Re: Inefficiency in parallel pg_restore with many tables

Nathan Bossart <nathandbossart@gmail.com>

From: Nathan Bossart <nathandbossart@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Alvaro Herrera <alvherre@alvh.no-ip.org>, Andrew Dunstan <andrew@dunslane.net>, pgsql-hackers@lists.postgresql.org
Date: 2023-09-01T20:52:48Z
Lists: pgsql-hackers
On Fri, Sep 01, 2023 at 04:00:44PM -0400, Robert Haas wrote:
> In hindsight, I think that making binaryheap depend on Datum was a bad
> idea. I think that was my idea, and I think it wasn't very smart.
> Considering that people have coded to that decision up until now, it
> might not be too easy to change at this point. But in principle I
> guess you'd want to be able to make a heap out of any C data type,
> rather than just Datum, or just Datum in the backend and just void *
> in the frontend.

Yeah, something similar to simplehash for binary heaps could be nice.  That
being said, I don't know if there's a strong reason to specialize the
implementation for a given C data type in most cases.  I suspect many
callers are just fine with dealing with pointers (e.g., I wouldn't store an
entire TocEntry in the array), and smaller types like integers are already
stored directly in the array thanks to the use of Datum.  However, it
_would_ allow us to abandon this frontend/backend void */Datum kludge,
which is something.

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com



Commits

  1. Remove open-coded binary heap in pg_dump_sort.c.

  2. Convert pg_restore's ready_list to a priority queue.

  3. Add function for removing arbitrary nodes in binaryheap.

  4. Make binaryheap available to frontend code.