Undo Tablespace Management
Apr 23, 2013
I am trying to drop 90 columns from a big partitioned table. I was trying a physical drop first and since it is taking longer time I decided make the columns unused state and drop them. However I was able to set them to unused state.
Now I am trying to drop those unused columns from the table, it is running since 22hours Apporox. I am keep increasing the undo tablespace to retain the undo data.
I also have decreased the undo_retention to 300 from 900.
My question is there any better way to drop these columns. And is there any way to flush out the data from undo.
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Jan 30, 2004
regarding sizing undo tablespace and undo_retention parameter.we have to implement the database in production system with 40 users but how much space should be allocated to undo tablespace is there any propotions related to virtual memory and the
parameter.i have gone thru oracle doc's and some related sites.its an ERP aplications that contains 20 modules .I am an new one to this dba level
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Jul 31, 2010
I have been reading various articles about the undo management. This basic concept of undo management is simple but how oracle implements it is bit harder for me to grasp.
What i have read and understood is that whenever a DML(Update, Delete, Insert) statement is issued by a user, the data is fetched from datafile to database buffer cache and at the same time a copy of the original data is saved in undo segment. Now if other users requests the same data, they are presented with the unchanged copy in the undo segment.
Now I have the following questions:
1) In case of Insert statement, what data is saved in undo segment. Is it the complete data in the table to which we want to insert the new row?
2)When the user issues DML statement, there are three copies of the same data, one in Memory (which is changed and not the same as original data), second in Undo segment (Which is unchanged copy of original data) and third in datafile file ( which is original data). What is the difference in the data in undo segment and data in datafile at this stage. Why are the other users presented with the data from undo segment rather than original data from the datafile to maintain read consistency.
3)When the user issues rollback, the changes made to the copy of data in memory are undone.The copies of data in memory and undo segment are now same?. What happens to the before change copy in undo segment. Is it still there or deleted.
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Jun 6, 2012
At a time my 20 GB undo tablespace was full. So i increased the tablespace size upto 48 GB. Then i saw 45 GB was used. Then i changed undo_retention=60. After that am seeing that 48 GB is full.
1) why it's happened?
2) Here what is the effect of undo_retention=60
3) How to resolve?.
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Apr 26, 2013
Can an undo tablespace be too large and actually hurt performance? I have seen a system with a dedicated 1 TB drive for undo tablespace (no guarantee) with an undo_retention of 7 days. Would this hurt performance? What about setting an undo_retention of 24 hours with no guarantee? The only mention I could find online said that it would not hurt performance but I wanted to double check. You would think that Oracle does not care if it deletes the undo at 15 minutes or if it deletes the undo at a later date such as 7 days later and the performance should stay the same.
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Apr 2, 2013
S:Solaris
DB:10g
I am simulating a recovery of drop undo tablespace. for the same I have done the following things:
1. Dropped the only undo datafile from the os level while the database was open.
2. Then I created a table and inserted and updated some values in it and I was also allowed to commit.
When I am updating the rows of the table,the before images must have been written to UNDO but in my case there is no UNDO datafile.
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Dec 23, 2012
i Cannot drop old undo tablespace. While dropping the old undo tablespace we get an error
ERROR at line 1: ORA-01548: active rollback segment '_SYSSMU77$' found, terminate dropping tablespace
SQL> select tablespace_name, status, segment_name from dba_rollback_segs where status != 'OFFLINE';
TABLESPACE_NAME STATUS SEGMENT_NAME
------------------------------ ---------------- ------------------------------
SYSTEM ONLINE SYSTEM
APPS_UNDO NEEDS RECOVERY _SYSSMU77$
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Aug 18, 2010
When i takeind export i got error like this..
ORA-39125: Worker unexpected fatal error in KUPW$WORKER.GET_TABLE_DATA_OBJECTS while calling DBMS_METADATA.FETCH_XML_CLOB [TABLE_DATA:"POS"."TBK_POS_FACT":"KROATL200404"]
ORA-01555: snapshot too old: rollback segment number 1 with name "_SYSSMU1$" too small"
from this can we increase the undo_retention value or undo tablespace size?
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Jan 17, 2007
I'm an Oracle novice and from what I've read so far, it seems that you should be able to do rollbacks and data recovery using the redo logs. I'm having a difficulty understanding the need for the undo tablespace.
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Apr 25, 2013
it seems that you should be able to do rollbacks and data recovery using the redo logs. I'm having a difficulty understanding the need for the undo tablespace.
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Feb 7, 2011
As the undo segments are used in round robin fashion, Is it possible that with varying load (concurrent users, size and number of transactions), the size of Undo tablespace on a particular day is less than the Undo tablespace size few days back, by any chance?
As a basic understanding I know that Undo is preserved for read consistency and transaction, instance recovery So if there are lot of transaction on a database on 05 Feb and before that, but there aren't any transactions on 6,7,8,9, then on 10th Feb can we see the Undo tablespace size is less than that of 05 Feb?
In the following case when data belonging to table is not required for any queries, transactions, even then the undo size is not restored upon dropping the table.
As such for large operations and batch processes shall we keep undo tablespace with files as 'Autoextend' with 'Maxsize' as 'Unlimited'?
SQL> select b.tablespace_name, Total_Kbytes_Available/1024 Tot_Mbytes_Available,
Kbytes_alloc/1024 Mbytes_allocated, kbytes_free/1024 Mbytes_Free_from_allocated,
((Kbytes_alloc - kbytes_free)*100/ Total_Kbytes_Available) Pctused
2 from ( select sum(bytes)/1024 Kbytes_free,
3 tablespace_name
4 from sys.dba_free_space
[code]....
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Jan 22, 2013
why total size for undotbs1 is different from the acutal data file size in Operating system.
select tablespace_name, sum(bytes/1024/1024) from dba_data_files
where tablespace_name like 'UNDO%'
group by tablespace_name;
tablespacename total size
UNDOTBS1 2000
UNDOTBS2 7284
[code]....
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Apr 14, 2013
rdbms 11gr2 undo tablespace is not fixed size. and the undo guarantee is not set.should we set undo_retention to
select max(tuned_undoretention) from v$undostat ; to avoid 1555 error?
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May 18, 2011
you have an undo tablespace which has autoextend on feature.after a timegap your undo tablespace presently is 100GB
here as a DBA what you will do?
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Apr 28, 2011
When I am importing, I get these errors
IMP-00019: row rejected due to ORACLE error 1
IMP-00003: ORACLE error 1 encountered
ORA-00001: unique constraint (XXXXXXXXXXXXXXXX) violated
Column 1 2
Column 2 OFFLINE
[code]....
I added a datafile in undo tablespace (its an ASM database). I doubt that since I added the datafile to undo tablespace, I am getting this error.
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Mar 24, 2013
Operating System - WindowXP
oracle version 10.2.0.1
I was learning some recovery part in my home laptop. Database is in Archivelog, flashback mode. All of sudden, i deleted it from OS level with out taking backup of it.
When i tried to open database, it failed to start. Database is in mount mode.while trying to open, it gives message -
ORA-01157: cannot identify/lock data file 1 - see DBWR trace file
ORA-01110: data file 1: 'F:ORACLEPRODUCT10.2.0ORADATADBSYSTEM01.DBF'
I tried to create on file named "UNDOTBS01.DBF" but oracle is not recognizing it.
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Mar 7, 2012
we have a situation where both undo tablespaces were almost filled i.e UNDOTBS1 99% and UNDOTBS2 100% filled so i add data files to it and then i found a lot of blocking session and was just killing them through EM then i stop my front end listener and also down the service, now i don't have any blocking session but on EM a big WAIT is coming. alert log shows nothing serious, it was showing deadlock but now it is over as well.
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May 30, 2013
I have a serious doubt in oracle architecture functionality, when a user issues a update statement the data blocks are carried to db buffer cache and where does the changes to the data blocks are made???? Does a copy of the data block is kept in db buffer cache and the changes are made to the block in buffer cache?? or the a copy of the data block is kept in undo tablespace and changes are made to the blocks in the undo tablespace???
In simple the changes to the data blocks are made at db buffer cache or undo tablespace?
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Jul 26, 2010
i'm facing a problem while i'm inserting millions of record from table to table that undo tablespace reach 100% full and execution aborted. , how can free the undo tablespace ??? many of extendes are offline. will it flush automatically ??? or what i should do
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Jun 16, 2013
i have 80 gb table d9040 which residing in separate tablespace in existing database(10g) OLTP .
i m going to import(impdp) an export(expdp) dump on 11r2 on which ASM is residing.
I have following two options available while importing
1.Put all the datafiles of that particular tabesace on a single disk .
or
2.Put half datafiles on disk 1 and remaining half on disk 2.
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May 22, 2012
how we can perform the tablespace management? monitor the tablespace and tune the tablespace space.
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Nov 29, 2012
Can we find out no of undo segments in undo Table space ? If so , how to find? what's their max limit ?
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Jan 18, 2012
How to import dump into specific tablespace instead of default tablespace users.
I want to import my dump file to newly created tablespace ,so how can i do that . I have created new user called cvm and while creating it i mentioned default tablespace to newly created tablespace . But when i try to import my dumo file it goes to users tablespace .
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May 27, 2011
i have a tablespace which contains 121 datafile(max limit reached) as a dba what we have to do?
creating a new tablespace with a datafile and assign the users to the current tablespace which i created now.iif the above process is correct,after some time the tablespace which was filled up got freed up.now can i give the access to the users previous (i.e. freed up tablespace) and current tablespaces
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Jan 26, 2011
My database version is
Oracle Database 11g Enterprise Edition Release 11.1.0.7.0 - 64bit Production
PL/SQL Release 11.1.0.7.0 - Production
CORE 11.1.0.7.0 Production
TNS for Linux: Version 11.1.0.7.0 - Production
NLSRTL Version 11.1.0.7.0 - Production
My os version is
Linux damdat01 2.6.18-128.7.1.el5 #1 SMP Wed
Aug 19 04:00:49 EDT 2009 x86_64 x86_64 x86_64
GNU/Linux
My database is OLP system.
My question is what are the advantages and disadvantages having one single tablespace versus multiple tablespace?
Easy to maintain when you have single tablespace. but hard to track the IO issues if you have one single tablespace.
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Mar 29, 2010
How to find out how much undo will be generated by a dml / ddl statement in Oracle 9i? With Oracle 10g we can use the famous mystat.sql and mystat2.sql with argument as 'undo change vector size'.
However with Oracle 9i there is no statname as 'undo change vector size'
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Jul 13, 2013
Flashback query is working fine for dropped table,but throwing error when trying to get back the previous date by dropping a column from a table.
FLASHBACK TABLE emp TO TIMESTAMP TO_TIMESTAMP('2013-07-13 05:00:00', 'YYYY-MM-DD HH24:MI:SS')
SQL Error: ORA-01466: unable to read data - table definition has changed
Is that a limitation of Oracle by not having query to flashback a column but a table.
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Jan 15, 2012
Query to find out who is eating up most of the undo space and what query he is running..
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Feb 24, 2013
How do I perform Undo a drop table operation?
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Apr 10, 2013
During rollback phase of instance recovery, where is the undo applied from:
- redo logs
or
- undo generated during redo application in roll forward phase?
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