Horton

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

Robert Haas <robertmhaas@gmail.com>

View thread
From: Robert Haas <robertmhaas@gmail.com>
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Thomas Munro <thomas.munro@enterprisedb.com>, Amit Kapila <amit.kapila16@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2017-12-12T15:42:35Z
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 Mon, Dec 11, 2017 at 4:10 PM, Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> Thank you for updating the patch. Here is two minor comments.
>
> + * we acquire the same relation extension lock repeatedly.  nLocks is 0 is the
> + * number of times we've acquired that lock;
>
> Should it be "nLocks is the number of times we've acquired that lock:"?

Yes.

> +    /* Remember lock held by this backend */
> +    held_relextlock.relid = relid;
> +    held_relextlock.lock = relextlock;
> +    held_relextlock.nLocks = 1;
>
> We set held_relextlock.relid and held_relextlock.lock again. Can we remove them?

Yes.

Can you also try the experiment Andres mentions: "Measure two COPYs to
relations on different filesystems, reduce N_RELEXTLOCK_ENTS to 1, and
measure performance. Then increase the concurrency of the copies to
each relation."  We want to see whether and how much this regresses
performance in that case.  It simulates the case of a hash collision.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company