Data Buffer Cache
Feb 22, 2013how can we check the size of data buffer cache.
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Difference Between Cache Buffer Chain Latch And Buffer Busy Wait
Jul 30, 2012Does 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 ?
Oracle Data Changes In Undo Tablespace / Database Buffer Cache
May 30, 2013I 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?
Buffer Cache Hit Ratio For A Database
May 20, 2013what will be best buffer cache hit ratio for a database for good performance
note : in general
Query Parsing And Buffer Cache?
Apr 18, 2012I want to know what exact process happens in oracle architecture when an update query is fired.
View 1 Replies View RelatedScript For Monitoring Database Buffer Cache
Mar 26, 2012give a script to find how much my db buffe cache and redo log buffer cache is used and how much is free.
View 1 Replies View RelatedBuffer Cache Hit Ratio Is Low In Oracle 9i After Maintenance
Mar 3, 2011Database : 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.
Performance Tuning :: Increasing Buffer Cache Value
Nov 30, 2012Considering 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
Performance Tuning :: Flushing Buffer Cache
Sep 27, 20101) 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.
Server Administration :: DELETE And Buffer Cache?
Aug 19, 20101)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 RelatedServer Administration :: How To Know Which Objects Used Keep Buffer Cache
Mar 28, 2011How can i know which objects used keep buffer cache?
View 5 Replies View RelatedPerformance Tuning :: Keep Pool In Buffer Cache
Jan 15, 2011I 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 ?
Simulate Latch : Cache Buffer Chains
Apr 25, 2013I 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?
Buffer Cache Size Consume Full SGA_target
Jun 14, 2013If 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
Server Administration :: Database Buffer Cache Configured As 2M
Jan 26, 2011Say 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 RelatedPerformance Tuning :: Oracle Buffer Versus AIX Filesystem Cache
May 7, 2011I 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.
Performance Tuning :: Relationship Between Buffer Cache And Busy Waits
Oct 3, 2010Is 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.
Real Application Clusters :: Difference Cache Fusion and Cache Coherency
Jun 20, 2013What is the difference between cache fusion and Cache Coherency. Both are same or different functionality.
View 1 Replies View RelatedData Guard :: Buffer Busy Waits On UNDO Data In Active DG
Feb 24, 2013Oracle 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 ?
TimesTen In-Memory :: AWT Cache Group With Cache Awt Parallelism
Jul 10, 2012I have some question.
TTversion : TimesTen Release 11.2.2.3.0 (64 bit Linux/x86_64) (tt112230:53376) 2012-05-24T09:20:08Z
We are testing a AWT cache group ( with CacheAwtParallelism=4 ).
Application(1 process) to the DML generates to TimesTen(DSN=TEST).
At this point, Are delivered to the 4 parallel DML?
[TEST]
Driver=/home/TimesTen/tt112230/lib/libtten.so
DataStore=/home/TimesTen/DataStore/TEST/test
PermSize=1024
TempSize=512
PLSQL=1
[code].......
Performance Tuning :: Data Dictionary Cache - Dc_objects
Jul 4, 2011In order to improve the performance of our live server, I am trying to do an exhaustive comparison with our test environment which is quite quick in spite of the fact that we port the data from Live every month.
There are no obviously slow queries appearing in the the top SQLs of AWR, we have optimised such things already. Right now it is about general uplift rather than SQL based tuning.
I picked up random SQLs and I noticed a marked differences in the execution time. Typically they are 3 to 4 times and there are cases much more than that.
1. I observed that, while the explain plan of the queries are same, trace of the queries give a different picture. I have observed that the recursive calls, consistent gets and sorts(memory) are quite high on Live.
2. I have no solid reasons to say this but my instincts tell me that the recursive calls is the major contributing factor. It is sometimes 2000+ for an SQL.
3. On googling more on that, it finally made me compare the data dictionary on the AWR report of test and Live.
The dc_objects caught my eyes. In that 4 hour AWR, there were about 10 million get requests and the pct miss was ~10. For similar load, the test server had 5 million gets with 0.08 PCT miss for 4 hours.
Index In Cache
Apr 21, 2013i have a application which uses 32 tables for retrieval in this 4 tables are important and have a size more than 100 mb can i move the index of these 4 tables cache memory to improve the applications retrieval performance if i done so ,then that will affect any other applications performance
View 1 Replies View RelatedHow To Set Sequence Cache
Oct 10, 2012Are there any recommendations or good practices to set sequence CACHE parameter (for example one caching per hour, day etc)?
View 4 Replies View RelatedBuffer Used In Export?
Apr 12, 2013I 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.
Cache Buffers Chains In RAC
Jun 1, 2012I have a query - whch used to be run in 30 minutes and now hangs on for hours and not finishing. The wait i see is
wait event latch: cache buffers chains.
This is a 11.1.0.7 2 Node RAC environment runing on HP-UX Itanium.
Procedure To Activate Cache
Aug 16, 2010i m working on oracle 10g using db_block_buffers. But i m not able to get information from database cache advice. Is there any method or procedure to activate cache advice despite of db_block_buffers use?
View 2 Replies View RelatedSQL & PL/SQL :: What Is Cycle And Cache In Sequence
Oct 11, 2011What is cache/no cache & cycle/no cycle in Sequence?what is the use?
View 3 Replies View RelatedBuffer Chain Latches
Oct 25, 2010I 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?
SQL & PL/SQL :: By Default Buffer Size?
Apr 30, 2013What is By Default Buffer size in Oracle ......?
View 4 Replies View RelatedBuffer Gets And Logical Reads?
Jun 27, 2012Does 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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