Horton

Re: index prefetching

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Tomas Vondra <tomas@vondra.me>
Cc: Andres Freund <andres@anarazel.de>, Thomas Munro <thomas.munro@gmail.com>, Nazir Bilal Yavuz <byavuz81@gmail.com>, Robert Haas <robertmhaas@gmail.com>, Melanie Plageman <melanieplageman@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Georgios <gkokolatos@protonmail.com>, Konstantin Knizhnik <knizhnik@garret.ru>, Dilip Kumar <dilipbalaut@gmail.com>
Date: 2025-08-15T02:12:35Z
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. aio: io_uring: Trigger async processing for large IOs

  2. read stream: Split decision about look ahead for AIO and combining

  3. read_stream: Only increase read-ahead distance when waiting for IO

  4. read_stream: Prevent distance from decaying too quickly

  5. Reduce ExecSeqScan* code size using pg_assume()

  6. Fix rare bug in read_stream.c's split IO handling.

  7. Fix multiranges to behave more like dependent types.

  8. Add EXPLAIN (MEMORY) to report planner memory consumption

  9. Optimize nbtree backward scan boundary cases.

  10. Increment xactCompletionCount during subtransaction abort.

  11. Add nbtree Valgrind buffer lock checks.

  12. Add nbtree high key "continuescan" optimization.

  13. Reduce pinning and buffer content locking for btree scans.

  14. Teach btree to handle ScalarArrayOpExpr quals natively.

On Thu, Aug 14, 2025 at 7:26 PM Tomas Vondra <tomas@vondra.me> wrote:
> Good. I admit I lost track of which the various regressions may affect
> existing plans, and which are specific to the prefetch patch.

As far as I know, we only have the following unambiguous performance
regressions (that clearly need to be fixed):

1. This issue.

2. There's about a 3% loss of throughput on pgbench SELECT. This isn't
surprising at all; it would be a near-miracle if this kind of
prototype quality code didn't at least have a small regression here
(it's not like we've even started to worry about small fixed costs for
simple selective queries just yet). This will need to be fixed, but
it's fairly far down the priority list right now.

I feel that we're still very much at the stage where it makes sense to
just fix the most prominent performance issue, and then reevaluate.
Repeating that process iteratively. It's quite likely that there are
more performance issues/bugs that we don't yet know about. IMV it
doesn't make sense to closely track individual queries that have only
been moderately regressed.

-- 
Peter Geoghegan