Thread

1. Re: BUG: ReadStream look-ahead exhausts local buffers when effective_io_concurrency>=64

   Feike Steenbergen <feikesteenbergen@gmail.com> — 2026-05-06T12:24:38Z

   Hi, all,
   
   > On Tue, 10 Mar 2026 at 23:22, Induja Sreekanthan <indujas@google.com>
   wrote:
   > >
   > > Hi,
   > >
   > > I found an issue where Postgres (with effective_io_concurrency of 64 or
   higher) runs out of local buffers during a sequential scan on a temporary
   table with TOAST data.
   > >
   
   Just to confirm, I have a production db (20TB, high concurrency, lot's of
   updates/merges) that
   is a heavy user of temp tables running into this as well with
   io_method='io_uring'.
   
   This started after having upgraded PostgreSQL 18 (from 17).
   For now, the problem disappears again when switching to io_method='worker'
   
   Thank you for providing the patches,
   
   kind regards,
   
   Feike Steenbergen
   

2. Re: BUG: ReadStream look-ahead exhausts local buffers when effective_io_concurrency>=64

   Feike Steenbergen <feikesteenbergen@gmail.com> — 2026-05-06T12:47:46Z

   On Wed, 6 May 2026 at 14:24, Feike Steenbergen <feikesteenbergen@gmail.com>
   wrote:
   > For now, the problem disappears again when switching to io_method='worker'
   
   I spoke too soon it seems. It happens less frequently, but we do still have
   the issue even with io_method='worker'.
   Reverting to io_method='sync' as I would expect that will solve the issue.
   
   Feike