Horton

Re: Moving relation extension locks out of heavyweight lock manager

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Masahiko Sawada <sawada.mshk@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2017-05-16T16:30:03Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Allow page lock to conflict among parallel group members.

  2. Allow relation extension lock to conflict among parallel group members.

  3. Add assert to ensure that page locks don't participate in deadlock cycle.

  4. Assert that we don't acquire a heavyweight lock on another object after

  5. Fix unsafe usage of strerror(errno) within ereport().

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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