RE: Query ASH for Undo Blocks

From: Noveljic Nenad <nenad.noveljic_at_vontobel.com>
Date: Mon, 13 Jun 2022 11:01:33 +0000
Message-ID: <ea0d056f648d4c779dafc60ba66264e8_at_vontobel.com>

I think yes, but it's only useful in the case when the buffer gets result in read wait events. But what if all the undo blocks needed are already cached?

You can check if the session statistics for "%undo records applied" is increasing: https://asktom.oracle.com/pls/apex/f?p=100:11:::::P11_QUESTION_ID:9542989000346736054

Alternatively, you can trace the Oracle C function kcbgtcr with bpftrace.

Best regards,

Nenad

-----Original Message-----

From: oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> On Behalf Of Lothar Flatz Sent: Montag, 13. Juni 2022 12:36
To: oracle-l_at_freelists.org
Subject: Query ASH for Undo Blocks

• E-Mail from outside Vontobel: Do not click on links or open attachments unless you know the content is safe. ***

Hi,

there is a plan with an Index Range scan that generates way more buffer_gets than you would expect. Would it be correct to query active session history using CURRENT_FILE# and CURRENT_BLOCK# to check against DBA_EXTENTS to find out if some buffer gets are coming from undo? The query does work, but i am not sure if the result is showing the indented answer.

Thanks

Lothar

--

http://www.freelists.org/webpage/oracle-l

---

Please consider the environment before printing this e-mail. Bitte denken Sie an die Umwelt, bevor Sie dieses E-Mail drucken.

Important Notice

This message is intended only for the individual named. It may contain confidential or privileged information. If you are not the named addressee you should in particular not disseminate, distribute, modify or copy this e-mail. Please notify the sender immediately by e-mail, if you have received this message by mistake and delete it from your system. Without prejudice to any contractual agreements between you and us which shall prevail in any case, we take it as your authorization to correspond with you by e-mail if you send us messages by e-mail. However, we reserve the right not to execute orders and instructions transmitted by e-mail at any time and without further explanation. E-mail transmission may not be secure or error-free as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete. Also processing of incoming e-mails cannot be guaranteed. All liability of Vontobel Holding Ltd. and any of its affiliates (hereinafter collectively referred to as "Vontobel Group") for any damages resulting from e-mail use is excluded. You are advised that urgent and time sensitive messages should not be sent by e-mail and if verification is required please request a printed version. Please note that all e-mail communications to and from the Vontobel Group are subject to electronic storage and review by Vontobel Group. Unless stated to the contrary and without prejudice to any contractual agreements between you and Vontobel Group which shall prevail in any case, e-mail-communication is for informational purposes only and is not intended as an offer or solicitation for the purchase or sale of any financial instrument or as an official confirmation of any transaction. The legal basis for the processing of your personal data is the legitimate interest to develop a commercial relationship with you, as well as your consent to forward you commercial communications. You can exercise, at any time and under the terms established under current regulation, your rights. If you prefer not to receive any further communications, please contact your client relationship manager if you are a client of Vontobel Group or notify the sender. Please note for an exact reference to the affected group entity the corporate e-mail signature. For further information about data privacy at Vontobel Group please consult www.vontobel.com <https://www.vontobel.com>.
--

http://www.freelists.org/webpage/oracle-l Received on Mon Jun 13 2022 - 13:01:33 CEST