Re: WAL directory size calculation

Moreno Andreo <moreno.andreo@xxxxxxxxxx> · Thu, 28 Jul 2016 18:27:41 +0200



    Il 28/07/2016 15:33, David G. Johnston
      ha scritto:

    
        On Thu, Jul 28, 2016 at
            9:25 AM, Moreno Andreo <moreno.andreo@xxxxxxxxxx> wrote:

        
            I've
              read somewhere that the formula should be 16 MB * 3 *
              checkpoint_segment in size.

            
              [...]
               
            Using
              the above formula I have:

                  16 MB * 3 * 1 GB

              that leads to to ... uh .. 48000 TB?

            
              You seem
                to be mis-remembering the formula.
            
          
    The result is too big to be sane... so there *must* be something
    wrong

    
              checkpoiint_segments
                is a quantity (i.e., unit-less), not a size.  Saying its
                "1GB" makes no sense.
            
          
    Yes, my "1 GB" is related to max_wal_file_size, that from 9.5 came
    over checkpoint_segment.

    
              I'm
                also doubting you multiply it by 3 - add three to it
                maybe...
            
            
              Each
                segment takes 16MB.  The total space required is that
                times whatever maximum count of segments you expect to
                have.
            
          
    That's the variable. How many segments do I expect to have? (jumping
    from 9.1 (current) to 9.5 (new) documentation and having a bit of
    confusion in my head...)

    
              I'd
                suggest waiting for better responses on these lists
                ...[snip]...
            
          
    Got one, in fact. The statement to *absolutely* not use ramdisk with
    wal files resolved almost all of my doubts.

    
              David J.
              

    Thanks
    Moreno