Horton

Re: Connections hang indefinitely while taking a gin index's LWLock buffer_content lock(PG10.7)

Alexander Korotkov <a.korotkov@postgrespro.ru>

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From: Alexander Korotkov <a.korotkov@postgrespro.ru>
To: chenhj <chjischj@163.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-09-29T14:38:08Z
Lists: pgsql-hackers 
Hi!

Thank you for reporting.

On Sun, Sep 29, 2019 at 11:17 AM chenhj <chjischj@163.com> wrote:
> Does the locking order of autovacuum process(root->right->left) correct? While insert process lock gin buffer by order of bottom->top and left->right.
>
> 1. vacuum(root->right->left):

Starting from root seems OK for me, because vacuum blocks all
concurrent inserts before doing this.  But this needs to be properly
documented in readme.

Locking from right to left is clearly wrong.  It could deadlock with
concurrent ginStepRight(), which locks from left to right.  I expect
this happened in your case.  I'm going to reproduce this and fix.

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company

Commits

  1. Fix traversing to the deleted GIN page via downlink

  2. Revise GIN README

  3. Fix deadlock between ginDeletePage() and ginStepRight()