Re: Undo Tablespace Error

It is possible that the datafile was manually resized to 200GB by a DBA. Since the current size exceed the MAXSIZE, the datafile cannot autoextend.

Hemant K Chitale

On Wed, Sep 8, 2021 at 9:00 PM Lok P <loknath.73_at_gmail.com> wrote:

> 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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