Horton

Re: Deadlock in XLogInsert at AIX

Konstantin Knizhnik <k.knizhnik@postgrespro.ru>

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From: Konstantin Knizhnik <k.knizhnik@postgrespro.ru>
To: PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>, Bernd Helmle <mailings@oopsware.de>
Date: 2017-02-01T11:07:56Z
Lists: pgsql-hackers

Attachments

Attached please find my patch for XLC/AIX.
The most critical fix is adding __sync to pg_atomic_fetch_add_u32_impl.
The comment in this file says that:

       * __fetch_and_add() emits a leading "sync" and trailing "isync", 
thereby
       * providing sequential consistency.  This is undocumented.

But it is not true any more (I checked generated assembler code in 
debugger).
This is why I have added __sync() to this function. Now pgbench working 
normally.

Also there is mysterious disappearance of assembler section function 
with sync instruction from pg_atomic_compare_exchange_u32_impl.
I have fixed it by using __sync() built-in function instead.


Thanks to everybody who helped me to locate and fix this problem.

-- 

Konstantin Knizhnik
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company

Commits

  1. For all ppc compilers, implement compare_exchange and fetch_add with asm.

  2. For PowerPC instruction "addi", use constraint "b".

  3. For all ppc compilers, implement pg_atomic_fetch_add_ with inline asm.

  4. Replace xlc __fetch_and_add() with inline asm.

  5. Test pg_atomic_fetch_add_ with variable addend and 16-bit edge cases.