Horton

Re: Add 64-bit XIDs into PostgreSQL 15

Justin Pryzby <pryzby@telsasoft.com>

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From: Justin Pryzby <pryzby@telsasoft.com>
To: "Finnerty, Jim" <jfinnert@amazon.com>
Cc: Alexander Korotkov <aekorotkov@gmail.com>, Maxim Orlov <orlovmg@gmail.com>, pgsql-hackers@postgresql.org
Date: 2022-01-07T16:09:21Z
Lists: pgsql-hackers

Commits

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

  1. Add SLRU tests for 64-bit page case

  2. Make use FullTransactionId in 2PC filenames

  3. Use larger segment file names for pg_notify

  4. Index SLRUs by 64-bit integers rather than by 32-bit integers

On Fri, Jan 07, 2022 at 03:53:51PM +0000, Finnerty, Jim wrote:
> I'd still like a plan to retire the "double xmax" representation eventually.  Previously I suggested that this could be done as a post-process, before upgrade is complete, but that could potentially make upgrade very slow. 
> 
> Another way to retire the "double xmax" representation eventually could be to disallow "double xmax" pages in subsequent major version upgrades (e.g. to PG16, if "double xmax" pages are introduced in PG15).  This gives the luxury of time after a fast upgrade to convert all pages to contain the epochs, while still providing a path to more maintainable code in the future.

Yes, but how are you planning to rewrite it?  Is vacuum enough?
I suppose it'd need FREEZE + DISABLE_PAGE_SKIPPING ?

This would preclude upgrading "across" v15.  Maybe that'd be okay, but it'd be
a new and atypical restriction.

How would you enforce that it'd been run on v15 before upgrading to pg16 ?

You'd need to track whether vacuum had completed the necessary steps in pg15.
I don't think it'd be okay to make pg_upgrade --check to read every tuple.

The "keeping track" part is what reminds me of the online checksum patch.
It'd be ideal if there were a generic solution to this kind of task, or at
least a "model" process to follow.

-- 
Justin