Re: Performance Improvement by reducing WAL for Update Operation

On 2014-02-15 21:01:07 +0530, Amit Kapila wrote:
> >More importantly I don't think doing the compression on
> > this level is that interesting. I know Heikki argued for it, but I think
> > extending the bitmap that's computed for HOT to cover all columns and
> > doing this on a column level sounds much more sensible to me.
> 
> Previously we have tried to do at column boundaries, but the main problem
> turned out to be in worst cases where we spend time in extracting values
> from tuples based on column boundaries and later found that data is not
> compressible.

I think that hugely depends on how you implement it. I think you'd need
to have a loop traversing over the both tuples at the same time on the
level of heap_deform_tuple(). If you'd use the result to get rid of
HeapSatisfiesHOTandKeyUpdate() at the same time I am pretty sure you
wouldn't see very high overhead.

Greetings,

Andres Freund

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