Horton

Re: adding wait_start column to pg_locks

torikoshia <torikoshia@oss.nttdata.com>

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From: torikoshia <torikoshia@oss.nttdata.com>
To: Fujii Masao <masao.fujii@oss.nttdata.com>
Cc: Ian Lawrence Barwick <barwick@gmail.com>, Robert Haas <robertmhaas@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2021-02-04T15:03:51Z
Lists: pgsql-hackers

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On 2021-02-03 11:23, Fujii Masao wrote:
>> 64-bit fetches are not atomic on some platforms. So spinlock is 
>> necessary when updating "waitStart" without holding the partition 
>> lock? Also GetLockStatusData() needs spinlock when reading 
>> "waitStart"?
> 
> Also it might be worth thinking to use 64-bit atomic operations like
> pg_atomic_read_u64(), for that.

Thanks for your suggestion and advice!

In the attached patch I used pg_atomic_read_u64() and 
pg_atomic_write_u64().

waitStart is TimestampTz i.e., int64, but it seems pg_atomic_read_xxx 
and pg_atomic_write_xxx only supports unsigned int, so I cast the type.

I may be using these functions not correctly, so if something is wrong, 
I would appreciate any comments.


About the documentation, since your suggestion seems better than v6, I 
used it as is.


Regards,

--
Atsushi Torikoshi

Commits

  1. Initialize atomic variable waitStart in PGPROC, at postmaster startup.

  2. Display the time when the process started waiting for the lock, in pg_locks, take 2

  3. Display the time when the process started waiting for the lock, in pg_locks.