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From: Laurenz Albe <[email protected]>
To: James Pang <[email protected]>
To: Frits Hoogland <[email protected]>
Cc: [email protected]
Subject: Re: many sessions waiting DataFileRead and extend
Date: Thu, 26 Jun 2025 05:03:28 +0200
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAHgTRfff0+i4PV_9G-fAREdDcMi4J1StcCDG6NcJ=hGhT2-SvQ@mail.gmail.com>
References: <CAHgTRfdDkiX5bLRCYhrP18kFJjcvs1eHvL+jUtX1Ep-Y3=cFVg@mail.gmail.com>
	<[email protected]>
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	<CAHgTRfff0+i4PV_9G-fAREdDcMi4J1StcCDG6NcJ=hGhT2-SvQ@mail.gmail.com>

On Thu, 2025-06-26 at 10:32 +0800, James Pang wrote:
> thans for you suggestions, we have iowait from sar command too, copy here, checking with infra team not found abnormal IO activities either.  
> 02:00:01 PM  CPU    %usr   %nice    %sys %iowait    %irq   %soft  %steal  %guest  %gnice   %idle
> 02:00:03 PM  all   15.92    0.00   43.02    0.65    0.76    2.56    0.00    0.00    0.00   37.09

Crazy high system time.

If it is not transparent hugepages, the other suspect is fork().
Turn on "log_connections" for a minute or two and see if there are lots
of connections established.  That can easily use your CPU.

Other than that, I am out of guesses.

> Frits Hoogland <[email protected]> 於 2025年6月25日週三 下午10:27寫道：
> > > On 25 Jun 2025, at 07:59, Laurenz Albe <[email protected]> wrote:
> > > 
> > > Run "sar -P all 1" and see if "%iowait" is high.
> >
> > I would (strongly) advise against the use of iowait as an indicator.

I have heard that before, and I am sure you are right.

I grant that if it is low, it may just mean that the CPU is under load.
But if %iowait is high, my experience is that that indicates an I/O problem.

Yours,
Laurenz Albe

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