Subject: Re: Why are wait events not reported even though it reads/writes a
 timeline history file?
To: Masahiro Ikeda <ikedamsh@oss.nttdata.com>, pgsql-hackers@postgresql.org
References: <d11b0c910b63684424e06772eb844ab5@oss.nttdata.com>
From: Fujii Masao <masao.fujii@oss.nttdata.com>
Message-ID: <c2bed73d-2044-8ab1-075a-75ce0316a814@oss.nttdata.com>
Date: Mon, 27 Apr 2020 12:25:56 +0900
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On 2020/04/24 11:29, Masahiro Ikeda wrote:
> Hi,
> 
> There are two unexpected codes for me about wait events for timeline history file.
> Please let me know your thoughts whether if we need to change.
> 
> 
> 1. readTimeLineHistory() function in timeline.c
> 
> The readTimeLineHistory() reads a timeline history file,
> but it doesn't report “WAIT_EVENT_TIMELINE_HISTORY_READ".

Yeah, this sounds strange.

> In my understanding, sscanf() is blocking read.
> So, it's important to report a wait event.

Shouldn't the wait event be reported during fgets() rather than sscanf()?

> 2. writeTimeLineHistory() function in timeline.c
> 
> The writeTimeLineHistory() function may write a timeline history file twice,
> but it reports “WAIT_EVENT_TIMELINE_HISTORY_WRITE" only once.
> 
> It makes sense to report a wait event twice, because both of them use write().

Yes.

> I attached a patch to mention the code line number.
> 
> 
> I checked the commit log which "WAIT_EVENT_TIMELINE_HISTORY_READ" and
> "WAIT_EVENT_TIMELINE_HISTORY_WRITE" are committed and the discussion about it.
> But I can't find the reason.
> 
> Please give me your comments.
> If we need to change, I can make a patch to fix them.

Thanks! I agree to fix those issues.

> By the way, which is correct "timeline's history file" or "timeline history file"?
> The timeline.c has both. In my understanding, the latter is correct. If so, I will modify together.

Maybe both are correct?? I have no strong opinion about this.

Regards,

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