Re: Proposal for Null Bitmap Optimization(for Trailing NULLs)

Added to TODO:

       * Consider not storing a NULL bitmap on disk if all the NULLs are
         trailing

         http://archives.postgresql.org/pgsql-hackers/2007-12/msg00624.php
         http://archives.postgresql.org/pgsql-patches/2007-12/msg00109.php

Tom's comments are:

       What this lacks is some performance testing to measure the cost of the
       extra tests in heap_form_tuple. If that can be shown to be negligible
       then it's probably worth doing .... though I don't like any part of the
       actually submitted patch ;-). All this should need is a bit more logic
       in heap_form_tuple and heap_formtuple.

---------------------------------------------------------------------------

Gokulakannan Somasundaram wrote:
> Hi,
>     Currently we check for the existence of NULL values in the tuple and we
> set the has_null flag. If the has_null flag is present, the tuple will be
> storing a null bitmap. What i propose is
>
> a) By modifying the functions, heap_form_tuple and heap_fill_tuple, we can
> check whether all the nulls are trailing nulls. If all the nulls are
> trailing nulls, then we will not set the has_null flag and we will not have
> the null bitmap with the tuple.
>
> b) While selecting the tuple, we will check whether the tuple offset equals
> / exceeds the length of the tuple and then mark the remaining attributes of
> the tuple as null. To be exact, we need to modify the slot_deform_tuple in
> order to achieve the same.
>
> This may not give huge performance benefits, but as you may know, it will
> help is reducing the disk footprint.
>
>
> Expecting your comments..
>
> --
> Thanks,
> Gokul.
> CertoSQL Project,
> Allied Solution Group.
> (www.alliedgroups.com)

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