| From: | Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | "Andrey M(dot) Borodin" <x4mmm(at)yandex-team(dot)ru>, MBeena Emerson <mbeena(dot)emerson(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Andres Freund <andres(at)anarazel(dot)de>, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Stephen Frost <sfrost(at)snowman(dot)net> |
| Subject: | Re: recovering from "found xmin ... from before relfrozenxid ..." |
| Date: | 2020-08-03 09:05:38 |
| Message-ID: | CAE9k0Pm1bjfcHT7JWscGoWSc1MQbOEX8nKaJFb-Un0PSDGdEjw@mail.gmail.com |
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| Lists: | pgsql-hackers |
Hi Robert,
Thanks for the review.
I've gone through all your review comments and understood all of them
except this one:
You really cannot
> modify the buffer like this and then decide, oops, never mind, I think
> I won't mark it dirty or write WAL for the changes. If you do that,
> the buffer is still in memory, but it's now been modified. A
> subsequent operation that modifies it will start with the altered
> state you created here, quite possibly leading to WAL that cannot be
> correctly replayed on the standby. In other words, you've got to
> decide for certain whether you want to proceed with the operation
> *before* you enter the critical section.
>
Could you please explain this point once more in detail? I am not quite
able to understand under what circumstances a buffer would be modified, but
won't be marked as dirty or a WAL won't be written for it.
--
With Regards,
Ashutosh Sharma
EnterpriseDB:http://www.enterprisedb.com
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