Re: index prefetching

Andres Freund <andres@anarazel.de>

From: Andres Freund <andres@anarazel.de>

To: Peter Geoghegan <pg@bowt.ie>

Cc: Tomas Vondra <tomas@vondra.me>, 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: 2025-08-15T19:45:13Z

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 →

aio: io_uring: Trigger async processing for large IOs
- a9ee66881744 19 (unreleased) landed
read stream: Split decision about look ahead for AIO and combining
- 8ca147d582a5 19 (unreleased) landed
read_stream: Only increase read-ahead distance when waiting for IO
- f63ca3379025 19 (unreleased) landed
read_stream: Prevent distance from decaying too quickly
- 6e36930f9aaf 19 (unreleased) landed
Reduce ExecSeqScan* code size using pg_assume()
- b227b0bb4e03 19 (unreleased) cited
Fix rare bug in read_stream.c's split IO handling.
- b421223172a2 19 (unreleased) cited
Fix multiranges to behave more like dependent types.
- 3e8235ba4f9c 17.0 cited
Add EXPLAIN (MEMORY) to report planner memory consumption
- 5de890e3610d 17.0 cited
Optimize nbtree backward scan boundary cases.
- c9c0589fda0e 17.0 cited
Increment xactCompletionCount during subtransaction abort.
- 90c885cdab8b 14.0 cited
Add nbtree Valgrind buffer lock checks.
- 4a70f829d86c 14.0 cited
Add nbtree high key "continuescan" optimization.
- 29b64d1de7c7 12.0 cited
Reduce pinning and buffer content locking for btree scans.
- 2ed5b87f96d4 9.5.0 cited
Teach btree to handle ScalarArrayOpExpr quals natively.
- 9e8da0f75731 9.2.0 cited

Hi,

On 2025-08-15 15:42:10 -0400, Peter Geoghegan wrote:
> On Fri, Aug 15, 2025 at 3:38 PM Andres Freund <andres@anarazel.de> wrote:
> > I see absolutely no effect of the patch with shared_buffers=1GB and a
> > read-only scale 200 pgbench at 40 clients. What data sizes, shared buffers
> > etc. were you testing?
> 
> Just to be clear: you are testing with both the index prefetching
> patch and your patch together, right? Not just your own patch?

Correct.

> My shared_buffers is 16GB, with pgbench scale 300.

So there's actually no IO, given that a scale 300 is something like 4.7GB? In
that case my patch could really not make a difference, neither of the changed
branches would ever be reached?

Or were you testing the warmup phase, rather than the steady state?

Greetings,

Andres Freund