Horton

Re: New strategies for freezing, advancing relfrozenxid early

John Naylor <john.naylor@enterprisedb.com>

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From: John Naylor <john.naylor@enterprisedb.com>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Jeff Davis <pgsql@j-davis.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Masahiko Sawada <sawada.mshk@gmail.com>
Date: 2022-09-15T07:09:44Z
Lists: pgsql-hackers 
On Wed, Sep 14, 2022 at 11:33 PM Peter Geoghegan <pg@bowt.ie> wrote:
>
> On Wed, Sep 14, 2022 at 3:18 AM John Naylor

> > Furthermore, it doesn't have to anticipate the maximum size, so there
> > is no up front calculation assuming max-tuples-per-page, so it
> > automatically uses less memory for less demanding tables.
>
> The final number of TIDs doesn't seem like the most interesting
> information that VM snapshots could provide us when it comes to
> building the dead_items TID data structure -- the *distribution* of
> TIDs across heap pages seems much more interesting. The "shape" can be
> known ahead of time, at least to some degree. It can help with
> compression, which will reduce cache misses.

My point here was simply that spilling to disk is an admission of
failure to utilize memory efficiently and thus shouldn't be a selling
point of VM snapshots. Other selling points could still be valid.

-- 
John Naylor
EDB: http://www.enterprisedb.com

Commits

  1. Revert "Add eager and lazy freezing strategies to VACUUM."

  2. Add eager and lazy freezing strategies to VACUUM.

  3. Refine the definition of page-level freezing.

  4. Avoid special XID snapshotConflictHorizon values.

  5. Add page-level freezing to VACUUM.

  6. Remove overzealous MultiXact freeze assertion.

  7. Refactor how VACUUM passes around its XID cutoffs.

  8. Deduplicate freeze plans in freeze WAL records.

  9. Set relfrozenxid to oldest extant XID seen by VACUUM.

  10. Only skip pages marked as clean in the visibility map, if the last 32

  11. Add vacuum_freeze_table_age GUC option, to control when VACUUM should