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

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] Moving relation extension locks out of heavyweight lock manager
Date: 2017-12-11 20:15:50
Message-ID: CA+TgmoZkTfTvuEJr-SeuDqiPH4MmvRdpRGO=uT+qNRc5_qxTGg@mail.gmail.com
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On Sun, Dec 10, 2017 at 11:51 PM, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> Attached updated version patch. Please review it.

I went over this today; please find attached an updated version which
I propose to commit.

Changes:

- Various formatting fixes, including running pgindent.

- Various comment updates.

- Make RELEXT_WAIT_COUNT_MASK equal RELEXT_LOCK_BIT - 1 rather than
some unnecessarily smaller number.

- In InitRelExtLocks, don't bother using mul_size; we already know it
won't overflow, because we did the same thing in RelExtLockShmemSize.

- When we run into an error trying to release a lock, log it as a
WARNING and don't mark it as translatable. Follows lock.c. An ERROR
here probably just recurses infinitely.

- Don't bother passing OID to RelExtLockRelease.

- Reorder functions a bit for (IMHO) better clarity.

- Make UnlockRelationForExtension just use a single message for both
failure modes. They are closely-enough related that I think that's
fine.

- Make WaitForRelationExtensionLockToBeFree complain if we already
hold an extension lock.

- In RelExtLockCleanup, clear held_relextlock.waiting. This would've
made for a nasty bug.

- Also in that function, assert that we don't hold both a lock and a wait count.

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

Attachment Content-Type Size
extension-lock-v12.patch application/octet-stream 43.8 KB

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