Horton

Re: BUG #19006: Assert(BufferIsPinned) in BufferGetBlockNumber() is triggered for forwarded buffer

Thomas Munro <thomas.munro@gmail.com>

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From: Thomas Munro <thomas.munro@gmail.com>
To: Xuneng Zhou <xunengzhou@gmail.com>
Cc: exclusion@gmail.com, pgsql-bugs@lists.postgresql.org, Michael Paquier <michael@paquier.xyz>, Tom Lane <tgl@sss.pgh.pa.us>
Date: 2025-08-08T15:06:53Z
Lists: pgsql-bugs

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

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On Fri, Aug 8, 2025 at 4:39 PM Xuneng Zhou <xunengzhou@gmail.com> wrote:
> Thanks a lot for the exceptionally detailed and insightful
> explanation—it’s far more comprehensive than I anticipated. It is
> excellent for unpacking the intricate interplay and state transitions
> between submodules, which is what makes this topic challenging to
> grasp. I’ll need some time to fully digest it, so I’m bookmarking this
> email for future reference. I’m also considering turning it into a
> blog post after studying—it’s the kind of deep, clear writing that
> could benefit more interested audiences.

Well, one benefit of trying to describe a complex system from the top
is that higher level stupidity can sometimes become clear...  I
realised that the queue wouldn't even need to be initialised or
cleared if StartReadBuffers() had an explicit in/out npinned argument
to transmit the count between calls along with the buffers, or
examined after each call.  This is a draft alternative fix that I am
studying that removes quite a lot of lines and fragility, though time
is not on my side so I might push the one-liner fix ahead of the
upcoming freeze and then see what to do about this.