Re: [HACKERS] Moving relation extension locks out of heavyweight lock manager

On Sat, May 13, 2017 at 7:27 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
> On Fri, May 12, 2017 at 9:14 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Robert Haas <robertmhaas@gmail.com> writes:
>>> On Wed, May 10, 2017 at 8:39 PM, Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>>>> ... I'd like to propose to change relation
>>>> extension lock management so that it works using LWLock instead.
>>
>>> That's not a good idea because it'll make the code that executes while
>>> holding that lock noninterruptible.
>>
>> Is that really a problem?  We typically only hold it over one kernel call,
>> which ought to be noninterruptible anyway.
>
> During parallel bulk load operations, I think we hold it over multiple
> kernel calls.

We do.  Also, RelationGetNumberOfBlocks() is not necessarily only one
kernel call, no?  Nor is vm_extend.

Also, it's not just the backend doing the filesystem operation that's
non-interruptible, but also any waiters, right?

Maybe this isn't a big problem, but it does seem to be that it would
be better to avoid it if we can.

-- 
Robert Haas
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