Re: vary read_only in SPI calls? or poke at the on-entry snapshot?

From: Chapman Flack <chap(at)anastigmatix(dot)net>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: vary read_only in SPI calls? or poke at the on-entry snapshot?
Date: 2018-09-22 21:56:38
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On 09/20/18 00:44, Tom Lane wrote:
> Chapman Flack <chap(at)anastigmatix(dot)net> writes:
>> Would it be unprecedented / be unreasonable / break anything for the
>> install_jar function to simply force a CommandCounterIncrement
>> at the end of step 1 (after its temporary snapshot has been popped,
>> so the former/on-entry ActiveSnapshot gets the increment)?
> The risk you take there is changing the behavior of calling function(s).
>> 1. fiddle the loader to always pass read_only => false to SPI calls,
>> regardless of the volatility of the function it is loading for.
>> 2. leave the loader alone, and adjust install_jar (an infrequent
>> operation) to do something heretical with its on-entry snapshot.
> I suspect #1 is less likely to have bad side-effects. But I've not
> done any careful analysis.

Or, revisiting #2, what of install_jar first pushing a copied snapshot
(the current active one? a new one from GetTransactionSnapshot?) and
keeping that copy on the stack during both operations (loading the jar
and executing the deployment commands, with a CommandCounterIncrement
in between) and popping it before return?

Would that alleviate the concern of changing calling functions' behavior?


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