Issue on restore / recover

From: flumbador(at)virgilio(dot)it
To: pgsql-admin(at)lists(dot)postgresql(dot)org
Subject: Issue on restore / recover
Date: 2017-12-29 15:21:26
Message-ID: 524817289.230206.1514560886805@mail.virgilio.it
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Hello

I've a question about postgresql restore / recover.

I have restored and recovered a Postgresql 9.4.9 from an hot backup. The backup is a filesystem copy taken while the Postgrsql is in backup mode (I mean between start and stop backup).

During the restore 3 files were missing; these three files belong to a table with high transaction workload, and for sure during the backup many transactions had modified this table and those missing files. What is surprising to me is that even if the files were missing the recover phase ended successfully. I expect an error (for example file not found) raised when postgresql try to apply the wal entries related to this table and those files. After the recover I find that these three file has been created during recover but when I try to query the table I get the error:

db4=# select count(*) from pgbench_accounts ;

ERROR: could not read block 1999996 in file "pg_tblspc/16471/PG_9.4_201409291/16474/16593.15": read only 0 of 8192 bytes

This error confirm that my database is corrupted! The question is: why during the recover phase Postgresql doesn't throw any errors? I think that is better to know immediately that we have restored our database from a corrupted backup rather then discover the issue after maybe a long time when a query is executed on the corrupted table.

Thanks in advance

Regards

Gabriele

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