Rollback segment and log files

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  -A table space can contain a number of files, each consisting of a number of segments of. ?

  True and true half. Segments in a tablespace may extend in all, part or all of the data in this table files. User has no command to specify what datafile inside a tablespace should be used for a segment.

  but where information held relating to the global table

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  CREATE TABLE MEM_NBR
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• user managed backup and deferred tax rollback segments

  Hi Forum,

  Greetings of the day,

  Here I have a question about segments of rollback backup and deferred users managed, I don't have much experience with the user managed backups taken by backup of BEGIN and END.

  1. how facilities oracle using the database so that it is saved each tablespace, he will use deferred rollback segments?

  2. placing the tablespace in backup mode is the same as read-only mode, on a technical level. So that it can read the blocks and changes made by the user can be moved to deferred rollback segments and later applied to tablespace, when it is the backup of the END?

  3.AFAIK, will be created only to deferred rollback segments in the SYSTEM tablespace. So we need to keep an eye on the growth of the tablesace SYSTEM while the database/tablespace is backed by this method?

  4. when the tablespace is put out of backup by using the backup of the END , will be that it applied by the deferred rollback segments?

  5. where oracle will place deferred rollback segments, when tablesapce SYSTEM itself is implemented backup START ?

  6. DON'T face us any kind of failures during all backup /END START as full tablespace etc SYSTEM.

  Your answers will really helpful.

  Thank you

  Uday

  Here I have a question about segments of rollback backup and deferred users managed, I don't have much experience with the user managed backups taken by backup of BEGIN and END.

  1. how facilities oracle using the database so that it is saved each tablespace, he will use deferred rollback segments?

  In what context you mention the use of rollback differed with the backup segments maintained by users?

  2. placing the tablespace in backup mode is the same as read-only mode, on a technical level. So that it can read the blocks and changes made by the user can be moved to deferred rollback segments and later applied to tablespace, when it is the backup of the END?

  Do you mean to say that when the tablespace is backed up, it is not accessible to the DML? If so, this is a wrong concept. Oracle did not go for the rollback segment (which I do not know how you are linking anways), but maintains the writing the image in full blocks for the first time in the log files of recovery following the normal writing changed buffers.

  3.AFAIK, will be created only to deferred rollback segments in the SYSTEM tablespace. So we need to keep an eye on the growth of the tablesace SYSTEM while the database/tablespace is backed by this method?

  Response above asked about segment deferred cancellation and their relationship, according to you, with the backup tablespace?

  4. when the tablespace is put out of backup by using the backup of the END , will be that it applied by the deferred rollback segments?

  5. where oracle will place deferred rollback segments, when tablesapce SYSTEM itself is implemented backup START ?

  6. DON'T face us any kind of failures during all backup /END START as full tablespace etc SYSTEM.

  Seems that you don't really have an idea how the backups managed by users actually work. I'll suggest that you read about it first in the backup and restore documentation before entering in any event.

  HTH

  Aman...

• URL and monitoring of log files by using Foglight

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  Hope this helps.

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• Peformance Gain for a different drive for the SQL Server data and log (VM) file?

  Hello

  It is suggested to separate SQL Server 2012 data and log files in different drive for VM.  Is there a performance gain if two of them resided in the same logical (Partition VMDK) unit number?  OR should they (different dives) in different LUNS (Partition VMDK)?

  Thank you

  The General mantra in the physical world goes as follows:

  For optimal performance, you need to separate logs and database of transactions on different physical disks (e.g. disks) stacks.

  
  

  This general concept applies naturally agnostically to virtual workloads as well. It essentially translates to:

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• regarding cancellations and rollback segments

  Hello
  
  I read Undo records can be stored in two segments of rollback or undo some tablespaces.
  
  When they stored in undo and when they stored in rollback segments.
  and what is the relationship between the em?
  
  Thank you
  Vijay

  However, you must understand that "transactions_per_rollback_segment" does not mean that it is a limit on the number of transactions that supports a rollback segment!
  This setting is used by Oracle to determine the number of segments of rollback it must bring online when you open a database instance.
  This applies not to the segments 'TYPE 2 UNDO' that are automatically created and managed (online, taken offline, created, abandoned as needed) when you use UNDO_MANAGEMENT = 'AUTO '.

  Hemant K Collette

• Expectations extended on synchronization of log file while the parallel writing journal is fine

  We have 9.2.0.8 as experiences of long waits on the database log file sync (average waiting time = 46 ms) while waiting for the log file write Parallels is very good (average waiting time is less than 1 millisecond).

  The application is of type middleware, it connects to several other applications. A single user in a single application action train several requests to send back through this middleware, so he needs response time of db in milliseconds.

  The database is quite simple:

  -It has a few config tables that the application reads but rarely updated

  -She has table TRANSACTION_HISTORY: the application inserts records into this table using Insert einreihig (about 100 lines per second); each insert is followed by a validation.

  Records are kept for several months and then purged. The table has only column VARCHAR2/NUMBER/DATE, no LOBS, LONG, etc. The table has 4 non-unique single-column index.

  The average line length is 100 bytes.

  The load profile does not appear something unusual, the main figures: 110 transactions per second average transaction = 1.5 KB size.

  The data below are to 1 hour interval (purge wasn't running during this interval), physical reads or writes physical rate is low:

  Load profile

  ~ ~ ~ Per second per Transaction

  ---------------       ---------------

  Size: 160,164.75 1,448.42

  Logical reads: 521,58 57 675,25

  Block changes: 934,90 8.45

  Physical reads: 76,27 0.69

  Physical writings: 86,10 0.78

  Calls of the user: 491,69 4.45

  Analysis: 321,24 2.91

  Hard analysis: 0.09 0.00

  Kinds: 126.96 1.15

  Logons: 0.06 0.00

  Runs: 17.70 1 956,91

  Operations: 110,58

  
  

  Top 5 events are dominated by the synchronization of log file:

  Top 5 timed events

  ~~~~~~~~~~~~~~~~~~                                                     % Total

  Event expects Ela time (s)

  -------------------------------------------- ------------ ----------- --------

  401 608 18 448 59.94 file synchronization log

  db file parallel write 124 044 3 404 11.06

  CPU time                                                        3,097    10.06

  Enqueue 10 476 2 916 9.48

  DB file sequential read 261 947 2 435 7.91

  
  

  Section events:
  

  AVG

  Total wait wait wait

  Hour of wait time wait for the event (s) (ms) /txn

  ---------------------------- ------------ ---------- ---------- ------ --------

  Synchronize 0 401 608 46 18 448 1.0 file log

  db file parallel write 124 044 0 3 404 27 0.3

  Enqueue 10 476 277 2 916 278 0.0

  DB file sequential read 261 947 0 2 435 9 0.7

  buffer busy waits 11 467 67 173 15 0.0

  SQL * Net more data to the client 1 565 619 0 79 0 3.9

  lock row cache 2 800 0 52 18 0.0

  control file parallel write 1 294 0 45 35 0,0

  Log end of switch file 261 0 36 138 0.0

  latch free 2 087 1 446 24 12 0.0

  PL/SQL 1 1 20 19531 0,0 lock timer

  log file parallel write 0 143 739 17 0.4 0

  db file scattered read 1 644 0 17 10 0.0

  sequential log file read 636 0 8 13 0.0

  
  

  Log buffer is about 1.3 MB. We could increase the log buffer, but there is no log buffer space waits, so I doubt this will help.

  
  

  Newspapers in recovery have their own file systems, not shared with the data files. This explains the difference between waiting avg on parallel writing of log (less than 1 ms) file and db file parallel write (27 ms).

  Restoring logs is 100 MB, there are about 120 journal switches per day.

  
  

  What has changed: the pads/validations rate grew. Several months ago there were 25 inserts/validations per second in the TRANSACTION_HISTORY table, now get us 110 inserts/validation per second.

  
  

  What problem it causes application: due to slow down the reaction of the basis of the application (Java-based) requires discussions more and more.

  
  

  MOS documents on synchronization of log file (for example, 1376916,1 waits for troubleshooting "log file sync") recommend to compare the average waiting time on synchronization of log file and the log file parallel write.

  If the values are close (for example log file sync = 20 ms and log file parallel write = 10 ms) so expectations are caused by nits IO. However, it is not the case here.

  
  

  There was a bug (2669566) in 9.2 which resulted in underreporting lgwr parallel time of writing to the log file. I was talking about September 2005, during which the bug was present in 9.2.0.6, reported 10.1 fixed in: file parallel journal written (JL Comp) it is possible that your problem IS written to the log file.

  Concerning

  Jonathan Lewis

• "redo the write time" includes "log file parallel write".

  IO performance Guru Christian said in his blog:
  
  http://christianbilien.WordPress.com/2008/02/12/the-%E2%80%9Clog-file-sync%E2%80%9D-wait-event-is-not-always-spent-waiting-for-an-IO/
  
  Waiting for synchronization of log file can be divided into:
  1. the 'writing time again': this is the total elapsed time of the writing of the redo log buffer in the log during recovery (in centisecondes).
  2. the 'parallel log writing' is actually the time for the e/s of journal writing complete
  3. the LGWR may have some post processing to do, signals, then the foreground process on hold that Scripture is complete. The foreground process is finally awake upward by the dispatcher of system. This completes pending "journal of file synchronization.
  
  In his mind, there is no overlap between "redo write time" and "log file parallel write.
  
  But in the metalink 34592.1:
  
  Waiting for synchronization of log file may be broken down into the following:
  1 awakening LGWR if idle
  2 LGWR gathers again to be written and issue the e/s
  3. the time for the IO journal writing complete
  4 LGWR I/O post processing
  ...
  
  Notes on adjustment according to log file sync component breakdown above:
  Steps 2 and 3 are accumulated in the statistic "redo write time". (that is found in the SEO Title Statspack and AWR)
  Step 3 is the wait event "log file parallel write. (Note.34583.1: "log file parallel write" reference Note :) )
  
  MetaLink said there is overlap as "remake the writing time" include steps 2 and and "log file parallel write" don't understand step 3, so time to "log file parallel write" is only part of the time of 'redo write time. Won't the metalink note, or I missed something?
  

• transactions in rollback segments table

  Hi guys,.
  
  I read the following, but I'm still having a bit of difficulty to conceptualize. Someone would be so kind to give me a very brief example?
  
  Thank you
  
  For each rollback segment, Oracle maintains a table of transaction - a list of all transactions that use the associated rollback segment and entries of restoration for each change made by these operations.

  Whenever the transaction happens, there is an entry that is maintained by oracle to control that in which the segment, in which block cancellation of the transaction is maintained. The table which is now it is called Transaction table. The transaction entry is maintained for giving this information of cancellation for queries that seek when you need for coherent picture playback. Location of corresponding cancellation information are also maintained in the header of the block also Transaction as cancel Byte Address (UBA).

  The operating table is for us, V$ transaction. If you look at the XIDUSN, XIDSLOT, XIDSQN columns in this table, you would be able to see the segment where the cancellation of the transaction is maintained. Fixed to cancel arrays are x$ ktuxe and x$ ktcxb (hopefully, I did not error in names).

  I'll see if I can find good paper describing this.
  Update:

  Here are two links that I hope will be useful.
  http://www.evdbt.com/AutomaticUndoInternals.PDF
  http://www.juliandyke.com/presentations/RedoInternals.pp

  Do a lot of block of dumping, a very good way to know this stuff.
  HTH
  Aman...

  Published by: Aman... on March 10, 2009 01:10

• Transaction is written to the log file and it is not written to undo tablespace. During a failure of the system how oracle rolls back the transaction.

  Hi all

  My question is:

  Transaction is written to the log file and it is not written to undo tablespace.

  During a failure of the system how oracle rolls back the transaction.

  I have already provided the answer, you ignored if well (you seem to only read the responses by people of your country).

  Redo log is always written * first * before * writing to the data block (redo log writing is much more aggressive). So it DOESN 'T MATTER if you lose these scriptures of rollback segment.

  Valuation: rear roller followed by roll forward, using redo log files and/or archive redo log files.

  Sybrand Bakker

  Senior Oracle DBA

• data containing rollback segment file crashed

  Hello
  In one of our production box (oracle 8.1.7.4 and HP UX), data file that contains the rollback segment has crashed. To open the database, I commented the line segments rollback in init file and launched the db and submitted offline for a fall as the data file crashed
  
  ALTER database datafile ' / db10/rollback/rbs01.dbf' drop offline;
  
  and then I tried to drop the tablespace containing only datafile, but it threw an error indicating a rollback segment active R0 is always there in the tablespace. I do not know how to file the and create rollback segments. Any help would be greatly appreciated.
  
  
  Thank you
  Guna

  If the rollback segments are active, they are necessary to achieve the recovery process (roll forward was OK if you do not lose the redo, but there is a rolling back phase: read my previous post). Your database is probably not in very good condition.
  Can you post the last 50-100 lines of your alert.log?
  You have a valid backup of this data file?

• difference between roll back and the rollback segment.

  Hello
  
  
  10.2.0.1.0 Oracle
  
  What is the difference between reverse and cancel segemnt? they are an and even according to the change of version of oracle? Help, please

  Hello

  The two become the same functionality, but in oracle 9i they did simplify, because if you use rollback segments, you need to put them online in init.ora, and you must take care of management of space etc..
  so, they introduced in oracle 9i, tablespace undo you can creage undo segments and space management will take care of oracle managed files, so its reduced the load of s/n

  Kind regards
  Simma...