| From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
|---|---|
| To: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Mike Blackwell <mike(dot)blackwell(at)rrd(dot)com> |
| Subject: | Re: Performance Improvement by reducing WAL for Update Operation |
| Date: | 2014-02-15 15:44:21 |
| Message-ID: | 20140215154421.GE19470@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
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
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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