Re: Polyphase merge is obsolete

Heikki Linnakangas <hlinnaka@iki.fi>

From: Heikki Linnakangas <hlinnaka@iki.fi>
To: Jaime Casanova <jcasanov@systemguards.com.ec>
Cc: vignesh C <vignesh21@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>, Peter Geoghegan <pg@bowt.ie>, Tomas Vondra <tomas.vondra@2ndquadrant.com>
Date: 2021-09-15T21:35:16Z
Lists: pgsql-hackers

Attachments

On 16/09/2021 00:12, Jaime Casanova wrote:
> On Sat, Sep 11, 2021 at 01:35:27AM -0500, Jaime Casanova wrote:
>> On Wed, Jul 14, 2021 at 06:04:14PM +0300, Heikki Linnakangas wrote:
>>> On 14/07/2021 15:12, vignesh C wrote:
>>>> On Sat, Jan 23, 2021 at 3:49 AM Heikki Linnakangas <hlinnaka@iki.fi> wrote:
>>>>> 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.
>>>>
>>>> The patch does not apply on Head anymore, could you rebase and post a
>>>> patch. I'm changing the status to "Waiting for Author".
>>>
>>> Here's a rebased version. I also squashed that little bug fix from previous
>>> patch set.
>>>
>>
>> Hi,
>>
>> This patch does not apply, can you submit a rebased version?
> 
> BTW, I'm marking this one as "waiting on author"

Thanks, here's another rebase.

- Heikki

Commits

  1. Fix and clarify function comment on LogicalTapeSetCreate.

  2. Refactor LogicalTapeSet/LogicalTape interface.

  3. Replace polyphase merge algorithm with a simple balanced k-way merge.

  4. logtape.c: do not preallocate for tapes when sorting