Re: wrong start_time and start_date in v$transaction

Anything in any of the alert logs about processes not starting up properly, or using some specific function that doesn't get mentioned in other alert logs?

Are any of the funny instances running on virtual machines ? I recall a case where running on vmware some processes would intermittently record a "tim=" value in a trace file that was millions of centiseconds wrong.

Regards
Jonathan Lewis

On Tue, Sep 1, 2020 at 10:26 AM Noveljic Nenad <nenad.noveljic_at_vontobel.com> wrote:

> Jonathan,
>
> Clay,
>
>
>
> Only a minority of databases is affected by this problem. Other databases
> running on the same server and under the same Oracle home are healthy. I
> couldn’t find any difference between databases that work and those which
> don’t.
>
>
>
> I discovered that 12.2 is affected too (I originally reported the problem
> for 18c and 19c)
>
>
>
> v$transaction_time.start_date und start_time are constant for every
> transaction and every session on an affected database. This value doesn’t
> change over time. Consequently these it isn’t function of v$timer.hsecs.
>
>
>
> v$transaction_time.start_date is some arbitrary time higher than
> startup_time, for example.
>
>
>
> select
>
> 2 ( select start_date from v$transaction )
>
> 3 -
>
> 4 ( select startup_time from v$instance )
>
> 5 from dual ;
>
>
>
> (SELECTSTART_DATEFROMV$TRANSACTION)-(SELECTSTARTUP_TIMEFROMV$INSTANCE)
>
> ----------------------------------------------------------------------
>
> 70.2931366
>
>
>
> V$transaction.start_date is different on each database. Alert.log doesn’t
> show any anomalies around this time.
>
>
>
> After a database restart start_date gets populated correctly.
>
>
>
> Best regards,
>
>
>
> Nenad
>
>
>
> http://nenadnoveljic.com/blog/
>
>
>
>
>
>
>
> *From:* oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> *On
> Behalf Of *Clay Jackson (cjackson)
> *Sent:* Dienstag, 1. September 2020 00:11
> *To:* jlewisoracle_at_gmail.com; ORACLE-L (oracle-l_at_freelists.org) <
> oracle-l_at_freelists.org>
> *Subject:* RE: wrong start_time and start_date in v$transaction
>
>
>
> But, didn’t Nenad say “start_time doesn’t change over time on the affected
> databases”.
>
>
>
> Could it be as simple as the start time of the instance?
>
>
>
> But then why SOME transactions and not ALL? Perhaps something as simple
> as “the first transaction in each session”?
>
>
>
> Clay Jackson
>
>
>
> *From:* oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> *On
> Behalf Of *Jonathan Lewis
> *Sent:* Monday, August 31, 2020 2:54 PM
> *To:* ORACLE-L (oracle-l_at_freelists.org) <oracle-l_at_freelists.org>
> *Subject:* Re: wrong start_time and start_date in v$transaction
>
>
>
> *CAUTION:* This email originated from outside of the organization. Do not
> follow guidance, click links, or open attachments unless you recognize the
> sender and know the content is safe.
>
>
>
> Nenad,
>
>
>
> How about one "what if" (based on a bug pattern seen in an older version
> of Oracle) before doing anything complicated.
>
> What if: the thing creating the timestamp for the transaction is dividing
> a counter by the wrong power of 10 before adding seconds to the database
> startup time. If you check v$instance.startup_time + v$timer.hsecs/(100 *
> 86400) at the start of the transaction that should (I think) be very close
> to sysdate: can you get your transaction start time by dividing hsecs by a
> couple more powers of 10 ?
>
>
>
> Regards
>
> Jonathan Lewis
>
>
>
>
>
>
>
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