| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> |
| Cc: | Amul Sul <sulamul(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Andrew Dunstan <andrew(at)dunslane(dot)net>, "Bossart, Nathan" <bossartn(at)amazon(dot)com>, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, "masao(dot)fujii(at)oss(dot)nttdata(dot)com" <masao(dot)fujii(at)oss(dot)nttdata(dot)com>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org>, "mengjuan(dot)cmj(at)alibaba-inc(dot)com" <mengjuan(dot)cmj(at)alibaba-inc(dot)com>, "Jakub(dot)Wartak(at)tomtom(dot)com" <Jakub(dot)Wartak(at)tomtom(dot)com>, Ryo Matsumura <matsumura(dot)ryo(at)fujitsu(dot)com> |
| Subject: | Re: prevent immature WAL streaming |
| Date: | 2021-11-25 20:12:14 |
| Message-ID: | 318012.1637871134@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> writes:
> On 2021-Nov-25, Tom Lane wrote:
>> Really? AFAICS the WAL record contains the correct value, or at least
>> we should define that one as being correct, for precisely this reason.
> I don't know what is the correct value for a record that comes exactly
> after the page header. But here's a patch that fixes the problem; and
> if a standby replays WAL written by an unpatched primary, it will be
> able to read past instead of dying of FATAL.
Meh ... but given the simplicity of the write-side fix, maybe changing
it is appropriate.
However, this seems too forgiving:
+ if (xlrec->overwritten_lsn != state->overwrittenRecPtr &&
+ xlrec->overwritten_lsn - SizeOfXLogShortPHD != state->overwrittenRecPtr &&
+ xlrec->overwritten_lsn - SizeOfXLogLongPHD != state->overwrittenRecPtr)
The latter two cases should only be accepted if overwrittenRecPtr is
exactly at a page boundary.
regards, tom lane
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