Re: Polyphase merge is obsolete

On 22/10/2020 14:48, Heikki Linnakangas wrote:
> On 11/09/2017 13:37, Tomas Vondra wrote:
>> I planned to do some benchmarking on this patch, but apparently the
>> patch no longer applies. Rebase please?
>
> Here's a rebase of this. Sorry to keep you waiting :-).

Here's an updated version that fixes one bug:

The CFBot was reporting a failure on the FreeBSD system [1]. It turned
out to be an out-of-memory issue caused by an underflow bug in the
calculation of the size of the tape read buffer size. With a small
work_mem size, the memory left for tape buffers was negative, and that
wrapped around to a very large number. I believe that was not caught by
the other systems, because the other ones had enough memory for the
incorrectly-sized buffers anyway. That was the case on my laptop at
least. It did cause a big slowdown in the 'tuplesort' regression test
though, which I hadn't noticed.

The fix for that bug is here as a separate patch for easier review, but
I'll squash it before committing.

[1] https://cirrus-ci.com/task/6699842091089920

- Heikki