Quality of the data buffer Cache

Similar Questions

• LMD are in the DB buffer Cache?

  DB version: 11.2.0.4

  OS: RHEL 6.5

  Oracle documentation defines "database buffer cache" in the following way

  "The buffer of database cache, also called the buffer cache, is the area of memory that stores copies of data in blocks to read data files"

  http://docs.Oracle.com/CD/E25054_01/server.1111/e25789/memory.htm#i10221

  Let's say that the following UPDATE statement updates 100,000 records. The server process go get all the blocks that has the matching records and place it in the DB buffer cache and updates the blocks. This change metadata are recorded in the restore log buffer by progression. At the next checkpoint changed blocks are written to the data files. Right?

  Employee UPDATE

  SET salary = salary * 1.05

  The EMPLOYEE

  WHERE deptnum = 8;

  basically: Yes, once again. Oracle has rewritten Sales buffers (i.e. buffers with different content than the corresponding blocks on the disk) on the drive under certain conditions. If the operation is cancelled, the blocks must be read again in the cache and change must be cancelled (and written).

• CKPTQ in the database buffer cache and LRU

  Hi experts
  
  
  This feature can settle in cache buffers data base Oracle 10.2 or higher.
  Forums of sources: OTN and 11.2 Concepts guide
  
  According to my readings. To improve the functionality and make it more good American cache database is divided into several zones which are called workareasNow more
  
  Zoom this each activities will store multiple lists to store tampons inside the database buffer cache.
  
  Each wrokarea can have one or more then one lists to keep the wrokordering in there. The list of what each activity will have therefore to list LRU and list CKPTQ. LRU list
  
  is a list of buffers pinned, free and sales and CKPTQ is a list of stamp Sales. We can say THAT CKPTQ is a group of stamps Sales ordering of RBA weak and ready to be flushed from the cache on the disk.
  
  CKPTQ list is maintained by ordering of low RBE.
  As novice let me clearly low RBA and RBA senior first
  
  RBA is stored in the header of the block and we will give the information on which this block is spent and how many times it is changed.
  
  Low RBE: low RBE is the address to redo the first change that was applied to the block since his own last.
  RBA high: the high RBA is the address to redo the last change has been applied to the block.
  
  Now back to CKPTQ
  It can be like this (pathetic CKPTQ diagram)
  
  lowRBA = high RBA
  (Head of the CKPTQ)                         (CKPTQ line)
  
  CKPTQ is a list of stamp Sales. According to the concept of the RBA. The most recent modified buffer is at the tail of CKPTQ.
  
  Now the oracle process starts and try to get the DB cache buffer if she gets a buffer it will put an end SRM to the list.and buffer buffer LRU will become the most
  
  recently used.
  
  Now, if the process cannot find a necessary buffer.then first, he will try to find free tampons to LRU. If he finds his most he will place a datablock to the data file in the
  
  place where free buffer was sitting. (Good enough).
  
  Now, if the process cant fnd a buffer without LRU then first step would be he will find some Sales swabs at the end of the LRU to LRU list and place them on a
  
  CKPTQ (do not forget in the low order of RBA he organize it queue of CKPT). and now the oracle process will buffer required and place it on the end of the MRU of LRU list. (Because space was acclaimed by the displacement of Sales to CKPTQ buffers).
  
  I do not know of CKPTQ buffers (to be more precise tampon Sales) will move to datafiles.all buffers are line up n lower CKPTQ RBA way first. But
  
  emptied to datafile how and in what way and to what event?
  
  That's what I understand after these last three days, flipping through the blogs, forums and concepts guide. Now miss me you please erase me on and off it
  
  I can't bind the following features at this rate... It's
  
  (1) how the work of additional checkpoint with this CKPTQ?
  
  (2) now, what is this 3 second delay?
  
  (Every 3 seconds DBWR process will wake and find if nothing to write about the data files for this DBWR will check only CKPTQ).
  
  Apartment 3) form 3 second funda, when CKPTQ buffers will be moved? (IS IT when the process is unable to find any space in CKPTQ to keep buffers LRU. Its a
  
  moment where CKPTQ buffer will be moved on the disk)
  
  (4) can you please report when the control file will be updated with checkpoint so it can reduce recovery time?
  
  In many ques but I'm trying to build the entire process in mind that its operation may be I can be wrong in any phase in any stage, please correct me upward and
  
  Take me @ the end of the flow.
  
  
  Thank you
  Philippe

  Hi Aman,

  Yes, I a soft copy of ppt or white paper "Harald van Breederode" of 2009.

  -Pavan Kumar N

• clarification of term required for the DB buffer Cache

  Hello!!
  
  Here, I have a very basic conceptual question, DB buffer Cache contains the data read from the data in the file as well reduce the disk i/o of fom and oracle. If suppose that the table is constantly questioned and remains in the DB buffer cache all the time, how does oracle ensures the user gets the latest information?

  The database buffer cache is a part of the zone system Global (SGA), which is responsible for caching of blocks accessed frequently for a segment. The subsequent transactions involving the same blocks can then access them from memory, instead of from the hard disk. The works of cache buffer of database on the basis of least recently used (LRU algorithm), according to which the most frequently accessed blocks are kept in memory while the less frequent are gradually.

  See this link

  http://www.Stanford.edu/dept/ITSS/docs/Oracle/10G/server.101/b10743/memory.htm :)

• What else are stored in the database buffer cache?

  What else are stored in the database buffer cache, except the data reading of data files blocks?

  The nitty gritty on this point, you ask someone smarter than me waaay.

• Checking the quality of the data in the migration process

  Hi all
  
  I am in a project data migration from SQL Server for the Oracle database. But my question isn't running without the control of the quality of the data.
  
  My procedures to move data is: a) extract data in a flat file of SQLserver via an interface graphic tool) b ftp to UNIX c) sqlldr to Oracle temp tables d) copy data from temp tables for the fact tables.
  
  My point is to check the SQL Server log file and the file of log sqlldr, if no error in them and the match of counties line in SQL Server and Oracle, then we can say a, b, c are successful.
  
  And d a third party stored procedure, we can trust his straightness. I don't see any place where the error may occur.
  
  But the QA team think that we do a check over at least two: 1. compare some lines 2 column-by-column. the sum of the numeric columns in order to compare the results.
  
  Can anyone give me any suggestions on how to check the quality of the data in your migration projects, please?
  
  Best regards
  Leon

  Without wishing to repeat what has already been said by Kim and Frank that this is exactly the kind of thing you need controls autour.

  1. SQL Server export to a CSV file

  Potential of loose accuracy in data types, such as numbers, dates, timestamps, or character sets (unicode, utf, etc.)

  2 pass from windows to unix

  Immediately, there are differences in end of LIFE characters
  Potential differences in character sets
  Potential problems with incomplete ftp of files

  3 CSV into temporary tables with SQL Loader

  Potential of loose accuracy in data types, such as numbers, dates, timestamps, or character sets (unicode, utf, etc.)
  Potentail for control files do not catering for special characters

  4 copy temporary tables to fact tables

  May have bad column mappings
  Potential of loose accuracy in data types, such as numbers, dates, timestamps, or character sets (unicode, utf, etc.)

  And I don't know there are a lot of other things that could go wrong at any time. You must answer not only to the things wrong in the sense of disaster or disk falls into failure, network failure, precision of the lost information, but also consider that it might be obscure bug in one of the technologies that you are handling. They are not things you can predict directly, but you should have check in place to make sure you know if something went wrong - however subtle.

  HTH

  David

• question about the quality of the data and CKM

  If I understand correctly, CKM only supports the audit based on the constraints of the db. If I want to have more complicated built with the audit of the business logic, is the quality of the data as a good choice. Or any other suggestions?
  
  In my case, I'll have to check the data in the source table, based on the data in the table from different sources (the source and target tables). This should be doable thanks to the quality of the data, correct? I am new to ODI. When I first installed the ODI, I chose not to install the module of data quality. I guess I can install DQ separately and bind it to ODI? They share the same master repository?
  
  Sorry for the naïve questions, your help is greatly appreciated.
  
  -Wei

  Hi Wei,

  Not necessarily.

  You can create you own constraint that will only exist in ODI and can be complex.

  Right-click on "Constraints" in any data store, and you can navigate between them...

  This help you?

• Read data larger than the DB buffer Cache

  DB version: 10.2.0.4
  OS: Solarit 5.10
  
  
  We have a DB with 1 GB for DB_CACHE_SIZE. Automatic shared memory management is disabled (SGA_TARGET = 0).
  
  If a query is triggered on a table that will grab the 2 GB of data. Hang in this session? How oracle handles this?

  Tom wrote:
  If the recovered blocks get automatically removed from the buffer cache once it is retrieved by the LRU algorithm, then Oracle must handle this without any problem. Right?

  Yes. No problem in that the "+ a fetch size +" (for example, by selecting 2 GB with a value of lines) need to fit completely in the db (only 1 GB in size) buffer cache.

  As mentioned Sybrand - everything in this case is emptied as blocks of data more recent will be read... and that emptied shortly after thereafter as of the even more recent data blocks are read.

  The ratio / access to the cache will be low.

  But this will not cause Oracle errors or problems - simply that degrade performance as volumes of data being processed exceeds the capacity of the cache.

  It's like running a very broad program that requires more RAM which is available on a PC. The 'additional RAM' is the file on the disk. The APA will be slow because its memory pages (some disk) must be swapped in and out of memory as needed. It will work faster if the PC has an enough RAM. However, the o/s is designed to address this exact situation that requires more RAM than physically available.

  Similar situation with the treatment of large chunks of data than the buffer cache has a capacity of.

• The data buffer series before transmitting

  Hello, I'm relatively new to LabVIEW and had a question about how buffer data to the serial port before transmitting. I've attached what I have so far for a VI, and that's how I expected to work.

  1. Read in hexadecimal string (example: 001122334455)
  2. For loop repeats for half the length of the chain because I am transmitting into blocks of size bytes (example: 6F)
  3. Read the first byte of the ascii string and converts it to hexadecimal equivalent byte and transmits.
  4. Repeats until the chain is completed.

  Basically, I need to place a buffer that fills up my time loop ends then all the data at once. At the moment there is enough of delays between each loop causes errors.

  Any suggestions?

  everettpattison wrote:

  Basically, I need to place a buffer that fills up my time loop ends then all the data at once. At the moment there is enough of delays between each loop causes errors.

  Do you mean the while loop or loop for? In the picture, you put the note that you need a buffer inside the loop for, loop not quite awhile. The amount of calculations going on inside this loop is so small that I can't imagine how it is at the origin of the delays, but you can easily replace it to transmit an entire string at a time. Put Scripture VISA outside the loop for. wire the output channel of the conversion at the border of the loop for, creating a tunnel. Connect the output of this tunnel to concatenate strings, which will combine an array of strings into a single string. Then connect to the entry VISA.

  EDIT: even better, get rid of the conversion, the U8 to wire directly for the edge of the loop, use the byte array to a string to be converted to a string, send this string to Write VISA. There is probably an even easier approach, but I'm not looking too carefully.

• What did you do to increase the quality of the data?

  Hi all

  We are looking to hire a vendor to help with a record increase completeness and we help build of data overall quality best practices. For example, a lot of our data fields are empty, but our forms are not hosted in Eloqua so it is a more complicated solution. What did your business in situations like this? Have you worked with any organization of data services truly stellar? Any advice or suggestions are welcome!

  Hi Hayley,

  We work with many customers on that sort of thing.  I would recommend a number of things:

  1. review how you can exploit existing data sources, there are mentions in this thread on the internal data warehouse, etc. and even how you host your forms on the outside.  So understand what you have internally that you can use the data sources (and confidence) to fill the gaps.

  2. If you plan to use a data adding to the seller (and there are many choices), to understand what makes sense for you.  It is a complete database add? Something that someone like D & B, ReachForce or NetProspex can offer you.  Or is it to get more data on people who submit your forms (and a solution such as ReachForce SmartForms or DemandBase)? Or is it two?  Determine what is important and where you can get information, as well as the best strategy to ensure that you get the biggest bang for your money.

  3. build processes within Eloqua to bring it all together.  Create standardized values, Eloqua allows to align the data you get these values and make sure that your segmentation, lead scoring programs and programs are aligned accordingly.

  Also don't forget, once you have all that in Eloqua how do you share it in your CRM?

  Hope this helps, feel free to DM me if you have any specific questions.

  Best,

  Lauren

• about the data dictionary cache

  Can someone explain this statement?
  
  "Large OLTP systems where users connect to the basis of their own user ID can explicitly benefit the owner of qualifying segment, rather than using public synonyms. This greatly reduces the number of entries in the dictionary cache. »
  
  Thanks in advance

  Claire wrote:
  http://psoug.org/reference/synonyms.html

  concerning

  Yes, the statement is quite right but doesn't explain it well. I did a search and find Tom had discussion on it and claim the same. See the answer

  On a small test, with one user, you can count the latch accesses and see significant differences
  that may not appear to be terribly threatening . But with large numbers of users, the number of
  'clones' of objects with the same name in the same namespace and therefore on the same latch, goes
  up, and the time taken to search a chain can become a serious threat if everyone is trying to
  access some information about their verion of the 'same' object.  The scale of the problem is order
  n-squared with respect to the number of different users.
  

  Tom reviews the issue of scalability using the public synonym. As the number of users increases it would have more cloned copies Similarly, and they would be protected under lock and key, if of locking issues. I'll nedopil my previous post so that others don't get confused. And it was a kind of larning for me as well. Thanks for asking this question.

  Link - http://asktom.oracle.com/pls/asktom/f?p=100:11:0:P11_QUESTION_ID:7555433442177 #7640980652786

• Updated data are larger than the buffer cache

  Hi Experts,

  I have a small request. I have a table called CONTENT to have 12 GB of data. Here, I pulled a single update statement that updates to 8 GB of CONTENTS table of data using 1 GB of database buffer cache?

  How 1 GB of the Database Buffer Cache will be used to update the 8 GB of data? Level architectural any additional changes will happen (than usual) when executing "Updated data is larger than the buffer cache"?

  Could someone of you please response. Thank you

  Database: 10.2.0.5

  OS: Power 5-64 bit AIX system

  Hello

  the basic mechanism is the following:

  needed to update data blocks are read from the data files and cached in memory (buffer cache), the update is made to the buffer cache and the front of the (UNDO) image is stored in the segments of cancellation, operation (update here) is re-encoded to redo buffer until it goes again files If the buffer is samll or we need more space in the buffer cache, or we have a control point or... Oracle writes back the block modified data files to free the memory buffer for the more blocks.

  While the other runs the update of transactions can read before you change the image of CANCEL if validation, at the end of the transaction done change is confirmed and validation is recorded in the redo. If the cancellation is made at the end of the transaction before the image is "restored" and rollback is saved in do it again.

  Concerning

• Changing data in the undo tablespace or db Oracle buffer cache

  Hello
  
  I have serious doubt in the feature of oracle architecture, when a user issues an update statement, the data blocks are transported to the db buffer cache and where the data changes are made? Made a copy data block is stored in the cache db pads and the changes are made to the block in the buffer cache? or the copy of the data block is stored in the undo tablespace and changes are made to the blocks in the undo tablespace?
  
  In singles, the changes to the data blocks are make to the db or undo tablespace buffer cache?
  
  
  Thanks in advance
  
  Kind regards
  007

  Did you have a look to the Internet for the answer?

  In short, if a trial Oracle wants to update a record in the table, it does:

  -Read the record to be changed in the buffercache
  -Audits (the record already locked, is the update allowed)
  -Put the folder (called image before) in a rollback in the UNDO tablespace segment
  -Writing redo information about this change in the UNDO tablespace
  -Lock the record
  -Write the change in registration in the buffer cache
  -Put the change also in the redo buffer
  S ' sit and wait... (for a commit or a rollback)

  When are committed:
  -Release the lock
  -Empty folder of restoration since the UNDO tablespace
  -Write a record of this change forward in the UNDO tablespace

  When rollback:
  -Release the lock
  -Rinse the record changed the buffercache
  -Read the original value
  -Empty folder of restoration since the UNDO tablespace
  -Write a record of this change forward in the UNDO tablespace

  It of here, some more specific complexity when a checkpoint occurs between the change and the commit / rollback or redo buffer has been emptied for redo files

  Please any other s/n, correct me if I'm wrong...

  See you soon
  FJFranken

• Buckets of the interaction between the physical i/o and buffer cache hach

  I read the book Expert Oracle practices on issues of lock contention. While I was reading this chapter. I'm little bit confused the bahavior of the buffer cache when physical i/o occurs. According to Tom Kyte, when data blocks are read on disk (if missed cache) the following steps occurred. Ask Tom & amp; quot; How to work the Database Buffer Cache? & amp; quot;

  (a) access to the buffer cache and search for block

  (b) if the block isn't here, perform physical i/o and put it in the cache

  (c) return the block of memory cache

  However, I wonder what stage b has occurred which means put the data block in the buffer cache. For this, the data block is added to the associated buffer cache hash buckets?

  As far as I know, in order to cache data hit intended address of applicable block in buffer cache hash bucket. The hash function is generated during this data block address. (if acquired the lock of the child) And then find the address of the data block in the cache buffer chain to locate the block of buffer in the buffer cache.

  My second question is what stage an occur (go to the buffer cache and search block) how to block oracle look? I mean where did he look like? My third question relates to my second question, Oracle if discovered that the block in the buffer cache, does know where to find them? I guess that Oracle does not know where to locate it in the buffer cache. Therefore, it uses cache buffer hash buckets. I'm wrong?

  Last question is, I'm just trying to understand how buffer cache buffers are linked, buffer cache buffer hash, how it works?

  Thanks in advance.

  > What happens if planned lines resident for other blocks of data in the table? How can you join the other data block addresses? And, how do you know that lines which are located in what block of data?

  See this demo:

  Microsoft Windows XP [Version 5.1.2600]

  Copyright (C) 1985-2001 Microsoft Corp.

  C:\Documents and Settings\Administrateur > sqlplus scott/tiger

  SQL * more: Production release 11.2.0.1.0 Wed Dec 18 09:01:50 2013

  Copyright (c) 1982, 2010, Oracle.  All rights reserved.

  Connected to:

  Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production

  With partitioning, OLAP, Data Mining and Real Application Testing options

  SQL > drop table test is serving;

  Deleted table.

  SQL > create table test in select * from object;

  Table created.

  SQL > set line 200.

  SQL > column nom_segment for a20;

  SQL > select nom_segment, segment_type, header_file, header_block dba_segments where nom_segment like 'TEST '.

  NOM_SEGMENT SEGMENT_TYPE HEADER_FILE, HEADER_BLOCK

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

  4 1218 TEST TABLE

  Average for test table header block are 1218 that resides in file number 4.

  SQL > SELECT

  2 dbms_rowid.rowid_relative_fno (rowid) REL_FNO,

  3 dbms_rowid.rowid_block_number (rowid) BLOCKNO

  4 test where object_name = 'EMP ';

  REL_FNO BLOCKNO

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

  4 2443

  SQL > variable s/n varchar2 (30)

  SQL > exec: s/n: = dbms_utility.make_data_block_address (4, 2443);

  PL/SQL procedure successfully completed.

  SQL > print s/n

  S/N

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

  16779659

  SQL > SELECT

  2 dbms_rowid.rowid_relative_fno (rowid) REL_FNO,

  3 dbms_rowid.rowid_block_number (rowid) BLOCKNO

  4 test where object_name = 'I_AUDIT ';

  REL_FNO BLOCKNO

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

  4 1223

  SQL > exec: s/n: = dbms_utility.make_data_block_address (4, 1223);

  PL/SQL procedure successfully completed.

  SQL > print s/n

  S/N

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

  16778439

  SQL >

  Then, I got two dBA for different lines that are in the block No. 2443 and 1223.

  Concerning

  Girish Sharma

• Write the list of database buffer Cache

  What is the list of write in the database buffer cache? What is he function?
  
  Thanks in advance.

  >
  What is the list of write in the database buffer cache? What is he function?
  >
  The list of writing to dirty buffers that have not been written to disk yet.

  See "Database Buffer Cache" in the Concepts of database 11g doc
  http://docs.Oracle.com/CD/B28359_01/server.111/b28318/memory.htm
  >
  Organization of the Database Buffer Cache

  The buffers in the cache are organized into two lists: list of Scripture and the list (LRU) least recently used. List of writing contains stamps Sales, but which contain data has changed, has not yet been written to disk. The LRU list holds free buffers, pinned buffers and dirty buffers that have not yet moved to the list of Scripture. Free buffers contain no useful data and can be used. Pinned buffers are being accessed.