Re: Proposal for Signal Detection Refactoring - Mailing list pgsql-hackers
| From | Chris Travers |
|---|---|
| Subject | Re: Proposal for Signal Detection Refactoring |
| Date | |
| Msg-id | CAN-RpxB_MMUJhbOocDVOYsLZV4729xHpZkB6e+tqF7LLNCE1_Q@mail.gmail.com Whole thread Raw |
| In response to | Re: Proposal for Signal Detection Refactoring (Michael Paquier <michael@paquier.xyz>) |
| Responses |
Re: Proposal for Signal Detection Refactoring
|
| List | pgsql-hackers |
First, thanks for taking the time to write this. Its very helpful. Additional thoughts inline.
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On Mon, Sep 24, 2018 at 2:12 AM Michael Paquier <michael@paquier.xyz> wrote:
On Fri, Sep 21, 2018 at 12:35:46PM +0200, Chris Travers wrote:
> I understand how lock levels don't fit a simple hierarchy but at least
> when it comes to what is going to be aborted on a signal, I am having
> trouble understanding the problem here.
It may be possible to come with a clear hierarchy with the current
interruption types in place. Still I am not sure that the definition
you put behind is completely correct, and I think that we need to
question as well the value of putting such restrictions for future
interruption types because they would need to fit into it.
The future-safety issue is a really good one and it's one reason I kept the infinite loop patch as semantically consistent with the API as I could at the cost of some complexity.
I have another area where I think a patch would be more valuable anyway in terms of refactoring.
That's quite
a heavy constraint to live with. There is such logic with wal_level for
example, which is something I am not completely happy with either...
But this one is a story for another time, and another thread.
From a cleanup perspective a concentric circles approach seems like it is correct to me (which would correspond to a hierarchy of interrupts) but I can see that assuming that all pending interrupts would be checked solely for cleanup reasons might be a bad assumption on my part.
Regarding your patch, it seems to me that it does not improve
readability as I mentioned up-thread because you lose sight of what can
be interrupted in a given code path, which is what the current code
shows actually nicely.
So I guess there are two fundamental questions here.
1. Do we want to move away from checking global flags like this directly? I think we do because it makes future changes possibly harder and more complex since there is no encapsulation of logic. But I don't see a point in putting effort into that without consensus.
There could be value in refactoring things so as all the *Pending flags
of miscadmin.h get stored into one single volatile sig_atomic_t which
uses bit-wise markers, as that's at least 4 bytes because that's stored
as an int for most platforms and can be performed as an atomic operation
safely across signals (If my memory is right;) ). And this leaves a lot
of room for future flags.
Yeah I will look into this.
Thanks again for taking the time to go over the concerns in detail. It really helps.
Best Wishes,
Chris Travers
--
Michael
Best Regards,
Chris Travers
Head of Database
Saarbrücker Straße 37a, 10405 Berlin
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