Re: intermittent long "log file sync" waits

From: Chris Stephens <cstephens16_at_gmail.com>
Date: Tue, 28 Jan 2020 16:30:17 -0600
Message-ID: <CAEFL0sxN6tcpiTJLa8=5CWggEL-tV4T9DZdxjE=Sq7zRktvcVA_at_mail.gmail.com>



ok. i've had the following running since lunchtime and will let it run through the night in hopes that issue occurs again:

_at_snapper ash,stats,trace 10 999999 lgwr

I will run the following script as well:

#! /bin/bash

while [ 1 ]
do

    echo `date` >> /tmp/pstack.26552
    pstack 26552 >> /tmp/pstack.26552
    echo `date` >> /tmp/pstack.26556
    pstack 26556 >> /tmp/pstack.26556
    echo `date` >> /tmp/pstack.26560
    pstack 26560 >> /tmp/pstack.26560

    sleep 5
done

based off:

[oracle_at_lsst-oradb05 bin]$ ps -ef | egrep "lg.*lsst2db2"

oracle   26552     1  0 Jan17 ?        00:06:14 ora_lgwr_lsst2db2
oracle   26556     1  0 Jan17 ?        00:00:13 ora_lg00_lsst2db2
oracle   26560     1  0 Jan17 ?        00:00:12 ora_lg01_lsst2db2

All sessions for this workload are connecting to service w/ tracing enabled so we'll have trace data as well.

I will (hopefully) have updates in the morning.

On Tue, Jan 28, 2020 at 4:01 PM Noveljic Nenad <nenad.noveljic_at_vontobel.com> wrote:

> We need to find out what lg* are doing during long log file sync waits. As
> ash samples are entirely missing I propose to sample all lg* processes with
> pstack every second and store the information for the later analysis.
> Another useful information would be snapper stats output, say, also once
> per second and targeted to lg* from the same interval.
>
> This will generate lots of data but you can write a script to periodically
> delete it if there weren’t any incidents. You can easily detect them by
> counting log file sync samples.
>
> I’m really curious about this as usually long log file sync waits match
> some instrumented bg activity which is, apparently, not being the case here.
>
>
>
>
> *Von: *Noveljic Nenad <nenad.noveljic_at_vontobel.com>
> *Datum *Dienstag, 28. Jan. 2020, 10:17 PM
> *An: *cary.millsap_at_method-r.com <cary.millsap_at_method-r.com>, Stefan
> Koehler <contact_at_soocs.de>
> *Cc: *Chris Stephens <cstephens16_at_gmail.com>, oracle-l <
> Oracle-L_at_freelists.org>
> *Betreff: *RE: intermittent long "log file sync" waits
>
> In this case, though, there aren’t any ash entries for any of the lg*
> processes while the app sessions were waiting in log file sync for a long
> time.
>
>
>
>
>
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Received on Tue Jan 28 2020 - 23:30:17 CET

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