I learnt that logWriter writes in the redo log files when redo log buffer is 1/3 full, it means that 66 % of redo log buffer are always empty and never used,
if no, isn't a waste of memory (66 % always empty !)
What's the difference between a dirty buffer and a redo buffer?
My understanding is that a dirty buffer is a changed buffer or whenever data changes in the buffer cache, it's marked as dirty. Also, a redo buffer keeps track of changes that were made to the data, so it's also referring to changed data as well...DWBn writes dirty buffers to disk and LGWR writes redo data to redo log filesHow can we differentiate between the two?
1)If i issue a DELETE statement to delete a row, will this statement drag any data from the datafile to database buffer? How is the change made by a DELETE statement recorded in buffer cache? How is this change then applied to the data in datafiles after commit?
View 7 Replies View RelatedHow can i know which objects used keep buffer cache?
View 5 Replies View RelatedSay Database Buffer Cache configured as 2M and my updates may use 4m size,will it throw an error message or update will happen perfectly without any issues?
View 2 Replies View RelatedI am in charge of several instances located on a Linux server CentOS, virtualized on a ESX 3.5 environment.
From time to time (every 4 to 5 days), I have some errors in the alert.log. Last occurence was last night :
Corrupt block relative dba: 0x01004e12 (file 4, block 19986)
Fractured block found during buffer read
Data in bad block:
type: 6 format: 2 rdba: 0x01004e12
last change scn: 0x0000.131aaa5b seq: 0x2 flg: 0x04
[Code] ........
We are doing user manual backup (with BEGIN/END BACKUP) every night at 8PM, ending at 9PM approx. Then, fractured blocks never occur during backups. At 1AM, the maintenance window is opening, thus explaining the GATHER_STATS_JOB job.
When I check corruption on early morning, I am always unable to reproduce the problem. DBV is OK without issues. We never had a problem with the data itself, whatever it is a table or an index in the reported failed block.
I would like to know what could cause these logical corruption, and how to stop them ?
I have oracle 9i running on HP-UX, I would like to find how much redo we are generating in a given period of time, is there any script that I can use to get this information?
View 3 Replies View RelatedI've a situation where I've very less redo logs generated. Let us say 10MB. Which solution will be better ?
1. Create one redo log group about 12 MB in size.
2. Create two redo log groups about 5 MB each in size as recommended by Oracle.
Even though solution 1 is also appropriate for me because I've less redo generated than the redo log group size. My whole redo will fit in this and I can raise checkpoint forcefully after certain period of time let us say every 3 seconds.
In one of our DB I found scenario one is implemented. So I want to know pros and cons of both of these practices.
I have some doubts about redo log files,
1) Can we fetch 'select statements' from redo log files through the use of log miner utility or any other?
(I think redo log file contains only insert,update,delete and DDL/DCL commands only)
2) If "No" to the above answer then how can i fetch all select statements fired on the system for a day or particular time.
(setting of sql_trace may be the one of them, but can it be possible for system level)
Today i noticed one problem with my database,my redologs switches in every 3mins,i also noticed there is no more transaction changes happening in database but still redo switches.
Fri Oct 05 06:10:05 2012
Thread 1 advanced to log sequence 79244
Current log# 2 seq# 79244 mem# 0: D:ORADATAORACIREDO02.LOG
Fri Oct 05 06:12:16 2012
Thread 1 advanced to log sequence 79245
Current log# 1 seq# 79245 mem# 0: D:ORADATAORACIREDO01.LOG
Fri Oct 05 06:14:28 2012
[code]......
why redo switch happening,any internal problem causes redo to switch .
redo generation. As I found the below statement in another forum."Undo segment generates the redo data also, because undo segment is database changes, so it generates the redo data also."
How a Undo segment can generate Redo and Undo datas.
Redo is getting generated very high. how to find out the reason ? database kept under 2 node cluster. chcked alert log trace and log writer trace files. pasted the content as below:
--alert log trace from node1 ( node2 also has same type of message ). Archive destination disk group - TXCOM_BACKUP_01 having enough space ( 80gb )
Mon Jan 7 00:49:10 2013
Thread 1 advanced to log sequence 448546 (LGWR switch)
Current log# 1 seq# 448546 mem# 0: +TXCOM_DATA_01/txcom/onlinelog/group_1.274.785770579
Current log# 1 seq# 448546 mem# 1: +TXCOM_DATA_01/txcom/onlinelog/group_1.302.802265189
Mon Jan 7 00:49:10 2013
[code]...
In the alert log, I am able to see the archive destination disk group ( TXCOM_BACKUP_01 ) is getting DISMOUNTED and again getting MOUNTED during every archive file generation. .
Mon Jan 7 00:49:20 2013
SUCCESS: diskgroup TXCOM_BACKUP_01 was mounted
SUCCESS: diskgroup TXCOM_BACKUP_01 was dismounted
SUCCESS: diskgroup TXCOM_BACKUP_01 was mounted
SUCCESS: diskgroup TXCOM_BACKUP_01 was dismounted
archive destination parameter in both nodes are not configured. it should read diskgroup name. ( +TXCOM_BACKUP_01 ) and corresponding size limit. Should i configure this ?
SQL> show parameter db_recovery
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
db_recovery_file_dest string
db_recovery_file_dest_size big integer 0
[code]...
should i bring the database to mount stage and set log_archive_max_proesses to high count ? now value is 2 ( default )
SQL> update t set a = 1 where b = 2; -- must have redo record
2 rows updated.
SQL> rollback;
the above redo record that uncommit changed must be written from redo buffer to the online redo logfile. why Oracle write the redo record that uncommit changed to the online redo logfile ? when it will be used?
We had our production database hosted on Oracle 9.2.0. Few months back we have migrated it to Oracle 10.2.0.4.0. After Migration I have noticed that redo generation has become very very high. In earlier case no. of log files generating in production hours were around 30 where as after migration it become around 200 files per day. I have run statspack report on this database. Report is saying that db block change & disk write is become very high. Parameter timed_statistics has also been set to FALSE. Even then there is not any reduction on no. of log file generation. I had used import export for upgrading the databases.
View 13 Replies View RelatedWhenever any transaction happen in database redo has generated for this transaction. Do select statement treat as a transaction as it doesn't modify any thing in database. And If select statement should not be a transaction, there should not be any redo generation for select statement.
So is select statement generate redo? If yes then Why ?
understanding a redo/undo concept . Refer following data
create table t(n number);
insert into t values(10);
commit;
now I update as following
update t set n=20;
As per my understanding the before image i.e. n=10 is stored in undo (to be used for rollback, transaction recovery and even in instance recover but not in media recovery) and after image n=20 is stored in redo (to be used for various recovery purposes including media recovery in case of consistent backup).
So it is redo logs for rolling forward and undo for rolling back making transaction, db consistent . If my above understanding is true then what is meant by the term 'redo required for undo'?
Also, if there are 2 database db1 and db2 connected using database link where we are populating t1 table in db1 using t2 table in db2 using db link where redo and undo will be updated db1 or db2?
When i was starting my database .there was an error
ora-00333:redo log read error block 203 count 8192.
We have one primary oracle database 10.2 and standby by database with no data guard. Initially we have 2 redo log group in primary and standby database.
We have recently add 2 more redo log and increase the size of log member from 50m to 200m in primary database. We don't have any problem in primary database.but in standby database we face a problem because we cannot open it. It always in mount stage in which . How we change the size of current redo log because we can't run. Alter system switch logfile command in mount stage.
Does cache buffer chain latch and buffer busy wait event are related to one any another.
Latch definition from Google says : Latches are simple, low-level serialization mechanisms to protect shared data structures in the system global area (SGA).
what does it mean my protect. Does this mean protects from aging as per LRU algorithm and getting removed from SGA
or
protect from other processes ,say from example from simultaneously DML operations.
or
both
Does buffer busy wait event occurs , because of the cache buffer chain latch ?
We are having daily syncing script which use to drop and import of one major schema.
When we do import with parameter BUFFER=209715200, it takes approximatively 4 hours & when we do without the parameter it takes 6 hours.
So i humbly request to above scenario of import process with buffer parameter in concern.
Also to expose, import is done in freeze hours.
I would like to know the buffer size using by our dba when he set export?
I know that it's possible to define it when we realize the export but its possible to know this value after export?
There's a sql*plus command to find this value?
N.B : we dont have documentation
Its for an urgent need.
i'm a student currently learning database administration security.
I need to create a tablespace for administration of database but i don't know what datafile settings are best suited for admin usage.
I have attached the schema that was given to me for this assignment.
I have a few questions and doubts regarding to cache buffer chains and lru chains.
1. What can possibly cause the cache buffers chain ?
2. Can it be resolved by increasing the free lists and increasing the inittrans of the block after identifying the hot buffers? (The table spaces are not a ASSM.)
3. How can we classify where the cache buffer chain is caused? Is there anything like extent level, header level? ( i don't understand this part due to the reason i see many operations against cache buffer chain event in stats pack reports).
4. Is cache buffer chain is related to the cache buffers chain event too?
5. In such case, tuning either of the contention will resolve the other if both exists?
What is By Default Buffer size in Oracle ......?
View 4 Replies View RelatedDoes the counter of event buffer gets include the logical reads ? Does the mertic buffer gets include the event of reading from undo buffer ?
View 4 Replies View Related/* Formatted on 2013/01/10 16:22 (Formatter Plus v4.8.6) */
CREATE OR REPLACE PACKAGE pk_batch_feds
AS
[Code]....
how can we check the size of data buffer cache.
View 7 Replies View Relatedwhat will be best buffer cache hit ratio for a database for good performance
note : in general
I want to know what exact process happens in oracle architecture when an update query is fired.
View 1 Replies View RelatedI'm trying to create a table with a select statement. I want to populate this new table with the aggregated value from a VIEW. Following is the code used for creating the VIEW,
create or replace view FINAL_WEB_LOG
as
select SESSION_ID,
SESSION_DT,
C_IP,
CS_USER_AGENT,
tab_to_string(CAST(COLLECT(web_link) AS t_varchar2_tab)) WEBLINKS
from web_views_tab
group by C_IP, CS_USER_AGENT, SESSION_DT;
I want to create a table with WEBLINKS and SESSION_ID which is a sequence from another table.
CREATE TABLE FINAL_WEB
AS
SELECT weblinks
FROM final_web_log
UNION
SELECT session_id
FROM WEB_VIEWS_TAB;
This now gives me the following error,
SQL Error: ORA-06502: PL/SQL: numeric or value error: character string buffer too small
This has to do with the field, Weblinks, it does have longer values.