From: | Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> |
---|---|
To: | nathandbossart(at)gmail(dot)com |
Cc: | zhjwpku(at)gmail(dot)com, xu(dot)xw2008(at)163(dot)com, pgsql-bugs(at)lists(dot)postgresql(dot)org |
Subject: | Re: BUG #17903: There is a bug in the KeepLogSeg() |
Date: | 2023-04-21 01:42:31 |
Message-ID: | 20230421.104231.1594652765237022266.horikyota.ntt@gmail.com |
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Lists: | pgsql-bugs |
At Thu, 20 Apr 2023 15:02:42 -0700, Nathan Bossart <nathandbossart(at)gmail(dot)com> wrote in
> I wonder if it'd be better to instead change
>
> if (currSegNo - segno > slot_keep_segs)
> to
> if (currSegNo > segno + slot_keep_segs)
>
> and
>
> if (currSegNo - segno < keep_segs)
> to
> if (currSegNo < segNo + keep_segs)
>
> If segno > currSegNo, the first conditional would be false as expected, and
> the second would be true as expected. We could also use
> pg_sub_u64_overflow() to detect underflow, but that might be excessive in
> this case.
From what I understand, the XLogSegNo calculations are designed
without considering the actual value range. Basically, it assumes that
(XLogSegNo + <any positive int>) can overflow. If we take the actual
value range into account, we can make that change.
The choice lies on whether we assume the actual value range or not.
regards.
--
Kyotaro Horiguchi
NTT Open Source Software Center
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