Re: Deadlock between backend and recovery may not be detected

On 2020/12/16 23:28, Drouvot, Bertrand wrote:
> Hi,
>
> On 12/16/20 2:36 PM, Victor Yegorov wrote:
>>
>> *CAUTION*: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
>>
>>
>> ср, 16 дек. 2020 г. в 13:49, Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com <mailto:masao(dot)fujii(at)oss(dot)nttdata(dot)com>>:
>>
>> After doing this procedure, you can see the startup process and backend
>> wait for the table lock each other, i.e., deadlock. But this deadlock remains
>> even after deadlock_timeout passes.
>>
>> This seems a bug to me.
>>
> +1
>
>>
>> > * Deadlocks involving the Startup process and an ordinary backend process
>> > * will be detected by the deadlock detector within the ordinary backend.
>>
>> The cause of this issue seems that ResolveRecoveryConflictWithLock() that
>> the startup process calls when recovery conflict on lock happens doesn't
>> take care of deadlock case at all. You can see this fact by reading the above
>> source code comment for ResolveRecoveryConflictWithLock().
>>
>> To fix this issue, I think that we should enable STANDBY_DEADLOCK_TIMEOUT
>> timer in ResolveRecoveryConflictWithLock() so that the startup process can
>> send PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK signal to the backend.
>> Then if PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK signal arrives,
>> the backend should check whether the deadlock actually happens or not.
>> Attached is the POC patch implimenting this.
>>
> good catch!
>
> I don't see any obvious reasons why the STANDBY_DEADLOCK_TIMEOUT shouldn't be set in ResolveRecoveryConflictWithLock() too (it is already set in ResolveRecoveryConflictWithBufferPin()).
>
> So + 1 to consider this as a bug and for the way the patch proposes to fix it.

Thanks Victor and Bertrand for agreeing!
Attached is the updated version of the patch.

Regards,

--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION