Undo Block Allocation Algorithm in Automatic Undo Management
Hi,
Can someone please explain me the Undo Block allocation algorithm in Automatic Undo Management??
I need to tune my Undo tablespace in my Prod database.
regards,
Arul Sekar
Hi,
Thanks for the link provided.....
But the link which has been provided does not contain the details about the Undo block allocation alogorithm in AUM.
Can you please help me in this regard??
regards,
Arul Sekar
Similar Messages
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When are UNDO-Block written to disk ?
Hi,
does anybody know, when undo-block are written into the undo-tablespace?
1. When the dbbc is full?
2. when a checkpoint occurs
3. after 3 seconds ?
4. ???
Thanks
marcoYou've never done a hot backup? If a tablespace is taken offline or begin backup starts, either way, nothing is being written to files within that tablespace.
I can't believe this sort of thing still gets said from time to time.
It's completely wrong to say that when 'begin backup starts nothing is written to files within that tablespace'. Totally wrong.
Whether a file is in hot backup mode or not, DBWR must flush to it periodically (at a checkpoint, every three seconds, when a search threshold for a free buffer is exceeded etc) in order to keep the buffer cache functional. If it wasn't allowed to write to one or more files because they're in hot backup mode, eventually the cache would fill with dirty buffers with nowhere to flush them to and then your database would hang. It's simply not logical to think that 'begin backup' somehow puts a ring-fence around a file. If that were true, performing a hot backup would come with a big caveat: "Finish this backup in X minutes or less otherwise your database will hang".
But people have left files in hot backup mode for weeks and months at a time, and that simply doesn't happen, so it can't be true. (And not only can't it be true, but it in fact and as a matter of testable functionality -i.e, select phywrts from v$filestat during a hot backup and you'll see them increment- isn't true.)
The only thing the begin backup command does is to prevent CKPT writing to the file header (so the checkpoint change number can't get incremented). That's it. Everything else about the way DBWR and your Server Process works behaves completely normally.
That's true, also, whether the dirty buffers in question belong to EMP, PK_EMP_IDX or _SYSM0000$8: a rollback/undo block is no different as far as DBWR is concerned than a block from a "normal" table or index. They're just segments, all of them. The fact that one gets a special name ("undo segment") is irrelevant: it's just storing data like EMP is, and is flushed when any other dirty buffer would be.
Yes, of course this means you file copy will be "fuzzy". It's not an accident that Oracle won't even let you put a tablespace into hot backup unless you're in archive mode: it's known ahead of time that the copy will potentially be fuzzy and will need to be recovered before it can be made usable. So you have to be in a state where that redo can be guaranteed to be created before it makes sense to let you try making hot, fuzzy copies.
The fuzziness in the datafile copy isn't an issue precisely because, as you mention later on, Oracle writes a non-fuzzy copy of the block into the redo stream before the first change in hot backup mode is allowed to be made to it. Therefore, if the block image in the file copy is later discovered to be 'fuzzy', a good copy can be written over the top of it, sourced from redo. -
Automatic Undo Management - Shrink Undo Segments
Hello guys,
i have a question regarding the automatic undo management and some large transactions.
So lets take the following example:
1 transaction with a lot of updates (round about 20.00000 entries) . After the update a commit was executed.
Now the corresponding undo segment was blown up to 640 MB.
Now my questions:
Will this segment be shrinked after it is not needed anymore (STATUS = EXPIRED)?
If not and another transaction needs some undo and activates this segment again.. 640 MB are going online again... but the transaction now only needs some KB.
I know the algorithm if the undo segment needs to be extended (metalinknote #413732.1).. but what is happening to "big" segements if they are not needed anymore ... are the deallocated/shrinked after a time period?
Regards
StefanHere is a little example of a smaller undo segment.. which shows my doubt:
SELECT SEGMENT_NAME,STATUS FROM DBA_ROLLBACK_SEGS WHERE SEGMENT_NAME = '_SYSSMU13$';
SEGMENT_NAME STATUS
_SYSSMU13$ OFFLINE
SELECT SEGMENT_NAME, EXTENT_ID, BYTES, STATUS from DBA_UNDO_EXTENTS WHERE SEGMENT_NAME = '_SYSSMU13$';
SEGMENT_NAME EXTENT_ID BYTES STATUS
_SYSSMU13$ 0 65536 EXPIRED
_SYSSMU13$ 1 65536 EXPIRED
_SYSSMU13$ 2 8388608 EXPIRED
_SYSSMU13$ 3 8388608 EXPIRED
_SYSSMU13$ 4 8388608 EXPIRED
_SYSSMU13$ 5 8388608 EXPIRED
_SYSSMU13$ 6 8388608 EXPIRED
_SYSSMU13$ 7 8388608 EXPIRED
_SYSSMU13$ 8 8388608 EXPIRED
_SYSSMU13$ 9 8388608 EXPIRED
_SYSSMU13$ 10 8388608 EXPIRED
_SYSSMU13$ 11 67108864 EXPIRED If the other guys are correct, the extents of undo segment _SYSSMU13$ should be deallocated... but they still persist.
Regards
Stefan -
if we use automatic undo management in oracle database, may we still have a chance to get ERROR"Snapshot too old" or it may be avoided as Oracle manages undo segments itself....
RegardsIf you are 9i this note is worth a look:Note:301432.1Performance Slowdown During Heavy Undo Segment Onlining
I have discussed about this topic at my blog:
http://jaffardba.blogspot.com/
The question was about 'Sanpshot too old eror', not about the performance related to AUTOMATIC UNDO.
One more parameter that may cause is undo_retention.
The other work around to avoid is to run the most long query and use v$undostat view and set the undo tbs and undo_retention parameters.
Jaffar -
Hello
1-)
Suppose undo tbs is 10gb.
There is no activity in the database and hence Oracle decided to take the rollback segments offline.
Does it also drop the rollbacksegments?
I mean, is there a chance to reduce my undo tablespace 10gb to 8gb automatically?
2-)
I know that round robin is used in manuel undo, Is it same in AUM?
Suppose
transaction1 assigned to rbs1
transaction2 assigned to rbs2.
transaction3 assigned to rbs3
Assume, transaction2 commited. and undo retention period is expired.
Does transaction4 assigned to rbs2 or rbs1?John Carew wrote:
2-)
I know that round robin is used in manuel undo, Is it same in AUM?No. I haven't worked out in any detail how Oracle behaves, but it has some algorithm for minimising the number of undo segments used over time. (Essentially it seems to follow a "re-use recent victim" approach - which is why undo segments can end up being automaticallly taken offline and even (I think) dropped.
Suppose
transaction1 assigned to rbs1
transaction2 assigned to rbs2.
transaction3 assigned to rbs3
Assume, transaction2 commited. and undo retention period is expired.
Does transaction4 assigned to rbs2 or rbs1?I think it will go to rbs2 - because part of the selection algorithm aims to avoid having multiple transactions attached to a single undo segment if possible. (But, of course, there may be some other undo segment which is considered a better target for other reasons).
Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com
http://www.jlcomp.demon.co.uk
To post code, statspack/AWR report, execution plans or trace files, start and end the section with the tag {noformat}{noformat} (lowercase, curly brackets, no spaces) so that the text appears in fixed format.
"Science is more than a body of knowledge; it is a way of thinking"
Carl Sagan -
Illegal rollback Segment operation in Automatic Undo mode
Hi,
I use oracle database 9.2.0.1 and I try to install SCM repository but when I run ckcreate I saw an error message in
the log file that Illegal rollback Segment operation in Automatic Undo mode because oracle 9.2 use automatic undo mode .So how can i install the repository.
Ghassan HallaqORA-30019: Illegal rollback Segment operation in Automatic Undo mode
You have hit bug '2108361'. I think you could safely ignore it in your case. -
Hallo,
I have an ORA-00600 with [4194] which indicates an undo block corruption (as far as I know).
Does anyone know how to deal with this ?
Regards,
MynzHi Mynz,
But how does it help me to go on ?Here are my notes on repairing undo corruption:
http://www.dba-oracle.com/t_fix_undo_log_corruption.htm
I would open an SR and note that there are undocumented parms to help, BUT only when advised by Oracle tech support:
http://www.dba-oracle.com/t_8i_hidden_corruption_recovery_parameters.htm
Hope this helps. . .
Don Burleson
Oracle Press author -
MCU Send assignment is not reflected in automatic channel management
I have discovered a problem where the MCU Send assignment, is not reflected in automatic channel management.
Can someone try this for me please, with a session that has for 'Automatic Management of Channel strips' enabled...
Press and hold 'Send' -- then push v-pot 7 for the function 'Send, destination and level' for the v-pots.
If you assign an Aux that has not been used, it will not be created automatically.
Cheers,
MattAutomatic Shared Memory Management Enabled
Total SGA Size (MB) 3840
SGA Component Current Allocation (MB)Check the value of your MEMORY_MAX_TARGET and MEMORY_TARGET setting in 11g these two parameter enable auto shared memory management.
the values of SGA_TARGET and PGA_AGGREGATE_TARGET act as minimum values for the sizes of the SGA or instance PGA if set to non-zero.
SHOW PARAMETER TARGET
http://download.oracle.com/docs/cd/B28359_01/server.111/b28310/memory003.htm#BGBJAHEJ -
Automatic Cr. Management :Sales order blokced for Delivery
Hi.
I have done the Automatic Credit Management.
I would like to block the sales order from being delivered. The delivery block needs to be set to "01 Credit limit"
I have done the following settings.
In the Definition of Sales Order,
Check Credit Limit : D
In the Definition of Item Category,
Credit Active field is checked.
Order type is assigned to the credit check type D and Group 01 in OVAK.
In ova8, for this combination of the Cr. Ctrl area /Risk category / Cr. Grp.
Dynamic -ticked
Reaction A
Status/ Block - Ticked
FD32 is done.
Did i miss any customizing here? i would like to have the Auto Cr. Management (D)and not the simple cr. check(A, B or C)
Do reply.
thanks
VenkatHello Venkat,
Below is whole procedure for Aut Crdt Mgmt.
1. Transaction OB38
Check which credit control area is assigned to the company code.
Company code:
Credit control area:
2. Transaction OVFL
Check which credit control area is assigned to the sales area.
Sales area:
Credit control area:
3. Transaction XD02 or VD02
Check which credit control area is assigned to the payer.
Payer:
Credit control area:
4. Transaction SE37
Is user exit EXIT_SAPV45K_001 being used?
5. Transaction OBZK
For the settings under items 2 - 4, field "All company codes" must be marked in Transaction
OB45, or the credit control area must be entered under the relevant company code in table
T001CM of the credit control areas allowed.
Company code:
Credit control areas allowed:
6. Settings for the credit checks
7. Transaction OVAK
Which settings do exist for the sales document type used?
Sales document:
Check credit:
Credit group:
8. Transaction OVAD
Which settings do exist for the delivery type used?
Delivery type:
Credit group for delivery:
Credit group for goods issue:
9. Transaction OB01
Credit management/Change risk category
Definition of the risk category for each credit control area. This risk category can be
assigned to a credit account by using Transaction FD32.
10. Transaction OVA8
Here, the individual credit checks for key fields
o credit control area
o risk category
o credit group are set. Take these key fields from the above settings and go to the detail
screen. In particular, check whether fields "Reaction" and "Status/block" are set
correctly. To carry out follow-up actions in case of a credit block, the credit check
status must be set (field "Status/block").
11. Transaction FD32
Credit master data for the payer of the relevant document.
Credit account:
Credit limit:
Risk category:
Currency:
12. Settings for updating the credit values Update of the credit values is required for the limit
check (static or dynamic credit limit check).
13. Transaction OVA7
Update of the credit value is active for the corresponding item type if the check box is marked. This field corresponds to
field "Active receivable" in Transaction VOV7.
Item type:
Active receivable:
14. Transaction V/08, Pricing
In the pricing procedure used for pricing, subtotal "A" must be entered in a line for
determining the credit value (mark the pricing procedure and doubleclick on "Control").
Usually, the net value plus taxes is used. This way the system is determined to use this
subtotal for credit pricing. The credit price is stored in field VBAP-CMPRE and used for
update and credit check.
You can find the used pricing procedure of the order under "Item -> Condition -> Analysis".
Pricing procedure:
Line with subtotal = 'A':
15. Transaction OB45
Which update group (field "Update") do you use in the relevant credit control area? The
default setting is "12". If you use another update group, check whether this is fine with
you. If you open an OSS message, please tell us the alternative update group.
Credit control area:
Update:
REWARD POINTS IF U FIND THIS AS USEFUL...
Regds
MM -
Question about 11gR2 Grid, RAC, /dev/shm and Automatic Memory Management
Hello,
i've recently installed grid and rdbms software 11.2.0.2 on a two node Oracle Linux cluster with 128gb ram each node.
I'm using ASM to store data and ocr and I'm testing Automatic Memory Management.
When I finished Grid+RDBMS installation I've seen that /dev/shm size is 64gb (half of my total RAM).
I've created a database with dbca and when I was asked to choose if I wanted to use AMM I've noticed that I could
allocate only about 60gb for Oracle. If I chose more than 90gb I got an error saying:
Using Automatic Memory Management requires 60gb available in my two nodes.
The current available space in the two nodes is only 30gb and 30gb.
If you want to use AMM you should either free up some space in /dev/shm
or reduce the memory allocated to Oracle
I was wondering when (during the installation or the settings of kernel parameters) did I define the space of /dev/shm ?
Since I have 128gb of RAM wouldn't it be better to use more than 64gb of ram for my /dev/shm tmpfs partition ?
Is there a limit or a ratio for best practice for my RAM and the /dev/shm ?
thanks in advance.user9051299 wrote:
Is the "half of the RAM size" a kernel's default value or Oracle's ? Neither. There are a number of unique factors that determine the best memory size and fit for Oracle - including just how much memory is effectively available (i.e. how much is needed for other services and processes).
And from what I understand i don't "break" any Oracle's best practice by increasing the /dev/shm right ?Correct. (at least none that I'm aware of, and none that I have read in Oracle's RAC Starter Kit documentation). -
How do you set Automatic Acoustic Management (AAM) for new Hard Drive?
I have a new hard drive that I'm about to have installed into my iMac. The drive is a WD1001FALS (Western Digital Caviar Black 1TB). The only concern I have is that by all accounts it is a bit louder than some other drives, although everything being relative I don't know what that means to me since I've not heard it run yet.
Still, the 320GB drive currently in the iMac is absolutely inaudible and while I'll make some concessions for speed and size I'd like to minimize the amount of noise coming out of the box. I know that the drive supports Automatic Acoustic Management (AAM), however its default state is "disabled". Is there a way, either through the OS or third party software to enable this feature?I just wanted to close out this question.
I never received a clear answer but in the end I don't need to use the function. My concern was that a new WD1001FALS would be louder than the OEM 320GB HDD in my iMac to the point that I wouldn't be happy with it. Not wanting to trade speed for quiet I passed on the Green caviar and went for the Black. After living with it for several weeks I can say that it is very quiet and while I don't know if it's measurably louder than the old drive, it's not enough for me to notice (and I'm pretty picky).
So, I'm happy with the drive as-is, case closed. -
Oracle 11g AMM (Automatic Memory Management)
Hi All,
I have a very powerful server 24 Processors with 6 cores each and 74 GB RAM for my production database. The server will host only one production database. I wanted to use AMM for this database and allocate maximum memory to Oracle by setting memory_target. By default /dev/shm is set 37 GB but I wanted to increase it least 55 GB. I know I can get this changed by my system admin but I wanted to know how much memory should leave for OS?
Please help me on sizing this.
Thanks,
Arun SinghFrom MOS ID 169706.1
Automatic Memory Management
Starting with Oracle Database 11g, the Automatic Memory Management feature requires more shared memory (/dev/shm) and file descriptors. The shared memory should be sized to be at least the greater of MEMORY_MAX_TARGET and MEMORY_TARGET for each Oracle instance on the computer. To determine the amount of shared memory available, enter the following command: # df -k /dev/shm/
Note: MEMORY_MAX_TARGET and MEMORY_TARGET cannot be used when LOCK_SGA is enabled or with huge pages on Linux -
RE: During MIRO payment block indicator piks up automatically
Hi All,
Can anyone tell me about this issue:
My user is doing MIRO at that time Payment block indicator picks up automatically for some invoices randomly what could be the reason.
1) there is price differences MIGO and MIRO the same
Pleas let me know the possible reasons to check in my case.
points will be assigned.Hi,
When you enter an invoice, the system suggests the values that it expects an invoice to contain as a result of the purchase order or goods receipt. If the invoice item differs from the default values, you must determine the reason for the variance by contacting the purchasing or goods receiving department or the vendor.
If a tolerance limit is exceeded, you receive a system message. You can post the invoice in the system, but it is automatically blocked for payment if an upper tolerance limit is exceeded.
An invoice can be blocked for payment due to one of the following reasons:
u2022 Variance in an Invoice Item
u2022 Amount of an Invoice Item
u2022 Stochastic Block
u2022 Manual Block
When an invoice is blocked, Vendor cannot be paid. Invoices can be blocked either automatically or manually. You can block an item by selecting the Ma (manual blocking reason) field in the item list.
When you post an invoice, two things happen:
u2022 The account postings resulting from the invoice are made.
u2022 In the vendor line of the accounting document, the system enters an u201CRu201D in the field Payment block so that Financial Accounting cannot make payment for the invoice.
I hope this will solve your doubt.
Regards,
Kapil -
In preferences what does "Override automatic cache management" mean and do?
I was wondering what "Override automatic cache management" means and does.
Firefox normally manages the size of it's cache, and can cache more or less information depending on various factors.
Checking this option allows you to specify the maximum size of the Firefox cache, in MB.
There isn't usually any need to enable this option. -
INS-20802 Automatic Storage Management Configuration Assistant Failed
Dear all,
Please help me to fix this issue, when I install grid infrastructure I have encounter a problem which describe INS-20802 Automatic Storage Management Configuration Assistant Failed.
Could anyone help me to find out this problem?
Thank before hand for you help.
Best Regards,
Vouthea OUNDear all,
Please help me to fix this issue, when I install grid infrastructure I have encounter a problem which describe INS-20802 Automatic Storage Management Configuration Assistant Failed.
Could anyone help me to find out this problem?
Thank before hand for you help.
Best Regards,
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