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RE: [HACKERS] pg_dump/restore to convert BLOBs to LZTEXT (optional!)

From: Peter Mount <petermount(at)it(dot)maidstone(dot)gov(dot)uk>
To: "'Philip Warner'" <pjw(at)rhyme(dot)com(dot)au>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org, pgsql-general(at)postgresql(dot)org
Subject: RE: [HACKERS] pg_dump/restore to convert BLOBs to LZTEXT (optional!)
Date: 2000-08-04 06:55:52
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Lists: pgsql-generalpgsql-hackers
See below...

Peter Mount
Enterprise Support
Maidstone Borough Council
Any views stated are my own, and not those of Maidstone Borough Council

-----Original Message-----
From: Philip Warner [mailto:pjw(at)rhyme(dot)com(dot)au]
Sent: Friday, August 04, 2000 2:29 AM
To: Tom Lane
Cc: pgsql-hackers(at)postgreSQL(dot)org; pgsql-general(at)postgreSQL(dot)org
Subject: Re: [HACKERS] pg_dump/restore to convert BLOBs to LZTEXT

At 21:10 3/08/00 -0400, Tom Lane wrote:
>As well as break the semantics: if you have a multiply-referenced BLOB
>then you can update it through any reference and the changes are visible
>through all the references.  Not so after you convert the data into
>non-BLOB values.

That's what I meant. People *shouldn't* expect BLOB fields to be updated in
more than one table, but the implementation currently allow it (since BLOBs
are not implemented as fields).

Peter: I dissagree. There are dozens of instances where you would use a
single BLOB but refer to it in more than one table. If you have a 1Mb blob
refered to in 3 different tables, you don't want to store 3 instances of it.
Say you were implementing some form of DIP system (Document Image
Processing), then you only want one copy of the document stored, so that if
that document changes, then every instance is changed.

>I don't see that pg_dump can help meaningfully,
>and I'd just as soon resist feature bloat in pg_dump.

Fine. Thinking about it, even *if* it was implemented as a utility, I
suspect (for the reasons you outlined), conversion would be a multi-step
process. And a more useful utility would be one that converted an existing
database, rather than trying to everything in the 'restore'...

Peter: It might be useful to have the utility and put it under contrib. It
would then save people from reinventing the wheel.

Forget I even mentioned it.

Philip Warner                    |     __---_____
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and from   |/


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