Re: Allocations in critical section (was Re: WAL format and API changes (9.5))

On 04/04/2014 04:56 PM, Tom Lane wrote:
> Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> writes:
>> Ok, I fixed the issues that the assertion fixed. I also committed a
>> patch to add the assertion itself; let's see if the buildfarm finds more
>> cases that violate the rule.
>
>> It ignores the checkpointer, because it's known to violate the rule,
>
> ... uh, isn't that a bug to be fixed?

Yes. One step a time ;-).

>> and
>> allocations in ErrorContext, which is used during error recovery, e.g if
>> you indeed PANIC while in a critical section for some other reason.
>
> Yeah, I realized we'd have to do something about elog's own allocations.
> Not sure if a blanket exemption for ErrorContext is the best way. I'd
> been thinking of having a way to turn off the complaint once processing
> of an elog(PANIC) has started.

Hmm. PANIC processing should avoid allocations too, except in
ErrorContext, because otherwise you might get an out-of-memory during
PANIC processing.

ErrorContext also covers elog(DEBUG2, ...). I presume we'll want to
ignore that too. Although I also tried without the exemption for
ErrorContext at first, and didn't get any failures from the regression
tests, so I guess we never do that in a critical section. I was a bit
surprised by that.

> BTW, I'm pretty sure you added some redundant assertions in mcxt.c.
> eg, palloc does not need its own copy.

palloc is copy-pasted from MemoryContextAlloc - it does need its own copy.

- Heikki