Horton

Re: Non-reproducible AIO failure

Thomas Munro <thomas.munro@gmail.com>

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From: Thomas Munro <thomas.munro@gmail.com>
To: Nico Williams <nico@cryptonector.com>
Cc: Konstantin Knizhnik <knizhnik@garret.ru>, Alexander Lakhin <exclusion@gmail.com>, Andres Freund <andres@anarazel.de>, Daniel Gustafsson <daniel@yesql.se>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, rmt@lists.postgresql.org
Date: 2025-08-25T02:41:18Z
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: Stop using enum bitfields due to bad code generation

  2. amcheck: Fix posting tree checks in gin_index_check()

  3. aio: Add missing memory barrier when waiting for IO handle

On Mon, Aug 25, 2025 at 1:52 PM Thomas Munro <thomas.munro@gmail.com> wrote:
> >         struct { PgAioHandleState v:8; } state;
>
> This preserves type safety and compiles to strb two properties we
> want, but it seems to waste space (look at the offsets for the
> stores):
>
> a.out[0x1000005f8] <+140>: ldr    x8, [sp, #0x8]
> a.out[0x1000005fc] <+144>: strb   wzr, [x8, #0x8]
> a.out[0x100000600] <+148>: ldr    x8, [sp, #0x8]
> a.out[0x100000604] <+152>: strb   wzr, [x8, #0x4]

Sorry, I didn't make that very clear: that's open source clang 17
compiling assignment of zero to two neighbouring wrapped bitfields
with your trick.  Probably easier to look at the struct layout with
pahole or printf offsetof(...) or sizeof() to see that PgAioHandle
grows by 9 bytes of padding, something Andres obviously felt pretty
strongly about if he felt the need to summon bitfields...