If crashes during VACUUM, will it recover from a checkpoint that is before the forzen transaction ID of VACUUM?

From: Jialun Zhang <reatank(at)gmail(dot)com>
To: pgsql-general(at)lists(dot)postgresql(dot)org
Subject: If crashes during VACUUM, will it recover from a checkpoint that is before the forzen transaction ID of VACUUM?
Date: 2020-07-02 03:16:56
Message-ID: CAMFL+Jj8c6RY4_HfmHDJN4x1E3O=KwYPWUuRex4hTt++Be45Ag@mail.gmail.com
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Hello All,

When VACUUM starts, it will calculate a frozen transaction ID and freeze
all tuples older than it. Will this frozen TXID younger than the latest
checkpoint?

If this is the case, then when the system crashes after VACUUM has deleted
some dead tuples and the system recovers from this checkpoint, these tuples
will be available to some transactions again during the replaying of WAL.

I am new to Postgres, hope my understanding is not too wrong.

Thanks,
Reatank

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