Difference Between Cache Buffer Chain Latch And Buffer Busy Wait
Jul 30, 2012
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 ?
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Apr 25, 2013
I want to simulate latch : cache buffer chains wait event due to use of nested loop join for lookup tables
This is what a tried :
-- create parent / child tables
SQL>drop table emp1 purge;
drop table dept1 purge;
create table dept1 (dept_id number primary key,
dept_name char(30));
[Code]....
I traced many queries like the one given below (dept_id between 1 and n where n varied from 10 to 1000) but they always result in hash join
1* select d.dept_name, e.id from sys.dept1 d, sys.emp1 e where d.dept_id = e.dept_id and e.dept_id < 1000
Execution Plan
----------------------------------------------------------
Plan hash value: 619452140
----------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 998K| 41M| 680 (2)| 00:00:09 |
|* 1 | HASH JOIN | | 998K| 41M| 680 (2)| 00:00:09 |
|* 2 | TABLE ACCESS FULL| DEPT1 | 999 | 34965 | 4 (0)| 00:00:01 |
|* 3 | TABLE ACCESS FULL| EMP1 | 999K| 8780K| 672 (2)| 00:00:09 |
----------------------------------------------------------------------------
what can I do to get a nested loop join to simulate latch : cache buffer chains?
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Dec 20, 2011
I noticed oracle background process ora_fbda_padwsdpr is suffering from buffer busy wait. When i further finding the object, it was on SYS_FBA_FA tables.
what is this is causing BUFFER BUSY WAIT. Also to add we have disabled flashback database.
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Oct 2, 2013
I've have a system where the most buffer waits are spent on system tables like
SYS.DBMS_ALERT_INFO
and SYS.DBMS_LOCK_ALLOCATED
Would it convert the system tablespace from dictionary managed to locally managed?
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Oct 3, 2010
Is there any relationship b/w tuning BUFFER CACHE and BUFFER BUSY WAITS?
1) Buffer Busy Waits are happening as the User process found the same Datablock is being used by another user in the BUFFER CACHE.
2) And also happens, when the server process found the same Datablock are being used in the Datafile.
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Oct 25, 2010
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?
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Feb 22, 2013
how can we check the size of data buffer cache.
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May 20, 2013
what will be best buffer cache hit ratio for a database for good performance
note : in general
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Apr 18, 2012
I want to know what exact process happens in oracle architecture when an update query is fired.
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Mar 26, 2012
give a script to find how much my db buffe cache and redo log buffer cache is used and how much is free.
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Mar 3, 2011
Database : 9.2.0.7
Os : windows 2003 sevrer standdard edition
RAM 4 Gigs
The buffer cache hit ratio in this server is around 83%, where it normaly was around 98% before i did some maintenance activities.
I have done some maintenance activities in January on this database.
Maintenance activties includes below steps
1.In production i have deleted old data in the production tables
2.Reorganized tablespaces,tables
3.Rebuild indexes for those tables.
4. At last collected statistics for those tables.
Now after this activity the buffer cache hit ratio is very low.
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Nov 30, 2012
Considering the below factors, I am planning to increase the buffer cache value from 256Mb to 512Mb.
1. Buffer cache hit ratio value is around 35% even in the normal period.
2. free buffer requested value is below during peak & normal hours below.
Statistic Total per Second per Trans
--------------------------------- ------------------ -------------- ------------
free buffer requested 54,694,995 15,226.9 2,523.7
free buffer requested 23,412,674 6,501.7 2,585.9
3. most of the top 5 physical reads & logical reads queries are well tuned and some of queries are doing FTS on small tables (table count min 1500 max 35000). SO indexing option is not required for these queires. But these queries getting executed frequently.
SQL> show sga
Total System Global Area 2148534928 bytes
Fixed Size 731792 bytes
Variable Size 1879048192 bytes
Database Buffers 268435456 bytes
Redo Buffers 319488 bytes
5.top 5 waitevents during db slow performance & high cpu utilization (>80%) issue.
Top 5 Timed Events
~~~~~~~~~~~~~~~~~~ % Total
Event Waits Time (s) Ela Time
-------------------------------------------- ------------ ----------- --------
latch free 1,848,898 153,793 52.00
buffer busy waits 395,280 87,201 29.49
db file scattered read 3,488,648 34,199 11.56
enqueue 4,052 10,897 3.68
CPU time 5,567 1.88
6. Top 5 waitvents during normal activities and CPU utilization is around 40%.
Top 5 Timed Events
~~~~~~~~~~~~~~~~~~ % Total
Event Waits Time (s) Ela Time
-------------------------------------------- ------------ ----------- --------
CPU time 1,860 45.32
db file scattered read 1,133,669 985 23.99
imm op 776 605 14.73
sbtinfo2 208 139 3.40
sbtbackup 2 123 3.00
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Sep 27, 2010
1) Is shutting down the DB flush all the data buffers, from the buffer Cache?
2) In any oracle version, do we have any way to flush only the buffer Cache.
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Aug 19, 2010
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?
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Mar 28, 2011
How can i know which objects used keep buffer cache?
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Jan 15, 2011
I have some confusion about Keep Pool in Buffer Cache.
1. What is the reasoning for placing a table in the KEEP buffer pool because if it is frequently accessed, it will be around when needed (ie if it is constantly being accessed it will not age out) .
2. Would the table be still in the Default Pool if the Keep Pool is not sized and the command is being issued alter TABLE SCOTT.EMP storage (buffer_pool keep) ?
3. If the database is restarted will the table be wiped out of the Keep Pool and again be pinned to the Keep Pool ?
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Jun 14, 2013
If sga Buffer Cache Size consume full of SGA_target size, if possible that it will cause performance any issue. I am facing CPU 100% consuming while single query execute, Which query generate monthly report data.
I have two question
1)How to fix the CPU 100% consuming
2)How to find total number user hit oracle specific schema.
Oracle 10.2.0.5 Standard
Sga_target : 14G
Sga_max :20G
Pga :3G
Below SGA details
NAME BYTES/1024/1024
-------------------------------- ---------------
Fixed SGA Size 2.01795197
Redo Buffers 13.9804688
Buffer Cache Size 13632
Shared Pool Size 640
Large Pool Size 16
Java Pool Size 16
Streams Pool Size 16
Granule Size 16
Maximum SGA Size 20480
Startup overhead in Shared Pool 208
Free SGA Memory Available 6144
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Jan 26, 2011
Say 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?
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May 7, 2011
I am currently in the favorable situation in which I have excess amounts of memory available on the database server - a single node setup. The server only serves the single instance and no other processing. Database size is around 2.3tb and memory is 50gb. For the majority of processing, AIX is allocating a significant amount (anywhere from 30-40%) of the memory to the AIX file system cache (persistent pages).
I've been trying to find documentation about this, but have not had any luck yet. My guess is that it would be better to allow Oracle to cache this data - meaning increase the SGA target and max size to allow for a larger buffer cache. However, the nice thing about the AIX cache is if process memory is needed, the file system cache gives up pages. If the memory was allocated to the SGA, its pretty much locked in.
I have read several articles stating that a larger buffer cache is not always better, as a larger cache takes more management. But having both of the caches active seem to be a waste of memory, effectively storing the data twice - once in AIX persistent pages and a second time in Oracle database buffer cache.
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May 30, 2013
I have a serious doubt in oracle architecture functionality, when a user issues a update statement the data blocks are carried to db buffer cache and where does the changes to the data blocks are made???? Does a copy of the data block is kept in db buffer cache and the changes are made to the block in buffer cache?? or the a copy of the data block is kept in undo tablespace and changes are made to the blocks in the undo tablespace???
In simple the changes to the data blocks are made at db buffer cache or undo tablespace?
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Feb 24, 2013
Oracle Version: 11.1.0.7.0
Active Dataguard
Statspack has been configured for Active Dataguard on Primary database.We got an spike of Buffer busy waits for about 5 min in Active Dataguard, this was causing worse Application SQL's response time during this 5 min window.Below is what i got from statspack report for one hour
Snapshot Snap Id Snap Time Sessions Curs/Sess Comment
~~~~~~~~ ---------- ------------------ -------- --------- -------------------
Begin Snap: 18611 21-Feb-13 22:00:02 236 2.2
End Snap: 18613 21-Feb-13 23:00:02 237 2.1
Elapsed: 60.00 (mins)
[code]...
Why there could sudden spike of demand on UNDO data in Active Data Guard ?
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Jun 20, 2013
What is the difference between cache fusion and Cache Coherency. Both are same or different functionality.
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Apr 12, 2013
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.
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Apr 30, 2013
What is By Default Buffer size in Oracle ......?
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Jun 27, 2012
Does the counter of event buffer gets include the logical reads ? Does the mertic buffer gets include the event of reading from undo buffer ?
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Jan 10, 2013
/* Formatted on 2013/01/10 16:22 (Formatter Plus v4.8.6) */
CREATE OR REPLACE PACKAGE pk_batch_feds
AS
[Code]....
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Dec 14, 2012
I'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.
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Oct 7, 2010
I am running script which drop all public synonyms and create private synonyms for all eligible objects. I am passing value to procedure through cursor and I am using dbms_output.
ERROR at line 1:
ORA-20000: ORU-10027: buffer overflow, limit of 999999 bytes
ORA-06512: at "SYS.DBMS_OUTPUT", line 32
ORA-06512: at "SYS.DBMS_OUTPUT", line 97
ORA-06512: at "SYS.DBMS_OUTPUT", line 112
ORA-06512: at line 101
I read that by: SET SERVEROUTPUT ON SIZE unlimited would resolve this problem.
What are the effects?Do I need to check any disk space, or any effect on the memory?
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Aug 25, 2013
is there any method to store a value in "copy buffer" ?
I mean, for example, if i have defined a global varaiable as
Quote::global.name := 'orafaq';
Then what i need is a command something like:
windows_copy_buffer := :global.name ;
So that later on when i press control+v, then it paste the word "orafaq".
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Mar 3, 2010
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?
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