On 2016/02/29 18:05, Thomas Munro wrote:
> On Mon, Feb 29, 2016 at 9:05 PM, Amit Langote wrote:
>> +         servers.  A transaction that is run with
>> <varname>causal_reads</> set
>> +         to <literal>on</> is guaranteed either to see the effects of all
>> +         completed transactions run on the primary with the setting on, or 
>> to
>> +         receive an error "standby is not available for causal reads".
>> "A transaction that is run" means "A transaction that is run on a
>> standby", right?
> Well, it could be any server, standby or primary.  Of course standbys
> are the interesting case since it it was already true that if you run
> two sequential transactions run on the primary, the second can see the
> effect of the first, but I like the idea of a general rule that
> applies anywhere, allowing you not to care which server it is.

I meant actually in context of that sentence only.

>> By the way, is there some discussion in our existing
>> documentation to refer to about causal consistency in single node case?  I
>> don't know maybe that will help ease into the new feature.  Grepping the
>> existing source tree doesn't reveal the term "causal", so maybe even a
>> single line in the patch mentioning "single node operation trivially
>> implies (or does it?) causal consistency" would help.  Thoughts?
> Hmm.  Where should such a thing go?  I probably haven't introduced the
> term well enough.  I thought for a moment about putting something
> here:
> http://www.postgresql.org/docs/devel/static/sql-commit.html
> "All changes made by the transaction become visible to others ..." --
> which others?  But I backed out, that succinct account of COMMIT is 20
> years old, and in any case visibility is tied to committing, not
> specifically to the COMMIT command.  But perhaps this patch really
> should include something there that refers back to the causal reads
> section.

I see.  I agree this is not exactly material for the COMMIT page.  Perhaps
somewhere under "Chapter 13. Concurrency Control" with cross-reference
to/from "25.5. Hot Standby".  Might be interesting to hear from others as


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