Re: delete then insert

Ron <ronljohnsonjr@xxxxxxxxx> · Fri, 17 Jan 2020 15:20:25 -0600



    On 1/17/20 2:59 PM, Ken Benson wrote:

    
        From: Ron
          <ronljohnsonjr@xxxxxxxxx>
          

          Sent: Friday, January 17, 2020 12:12 PM

          To: pgsql-admin@xxxxxxxxxxxxxxxxxxxx

          Subject: Re: delete then insert
         
        On 1/17/20 2:03
          PM, Ken Benson wrote:

          
          So – I THINK I
            know – that when a row is deleted from a table – the row is
            not actually removed from the table – but, merely marked as
            deleted, thus becoming a dead tuple.

            AUTOVACUUM – takes care of the process of removing these
            dead tuples.
           
          My question. If
            – an insert occurs to that same table before autovacuum
            comes along, does that inserted record use a dead tuple? Or
            – does the insert result in an actual added row?
        
        
          If there's an open transaction which is still looking at the
          now-deleted record, then over-writing that area of the file
          would be a Bad Thing.

          
        So – the
              answer is – NO – the dead tuple won’t be used until is has
              been reclaimed by vacuum – and that it doesn’t because it
              would be a bad thing, right?
      
    
    I don't know what happens if not other transaction is holding that
    "slot".

    
    -- 

      Angular momentum makes the world go 'round.