Re: Postgresql crashdown and recovery failure

Ron <ronljohnsonjr@xxxxxxxxx> · Thu, 10 Jun 2021 22:41:17 -0500



    On 6/10/21 10:30 PM, xiebin (F) wrote:

    
        Hi,
         
        My database (Postgresql 12.5) server uses
            remote storage as data directory.
            
         
        I powered off the database server and started
            postgresql (same version) on another server, with same data.
            However it failed. I checked wal logs and found that the
            content around latest checkpoint is empty. (about 1700 zero
            bytes)
      
    
    [snip]

    
        From the output, I can see that data files,
            pg_control file and wal log are flushed to disk. And I
            noticed that pg_control file is flushed between 2 wal flush
            (as noted A,B,C).
         
        Here are my questions:
        
          1. 
              If power off
            occurs between B and C. Would it be possible that checkpoint
            was written to pg_control but not to wal log? And as a
            consequence, postgresql recovery would fail?
      
    
          2. 
              Is there any other
            reason causing this problem?
      
    
    Is your Postgresql instance configured to use fsync?

    
          3. 
              Is there any way
            to recover the data? I know pg_resetwal can reset wal log,
            then postgresql can start. But undoubtedly it could cause
            some data loss.
      
    
    -- 

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