relationship between redo log buffer, journal of redo and undo tablespace files

Similar Questions

• Difference between redo logfiles, Undo Tablespace, Archive log data file

  Can some please highlight the difference between Undo and Redo Logs
  Also why we need to separate the archive logs when the recovery log data can be written directly in data files...
  
  Help you will be highly appreciated...

  Hello

  Ed gave you a very good answer.

  Rememeber database files are online and they are written to by DBWR process. So we have the database files, redo log files and archive logs.
  In order to avoid all the crawl log when you perform a recovery, database performs control points that summarize the State of the database. This operation of control point provides a shortcut to the recovery. At the checkpoint, the database knows that all incorrect pages were written to disk (for example, database files). At the time of recovery, the log (which includes-finished and unfinished transactions) is used to bring the database to a consistent state. The system locates the time of the last checkpoint and returned to this position in the log file. Then he restores forward all completed transactions (read committed) that occurred after the last checkpoint and rolls back all transactions that were not committed, but that began before the last checkpoint. This is where online log files are used.

  Now imagine that you need to back up your database GB 100 + all 10 minutes. It would be a waste of space! So you take a backup of your database at time t and backups of archiver process redo logs periodically to check the newspapers so that redo log files can be replaced and RMAN will use the last backup and archive the log files to recover your database at the time.

  Now, I mentioned the checkpoint process. The Checkpoint process regularly launches a control point that uses DBWR to rewrite all the blocks Sales in the data files, so synchronize the database. Imagine one dam is running and have exhausted all the redo log files. At this point, Oracle will wait until all Sales already queued blocks have been written to the buffer on disk (database files) foremost him redo log files can be considered as superfluous and available for re-use (i.e. can be overwritten). This will result in the following message in the alert.log:

  Thread 1 advanced to log sequence 17973
    Current log# 3 seq# 17973 mem# 0: /oracle/data/HAM1/log3aHAM1.dbf
    Current log# 3 seq# 17973 mem# 1: /oracle/data/HAM1/log3bHAM1.dbf
  Thread 1 cannot allocate new log, sequence 17974
  Checkpoint not complete
    Current log# 3 seq# 17973 mem# 0: /oracle/data/HAM1/log3aHAM1.dbf
    Current log# 3 seq# 17973 mem# 1: /oracle/data/HAM1/log3bHAM1.dbf
  Thread 1 advanced to log sequence 17974
  

  I am sure you have done the following:

  alter database mount;
  
  Database altered.
  

  When you mount a database, Oracle combines the instance started the database. Oracle control files are opened and read. However, no checking such as the restore/recovery is performed

  alter database open;
  
  Database altered.
  

  An open command opens the data files, recovery logs, it performs automatic and consistency of database recovery. At this point, the database is now ready to be used by all valid users.

  HTH,

  Mich

  Published by: Mich Talebzadeh on November 19, 2011 16:57

• Redo and undo logs

  Hello
  
  I have an application that uses oracle 10 g 2. This is on Linux x84_64.
  
  I want to know "the amount of ' redo and undo logs the application generates.
  
  Can you please tell me on how to do this?
  
  Is there a way where I can tell that the log redo and undo log until the application started x and after the application finished the redo and undo is now 'y '?
  
  -Kiss

  Query v$ mystat would show only for your current session. Once you disconnect and connect again, the session id is different. Also, of course, it does not display data for other sessions.

  If you want statistics database instance level, you should be questioning for "size" in v$ sysstat. This view shows the statistics accumulated since the restart of the database instance. To identify the differential redo generated within a specified period, you will need to take snapshots of size "remake" at the beginning and at the end of the fixed period. If you use StatsPack or AWR (which requires the License Pack diagnosis), the reports generated by these packages also see again you generated during a period (for specified snapshots).

  Information on the cancellation rate is available from v$ undostat.

  Hemant K Collette
  http://hemantoracledba.blogspot.com

• What are the relationships between the logging and IKM?

  What is the best method to use in the following scenario:
  I have about 20 tables with the large amount of data sources.
  I need to create interfaces that join the source tables in target tables.
  The tables are inserted every few seconds with about hundreds of thousands lines.
  There may be a gap of a few seconds between the insertion of different tables that could be attached.
  The source and target tables are on the same Oracle instance and schema.
  I want to understand the role of: 'Logging CDC' and "IKM - incremental" and
  How can I use it in my script?
  In general, what are the relationships between "Logging" and 'IKM '?
  Use both? Or maybe it's better deelte and insert the target tables?
  
  I want to understand what is the role of "Logging CDC"?
  Can 'IKM - incremental' work without "logging"?
  Must 'Logging' have PK on the tables?
  What should I do if I can't say PK (there may be several identical lines)?
  
  Yael thanks in advance

  user604062 wrote:
  Hello
  Thanks for your quick response!

  No probs - its still fresh in memory I did a major project on this topic last year (400 tables, millions of lines per day (inserts, updates, deletes), sup-5 minute latency). The problem is it isn't that well written on the web, that you have read the blog of the example I linked to in my first answer? See also here: http://odiexperts.com/changed-data-capture-cdc/

  Always on logging:
  My source table is inserted all the time.
  The interface to join the source table in the target table.

  In ODI, the correct term would be your source table "fits" in the table target, unless you mean literally that want to join the the source with the taget table table? My question if you want to do with the result of the join?

  What exactly the "journaling" CDC updates?
  It updates the model of ODI? interfaces? The source of data in the model of ODI? The target table?

  Logging CDC configures and deploys the data capture mechanism (Triggers or log based capture, IE Logminer/streams/Goldengate) - it is not updated the model as such, she pointed out the metadata of the model of ODI repositoty as a CDC data store, allowing you, the developer say ODI to use log data if you wish (reported in the interface) There is no change in the target table, you get an indicator of metadata (IND_UPD) against a line during the integration (in C$ and I have tables$) that tells you if its insertion (I) and update (U) or deletion (D). It had ' lines allow you to synchronize the deletions, but yoy say its inserts only then you probably used use this option. "
  So the only changes are the source table to your interface, another diary data (if you use logging) or the table of the actual source (if not using the logging).

  This is the main thing that I don't understand!

  I hope I made a little clearer.

  Try the following as a quick test:

  Reverse a source table an engineer and the target (at least) table.
  Import the update incremental LKM and IKM.
  Import of the JKM you want to use.

  Create an interface between the source and the target without any deployed JKM.
  Configure the options of JKM on the model, the "Start log" to start the process of capture - this is quite a complex stage and a lot of things to understand what is happening in the source database, better to check code ODI sends to the database and to review the documentation of Oracle database for a description of what his weight (instantiate Tables (, sets of creating change, creation of subscribers etc. establishment of newspaper groups, creating views Journalising etc.) -you will need to consult your Source DBA database initially as ODI wants to make many changes to the source DB (in mode Archivelog process max, parallelism, size, Java etc.)

  Now, edit your interface and mark the table source for use "Journalized data bank.
  Restart your interface
  Compare the difference in the generated code in the journal of the operator, see the differences of the operator.

  >

  Thank you, Yael

• Instance - Redo and Undo recovery question

  I'm a little confused about how to undo and redo used to restore, please help me to clarify this point. If redo records changes (validations and database changes to cancel the revenge), don't do it again and undo all come from the log to roll forward to instance recovery? What is the source of the undo data, do it again save or cancel the segments that have been rebuilt using recovery logs?
  
  Matt

  In simple terms:
  Source of redo - redo logs, source of cancellation - undo tablespace. Oracle applies again to the data files, including cancellations of TBS, first, then it restores the unvalidated data using TBS of cancellation.

• Relationship between the samples through the second rate and sampling

  I was wondering if someone could clarify the relationship between the samples through second rate and sampling.

  I have USB6008 and USB6363 of the tips that I work with in Measurement Studio.

  For the nec USB6008 entry differential (up to four channels of HAVE), if I put a sampling frequency to 8192 samples per second, and I updated 2048 samples per channel with:

  Task.Timing.ConfigureSampleClock ("", 8192, SampleClockActiveEdge.Rising, SampleQuantityMode.ContinuousSamples, 2048)

  Am I right in assuming that:

  • through the 4 analog inputs 8192 samples will be collected every second
  • 2048 samples will be taken by way of analog input for each scan
  • The time between two successive data points is 1/2048 seconds (about 0.5 ms)

  Hi DKIMZEY,

  The help page for the "Timing.ConfigureSampleClock method" should have a hypertext link to the page "Sample clock" in NOR-DAQmx help, that contains this text: "this sample clock sets the interval of time between samples. Each tick of the clock starts the acquisition or the generation of one sample per channel. "When the sample clock frequency is 8192, then the time between two successive data for a single channel is 1/8192 seconds. The time between the data points on two adjacent channels is controlled by the clock to convert, which can be controlled independently on most devices (up to a point).

  Brad

• How is the relationship between the IMEI number of a device and the e-mail ADDRESS provided by Blackberry?

  Hi all

  Is it possible to know what Blackberry device belongs to the BES server who? I m developing an application through which, I want to validate the email address by sending a device IMEI number.

  Is this possible? Show me the way...

  Thanks a lot for your information.

• Relationship between the contents of the toolbar custom and "Viewer".

  What link, if any, replica 'Viewer' icon in my other custom content? (Help, in this case my screen.)

  The Viewer icon is still present, but I would also like to have a button instead of something that says "click on the viewer below button to return."

  As much as I can say that we do not support a hyperlink to replicate what is the icon "Viewer". See Digital Publishing Suite help | Overlays of hypertext link and button for all locations of hyperlink that we support.

  Neil

• Redo Log Buffer - Online redo - archived journal - LGWR

  Hello
  
  It is specified in this document that redo entries is set to all changes (LMD), the database Redo Log Buffer (my question is when does? after validation?).
  
  And, in this connection, they say engaged and committed changes in the section again. But when you scroll down to the section Commit on the same link, after a commit log writer process (LGWR) will write journal entries of the SGA (log buffer) forward in the line redo log file.
  
  I wonder how? When I tested it on my database table that holds the record of > 300 000, recovery, and subsequently logs archive logs is generated (I did not commit the DML yet).
  
  Now my question is, how far is the whole of the archivelogs will be useful at the time of recovery, if I restore the changes? If Oracle doesn't know these archivelogs, why it should generate?
  
  And what section in the second link is correct?
  
  Help, please.
  
  Thank you
  Aswin.

  Aswin,

  Undo segments are ordinary data segments. Data segments are protected by roll forward. Temporary segments are not protected restore in progress.
  If in the case of an accident, when Oracle must retrieve a rollback segment, it will use again to recover this segment.
  In crash recovery, the first thing that will happen is rollback (Undo uncommitted changes), followed by rollforward ("readback" of committed changes).

  HTH

  -----------------
  Sybrand Bakker
  Senior Oracle DBA

• Redo Log Buffer 32.8 M, looks great?

  I just took on a database (mainly used for OLTP on 11 GR 1 matter) and I'm looking at the level of the log_buffer parameter on 34412032 (32.8 M). Not sure why it is so high.
  

  select 
      NAME, 
      VALUE
  from 
      SYS.V_$SYSSTAT
  where 
      NAME in ('redo buffer allocation retries', 'redo log space wait time');
  
  redo buffer allocation retries     185
  redo log space wait time          5180

  (database was for 7.5 days)
  
  Any advice on that? I normally keep trying to stay below 3 m and have not really seen it above 10 M.

  Sky13 wrote:
  I just took on a database (mainly used for OLTP on 11 GR 1 matter) and I'm looking at the level of the log_buffer parameter on 34412032 (32.8 M). Not sure why it is so high.

  11g, you should not set the log_buffer - only Oracle default set.

  The value is derived relative to the setting for the number of CPUS and the transaction parameter, which can be derived from sessions that can be derived processes. In addition, Oracle will allocate at least one granule (which can be 4, 8 MB, 16 MB, 64 MB, or 256 MB depending on the size of the SGA, then you are not likely to save memory by reducing the size of the log buffer.

  Here is a link to a discussion that shows you how to find out what is really behind this figure.
  Re: Archived redo log size more than online redo logs

  Concerning
  Jonathan Lewis
  http://jonathanlewis.WordPress.com
  Author: core Oracle

• REDO LOG BUFFER DOUBT

  Hi EXPERTS,
  
  IM on 11 G R2, RHEL 5 my question that when the data changes in the database buffer cache how immediately it is copied in the redo log buffer. I mean what process the copy. I read it in the oracle documentation only when waiting for event [log file command (private stream flush incomplete)] LGWR waits DBWR again complete flushing of buffers IMU in the recovery log buffer. Completion of DBWR LGWR can then finish writing the log in process and then move the log files.
  

• Question about the size of the redo log buffer

  Hello
  
  I am a student in Oracle and the book I use says that having a bigger than the buffer log by default, the size is a bad idea.
  
  It sets out the reasons for this are:
  
  >
  The problem is that when a statement COMMIT is issued, part of the batch validation means to write the contents of the buffer log for redo log to disk files. This entry occurs in real time, and if it is in progress, the session that issued the VALIDATION will be suspended.
  >
  
  I understand that if the redo log buffer is too large, memory is lost and in some cases could result in disk i/o.
  
  What I'm not clear on is, the book makes it sound as if a log buffer would cause additional or IO work. I would have thought that the amount of work or IO would be substantially the same (if not identical) because writing the buffer log for redo log files is based on the postings show and not the size of the buffer itself (or its satiety).
  
  Description of the book is misleading, or did I miss something important to have a larger than necessary log buffer?
  
  Thank you for your help,
  
  John.
  
  Published by: 440bx - 11 GR 2 on August 1st, 2010 09:05 - edited for formatting of the citation

  A commit evacuates everything that in the buffer redolog for redo log files.
  A redo log buffer contains the modified data.
  But this is not just commit who empty the redolog buffer to restore the log files.
  LGWR active every time that:
  (1) a validation occurs
  (2) when the redo log is 1/3 full
  (3) every 3 seconds
  It is not always necessary that this redolog file will contain validated data.
  If there is no commit after 3 seconds, redologfile would be bound to contain uncommitted data.

  Best,
  Wissem

• Redo log buffer question

  Hi master,
  
  This seems to be very basic, but I would like to know internal process.
  
  We know all that LGWR writes redo entries to redo logs on the disk online. on validation SCN is generated and the tag to the transaction. and LGWR writes this to online redo log files.
  
  but my question is, how these redo entries just redo log buffer? Look at all the necessary data are read from the cache of the server process buffers. It is modified it and committed. DBWR wrote this in files of data, but at what time, what process writes this committed transaction (I think again entry) in the log buffers cache?
  
  LGWR do that? What exactly happens internally?
  
  If you can please focus you some light on internals, I will be grateful...
  
  
  Thanks and greetings
  VD

  Vikrant,
  I will write less coz used pda. In general, this happens
  1. a calculation because how much space is required in the log buffer.
  2 server process acquires redo copy latch to mention some reco will be responsible.

  Redo allocation latch is used to allocate space.

  Redo allocation latch is provided after the space is released.

  Redo copy latch is used copy redo contained in the log buffer.

  Redo copy lock is released

  HTH
  Aman

• How do to the size of the log buffer reduce with huge Pages Linux

  Data sheet:

  Database: Oracle Standard Edition 11.2.0.4

  OS: Oracle Linux 6.5

  Processor: AMD Opteron

  Sockets: 2

  Carrots / power outlet: 16

  MEM: 252 GB

  Current SGA: GB 122 automatic shared memory (EAMA) management

  Special configuration: Linux huge Pages for 190 GB of memory with the page size of 2 MB.

  Special configuration II: The use of the LUKS encryption to all drives.

  Question:

  1. How can I reduce the size of the log buffer? Currently, it appears that 208 MB. I tried to use log_buffer, and it does not change a thing. I checked the granule size is 256 MB with the current size of the SGA.

  Reason to reduce:

  With the largest size of log buffer the file parallel write newspaper and the synchronization log file is averaged over 45 ms most of the time because she has dumped a lot of stuff at the same time.

  Post edited by: CsharpBsharp

  You have 32 processors and 252 GB of memory, so 168 private discussions, so 45 MB as the public threads size is not excessive.  My example came from a machine running Oracle 32-bit (as indicated by the size of 64 KB of threads private relative to the size of 128 KB of your son) private with (I think) 4 GB of RAM and 2 CPUs - so a much smaller scale.

  Your instance was almost inactive in the meantime so I'd probably look outside the Oracle - but verification of the OS Stats may be informative (is something outside the Oracle using a lot of CPU) and I would like to ask you a few questions about encrypted filesystems (LUKS).  It is always possible that there is an accounting error - I remember a version of Oracle who report sometimes in milliseconds while claiming to centisecondes - so I'll try to find a way to validate the log file parallel write time.

  Check the forum for any stats activity all over again (there are many in your version)

  Check the histogram to wait for additional log file writes event (and journal of file synchronization - the lack of EPA top 5 looks odd given the appearance of the LFPW and and the number of transactions and redo generated.)

  Check the log file to track writer for reports of slow writes

  Try to create a controlled test that might show whether or not write reported time is to trust (if you can safely repeat the same operation with extended follow-up enabled for the author of newspaper which would be a very good test of 30 minutes).

  My first impression (which would of course be carefully check) is that the numbers should not be approved.

  Concerning

  Jonathan Lewis

• Relationship between db_flashback_retention_target and fast_recovery_area

  Hi all
  
  I was doing a test on Flashback Database on my Oracle 11 g 2 and I would like to seek clarification on the relationship between db_flashback_retention_target and fast_recovery_area. Here is my current settings:
  
  
  SQL > show parameter db_flashback_retention
  
  VALUE OF TYPE NAME
  ------------------------------------ ----------- ------------------------------
  db_flashback_retention_target integer 60
  
  
  SQL > show parameter recovery_file_dest
  
  VALUE OF TYPE NAME
  ------------------------------------ ----------- ------------------------------
  db_recovery_file_dest string L:\app\amosleeyp\fast_recovery
  _area
  whole large db_recovery_file_dest_size 20G
  
  
  That is the question. I know that the db_flashback_retention_target parameter specifies the upper limit (in minutes) to how far back in time, the database can be flashed to the rear. I did a test and this is the sequence of events.
  
  REMOVE FROM SCOTT. EMP WHERE ename = 'KING '. -* 12:13
  FLASHBACK DATABASE IN TIME = ' TO_DATE ('2013-03-25 12:12 ',' YYYY-MM-DD HH24:MI:SS') "; -* 13:30
  Select count (*) Scott. EMP where ename = 'KING '. -* 13:31
  
  COUNT (*)
  ----------
  1
  
  This simple test, I have the database of flashback to more than 60 minutes there despite my window of retention being set at 60 minutes. That's the reason that I have a huge 20 G db_recovery_file_dest_size? So I can't go back in time for more than 60 minutes? Thanks for sharing.

  Hello

  So you mean that the target of retention may be about 59,60, 61minutes or more depending on the space of fast_recovery_area? So it actually fluctuates? ~

  No, it does not fluctuate. fast_recovery_area is just a storage area for versatile use for backup, backup, archived redo logs, and flashback logs etc, so do not confuse with retention of flashback.
  retention of flashback time is time that Oracle will always ensure you the flashback database. If set to 60 minutes, then you will certainly be able to flashback your database at least 60 minutes.
  If your fast recovery area is free, Oracle will not remove the flashback logs (and you might be able to flashback to even several days if flashback logs have not been removed from the quick recovery area). It removes only the flashback logs if fast recovery area a little space left in it.

  Only when I put guaranteed restore points, then it will store always on 60 minutes?

  See below for this concept

  http://docs.Oracle.com/CD/E11882_01/backup.112/e10642/flashdb.htm#autoId8

  Salman