility.
>
> Yes, correct.
>
>>> In acldefault(), there is this comment:
>>>    /* Grant SELECT,UPDATE by default, for now */
>>> This doesn't seem to match what the code is doing, so I think we
>>> should remove it.
>>
>> Ah, ACL_NO_RIGHTS is the default.
>
> Oops, it reflects very early phase design, but fixed later.
>
>>> I also notice that dumpBlobComments() is now misnamed, but it seems
>>> we've chosen to add a comment mentioning that fact rather than fixing it.
>>
>> Hmmm, now it dumps not only comments but also ownership of large objects.
>> Should we rename it dumpBlobMetadata() or so?
>
> It seems to me quite natural.
>
> The attached patch fixes them.

I think we might want to go with dumpBlobProperties(), because
dumpBlobMetadata() might lead you to think that all of the properties
being dumped are stored in pg_largeobject_metadata, which is not the
case.

I do also wonder why we are calling these blobs in this code rather
than large objects, but that problem predates this patch and I think
we might as well leave it alone for now.

...Robert

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