RE: wrong start_time and start_date in v$transaction

From: Noveljic Nenad <nenad.noveljic_at_vontobel.com>
Date: Tue, 8 Sep 2020 12:23:51 +0000
Message-ID: <27309_1599567853_5F5777ED_27309_5121_1_a1baeba1bab6472ea93ff5032f7e3790_at_vontobel.com>



Hi Sayan,

The “drift” message is due to NTP correction. That might happen.

In my case nanosleep system call doesn’t come back at all (the afore mentioned nanosleep kernel function is just the wrapper to the syscall)

truss -f -p 14583
14583: nanosleep(0x7FFFBFFFC7D0, 0x7FFFBFFFC7E0) (sleeping...)

The parameters are correct (0s and 300000000ns):

(gdb) x/128d 0x7FFFBFFFC7D0
(gdb) print *(uint64_t)0x7FFFBFFFC7D0
$1 = 0
(gdb) print *(uint64_t)0x7FFFBFFFC7E0
$2 = 30000000

I don’t know if there are any tools available to overhaul the syscall itself.

There were some issues with the TimeKeeper 35 minutes prior to when the problem started:

Sep  5 22:30:09 svglb10a TimeKeeper[1938]: [ID 702911 daemon.alert] 1599345009.535993715: Time source change NTP(IP1:DTS) -> NTP(IP2:DTS) (source 5 -> source 6)
Sep  5 22:30:36 svglb10a TimeKeeper[1938]: [ID 702911 daemon.alert] 1599345036.811865464: Time source change NTP(IP1:DTS) -> NTP(IP2:DTS) (source 5 -> source 6)
Sep  5 22:45:42 svglb10a TimeKeeper[1938]: [ID 702911 daemon.alert] 1599345942.054030764: Time source change NTP(IP2:DTS) -> NTP(IP1:DTS) (source 6 -> source 5)
Sep  5 22:46:08 svglb10a TimeKeeper[1938]: [ID 702911 daemon.alert] 1599345968.982623273: Time source change NTP(IP2:DTS) -> NTP(IP1:DTS) (source 6 -> source 5)

No other warnings - neither in diag nor in /var/adm/messages.

Currently checking with sysadmins.

Best regards,

Nenad

http://nenadnoveljic.com/blog/

From: Sayan Malakshinov <xt.and.r_at_gmail.com> Sent: Dienstag, 8. September 2020 13:52 To: Noveljic Nenad <nenad.noveljic_at_vontobel.com> Cc: Frank Gordon <frankagordon_at_gmail.com>; mvelikikh_at_gmail.com; Jonathan Lewis <jlewisoracle_at_gmail.com>; Andy Sayer <andysayer_at_gmail.com>; Clay Jackson (cjackson) <Clay.Jackson_at_quest.com>; ORACLE-L (oracle-l_at_freelists.org) <oracle-l_at_freelists.org> Subject: Re: wrong start_time and start_date in v$transaction

Hi Nenad,

Btw, I've just recalled that we saw twice this year how oracle suddenly stopped without any error messages or core dumps and the last record was something like 'Warning: VKTM detected a time drift'. I'm not sure was it the root cause of it, but just FYI

On Tue, Sep 8, 2020 at 2:33 PM Noveljic Nenad <nenad.noveljic_at_vontobel.com<mailto:nenad.noveljic_at_vontobel.com>> wrote: The dedicated process doesn’t call the timestamp function itself. It rather reads the current value from an address location which is continuously updated by the VKTM. This is probably an optimization, because the real time timestamp function is expensive.

In my case, vktm hangs and it doesn’t update the location holding the current Epoch time. The stale timestamp gets then copied in each transaction entry.

Since vktm hangs in nanosleep OS kernel call, it might be an OS issue:

pstack 14583
14583: ora_vktm_ATRM2
00007fff93c76eba nanosleep (7fffbfffc7d0, 7fffbfffc7e0) 00000000072f3e9a sltrusleep () + 6a
000000000758b994 kstmrmtickcntkeeper () + 5a4 000000000758b1f4 kstmmainvktm () + 194

00000000072f5869 ksbrdp () + 9a9
0000000006efc489 opirip () + 2b9
0000000006118950 opidrv () + 160

0000000006118767 sou2o () + 97
0000000006118534 opimai_real () + a4
000000000611808b ssthrdmain () + 26b
0000000006117df9 main () + a9
0000000007771e34 ???????? ()

Best regards,

Nenad

https://nenadnoveljic.com/blog



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Best regards,
Sayan Malakshinov
Oracle performance tuning engineer
Oracle ACE Associate
http://orasql.org

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Received on Tue Sep 08 2020 - 14:23:51 CEST

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