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

From Jialun Zhang
Subject If crashes during VACUUM, will it recover from a checkpoint that is before the forzen transaction ID of VACUUM?
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Msg-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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