Re: Undo Tablespace Error

Thank you Hemant.

*to your point "Besides dba_hist_tbsp_space_usage you should also look at v$undostat"*

This error occurred to us 4-5days ago. So from min(begin_time) , I am seeing it doesn't have those time data in v$undostat anymore. So is there another way to dig into history?

If i see current values in v$parameter, We have UNDO_MANGEMENT set as AUTO undo_retention set as 3600. If I see current values in dba_data_files we have only one data file for the UNDo tablespace. and it has BYTES as 200GB, MAXBYTES- 160GB, USER_BYTES- 200GB, Autoextensible- YES. So in this case do you suggest just by turning OFF the AUTOEXTEND , we should be good to avoid this issue in future?

But I had one question, even if we have AUTOEXTEND ON, as we have defined the MAXBYTES as ~160GB for that data file, so that is as good as AUTOEXTEND OFF having same maxBytes as ~160GB as because in both of the cases it can't go beyond 160GB. Is my understanding wrong here?

On Wed, Sep 8, 2021 at 8:14 AM Hemant K Chitale <hemantkchitale_at_gmail.com> wrote:

>
> If you have AUTOEXTEND ON it is likely that the datafile had already hit
> the MAXSIZE.
> So this would result in failure 6 in Oracle Support document " Troubleshooting
> ORA-30036 - Unable To Extend Undo Tablespace (Doc ID 460481.1)
>
> Besides dba_hist_tbsp_space_usage you should also look at v$undostat
> (also in earlier versions dba_hist_tbsp_space_usage had bugs in reporting
> Tablespace Usage for Undo tablespaces)
>
> As John says, if you have AUTOEXTEND ON, Oracle will try to keep
> extending Undo retention. Setting a max size for the datafiles and then
> setting AUTOEXTEND OFF is better.
>
> Hemant K Chitale
>
>
>
>
> On Mon, Sep 6, 2021 at 2:59 AM Lok P <loknath.73_at_gmail.com> wrote:
>
>> Thank You John. I understand your point that with AUTOEXTENSIBLE YES
>> oracle may tend to keep the expired UNDO longer to satisfy retention
>> thereby increasing the UNDO tablespace to higher size. But , If we will
>> talk specifically about the exact error here , isn't it true that with
>> AUTOEXTENSIBLE YES, it should not have made it errored out with Ora-30036
>> rather it would have thrashed/increased UNDO tablespace size by its own?
>>
>> Also as I see from dba_hist_tbspc_space_usage , the UNDO
>> usage(tablespace_usedsize) was ~160GB which was equal to tablespace_size
>> when it failed with ora-30036 , but then it increased to ~200GB after
>> 4-5hrs, yet to see if somebody has increased it manually or it increased by
>> itself.
>>
>> On Sun, Sep 5, 2021 at 2:53 AM John Piwowar <jpiwowar_at_gmail.com> wrote:
>>
>>> The “autoextensible” setting on your undo data files is possibly the
>>> culprit here. Undo segments are a bit of a special case, and Oracle’s
>>> decision-making about when to reclaim expired undo can be thrown off when
>>> it thinks it has the option to extend a data file instead. It’s possible
>>> that you might still need to resize your undo to accommodate recent changes
>>> in your workload, but you’re better off with fixed-size undo datafiles,
>>> followed by an examination of your automatic undo configuration
>>> (undo_retention, etc).
>>>
>>> Sorry about the vagueness of the response; I’m on my phone and can’t get
>>> decent references with my thumbs. :)
>>>
>>> On Sat, Sep 4, 2021 at 1:05 PM Lok P <loknath.73_at_gmail.com> wrote:
>>>
>>>> Hello Listers, In one of our 12.1 version databases, a few days back we
>>>> encountered an error- "Ora-30036 Unable to extend segment by 128 in
>>>> tablespace 'UNDOTBS1'" for a delete query. This failure has never happened
>>>> before. And we were trying to see if we really have to increase the size of
>>>> UNDO tablespace(current size is ~200GB) as it has other impacts like making
>>>> long running queries run even longer before hitting ora-01555/snapshot too
>>>> old etc. Or anyway we can track and fix the long transactions which might
>>>> have consumed large UNDO during that time and then we can try to break that
>>>> into small transactions?
>>>>
>>>> Another thing I notice in the dba_data_files is now showing
>>>> autoextensible as YES, so how come this query errored out with
>>>> Ora-30036/space issues?
>>>>
>>>> The USED space in dba_hist_tbspc_space_usage for this UNDO tablespace
>>>> is sometimes showing completely full and sometimes it's a lot empty and i
>>>> believe it's because of a circular buffer.
>>>>
>>>>
>>>> --
>>> Regards, John P. (Typed with thumbs on a mobile device. Lowered
>>> expectations appreciated)
>>>
>>

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