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Recommendations/Doubts - log_buffer size and Oracle redo log file size.

Hello,

I´m adjusting some oracle parameters but now I´m with some doubts regarding the log_buffer size value!

This is a production SAP system running on Oracle DB 11.2g (11.2.0.4) in a Windows Server 2012 (R2). The server has 24Gb of RAM memory and 8 CPU´s.

Some questions/doubts:

1. Which unit the log_buffer has? Bytes? (The default value in my database is 14254080).

2. I read the sap note 1431798 (Oracle 11.2.0: Database Parameter Settings) and then the sap note 1627481 (Preemptive redolog switches in Oracle 11.2 and higher) and in this last one I read some requirements (my server has 8 cores):

For systems with <= 16 cores set the logbuffer to 4MB or don't set it at all.

So... I changed the value (consider that parameter is in bytes unit) to 4194304 bytes (4 megabytes)

This is a good decision or not? Tell me your opinion please.

3. In the same sap note 1627481 I see the following statement:

If you have set the logbuffer to 4MB, then create redo logfiles of at least 200MB.This minimum configuration should only be used for DEV, Test or QA systems but not for production systems.

But I don´t understand... as I said before I set the log_buffer to 4MB but now I want to know which value I must set to the redo logfiles (origlogs and mirrlogs) in a production system. As you see the sap note only described the value for DEV, Test or QA systems, not for the production systems.

Which value is recommended for redolog files?

Can you answer to these three questions?

Any other recommendations?

Thank you,

Best regards,

João Dimas

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2 Answers

  • Mar 30, 2016 at 01:59 PM

    Hi,

    do not set log_buffer, Oracle will autotune it depending on several factors. On our dev system log_buffer is 28MB and on our production 120MB.

    Set the redolog file size big enough e.g. 1GB and set archive_lag_target to e.g. 1800 (30Min). This means that the redolog switches every 30min also if the redolog is not filled up.

    Regards Marc

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  • Mar 27, 2016 at 10:44 PM

    Hello,

    No one answered to my questions 😔... can anyone answer to my doubts please?

    Thank you,

    Best regards,

    JD

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    • Former Member James Zhang

      Hi JD

      1. log_buffer unit is in "byte" so calculate it size accordingly.

      2. As per snote#1627481, it should be ok either you set log_buffer to 4MB or not, you can increase the redolog file size upto 1GB for production system as per your server CPU config.

      Best regards

      Ketan Bhut