Re: Index-only scans and non-MVCC snapshots

On 2014-06-26 22:47:47 -0600, Ryan Johnson wrote:
> Hi,
>
> As part of a research project, I'm trying to change Read Committed isolation
> to use HeapTupleSatisfiesNow rather than acquiring a new snapshot at every
> command [1]. Things appear to have gone reasonably well so far, except
> certain queries fail with "ERROR: non-MVCC snapshots are not supported in
> index-only scans."

You're aware that unless you employ additional locking you can simply
miss individual rows or see them several times because of concurrent
updates?
The reason it has worked (< 9.4) for system catalogs is that updates of
rows were only performed while objects were locked access exclusively -
that's the reason why some places in the code use inplace updates btw...

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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