Re: WAL directory size calculation - Mailing list pgsql-general

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

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        <div class="gmail_default"
          style="font-family:arial,helvetica,sans-serif"><span
            style="font-family:arial,sans-serif">On Thu, Jul 28, 2016 at
            9:25 AM, Moreno Andreo <span dir="ltr"
            style="font-family:arial,sans-serif"><<a
              moz-do-not-send="true"
              href="mailto:moreno.andreo@evolu-s.it" target="_blank">moreno.andreo@evolu-s.it><span
            style="font-family:arial,sans-serif"> wrote:



            <blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">I've
              read somewhere that the formula should be 16 MB * 3 *
              checkpoint_segment in size.


              <div class="gmail_default"
                style="font-family:arial,helvetica,sans-serif;display:inline">​[...]​
               
            <blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">Using
              the above formula I have:
                  16 MB * 3 * 1 GB
              that leads to to ... uh .. 48000 TB?




              <div class="gmail_default"
                style="font-family:arial,helvetica,sans-serif">​You seem
                to be mis-remembering the formula.​





    The result is too big to be sane... so there *must* be something
    wrong
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              <div class="gmail_default"
                style="font-family:arial,helvetica,sans-serif;display:inline">​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.
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              <div class="gmail_default"
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              <div class="gmail_default"
                style="font-family:arial,helvetica,sans-serif;display:inline">​I'm
                also doubting you multiply it by 3 - add three to it
                maybe...


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              <div class="gmail_default"
                style="font-family:arial,helvetica,sans-serif">​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...)

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              <div class="gmail_default"
                style="font-family:arial,helvetica,sans-serif">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.

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              <div class="gmail_default"
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              <div class="gmail_default"
                style="font-family:arial,helvetica,sans-serif">David J.






    Thanks
    Moreno