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Re: pg_upgrade failing for 200+ million Large Objects

Andrew Dunstan <andrew@dunslane.net>

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From: Andrew Dunstan <andrew@dunslane.net>
To: Jan Wieck <jan@wi3ck.info>, Tom Lane <tgl@sss.pgh.pa.us>
Cc: Magnus Hagander <magnus@hagander.net>, Robins Tharakan <tharakan@gmail.com>, Peter Eisentraut <peter.eisentraut@enterprisedb.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2021-03-21T11:47:12Z
Lists: pgsql-hackers 
On 3/20/21 12:55 PM, Jan Wieck wrote:
> On 3/20/21 11:23 AM, Tom Lane wrote:
>> Jan Wieck <jan@wi3ck.info> writes:
>>> All that aside, the entire approach doesn't scale.
>>
>> Yeah, agreed.  When we gave large objects individual ownership and ACL
>> info, it was argued that pg_dump could afford to treat each one as a
>> separate TOC entry because "you wouldn't have that many of them, if
>> they're large".  The limits of that approach were obvious even at the
>> time, and I think now we're starting to see people for whom it really
>> doesn't work.
>
> It actually looks more like some users have millions of "small
> objects". I am still wondering where that is coming from and why they
> are abusing LOs in that way, but that is more out of curiosity. Fact
> is that they are out there and that they cannot upgrade from their 9.5
> databases, which are now past EOL.
>

One possible (probable?) source is the JDBC driver, which currently
treats all Blobs (and Clobs, for that matter) as LOs. I'm working on
improving that some: <https://github.com/pgjdbc/pgjdbc/pull/2093>


cheers


andrew


--
Andrew Dunstan
EDB: https://www.enterprisedb.com

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Count individual SQL commands in pg_restore's --transaction-size mode.

  2. Reduce number of commands dumpTableSchema emits for binary upgrade.

  3. Invent --transaction-size option for pg_restore.

  4. Rearrange pg_dump's handling of large objects for better efficiency.

  5. Add temporal PRIMARY KEY and UNIQUE constraints

  6. Fix typo and case in messages