| From: | Gokulakannan Somasundaram <gokul007(at)gmail(dot)com> |
|---|---|
| To: | Jeff Davis <pgsql(at)j-davis(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Greg Stark <stark(at)mit(dot)edu>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: An idle thought |
| Date: | 2010-03-19 06:19:27 |
| Message-ID: | 9362e74e1003182319t10d46c75x8cdac38ca2195e94@mail.gmail.com |
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| Thread: | |
| Lists: | pgsql-hackers |
> Surely the VM is already update-friendly. If you update a tuple in a
> page with the visibility bit set, the bit must be unset or you will get
> wrong results.
>
>
>
I was referring in the context of index only scans to skip visibility
checks. I doubt, whether the visibility map feature to skip visibility
checks at the heap can be created without any extra cost to updates/inserts.
When a data is compressed then there is more contention for the same block
and hence would likely affect DMLs. I hope that's what Tom was also
referring to, but not in the visibility map context.
Gokul.
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