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
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Buffer 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.
Script 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 RelatedDifference 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 ?
Metric Row Cache Hit Ratio In V$SYSMETRIC_HISTORY?
Mar 16, 2013understand the metric Row Cache Hit Ratio in V$SYSMETRIC_HISTORY? Is it the dictionary cache hit ratio?
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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?
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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?
Server Administration :: Negative Values Of Library Cache Hit Ratio In AWR Report
Jul 29, 2012We are getting Negative values of Library cache hit ratio in AWR Report of 11g(11.2.0.3) with Solaris[tm] OE (64-bit). Why it shows negative value.
Instance Efficiency Percentages (Target 100%)
Buffer Nowait %: 99.87 Redo NoWait %: 99.99
Buffer Hit %: 92.17 In-memory Sort %: 100.00
Library Hit %: -3,321.23 Soft Parse %: 81.95
Execute to Parse %: 92.88 Latch Hit %: 95.11
Parse CPU to Parse Elapsd %: 87.25 % Non-Parse CPU: 81.39
Data Buffer Cache
Feb 22, 2013how can we check the size of data buffer cache.
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Apr 18, 2012I want to know what exact process happens in oracle architecture when an update query is fired.
View 1 Replies View RelatedPerformance 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
Performance 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 RelatedTimesTen 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].......
Database Block And Cache Size
Oct 5, 2010In Oracle 9i
I know that db_block_size defines the standard/default block size for my datafiles.
I know db_cache_size defines the size of the my default database buffer of the size of my standard/default block size.
db_block_size = 8192 (8k)
db_cache_size = 200Mo of 8k block
Is there any needs for the other buffer cache
db_16k_cache_size
db_4k_cache_size
db_32k_cache_size
and so on?
If I have NO datafiles other than of the default block size, would I need to define a size for those other buffer pool? Is there any process that would benifit of these pools?
SQL & PL/SQL :: For Ratio Calculation?
Sep 14, 2011,i had given the sample data below
create table ex (sno number,ename varchar2(10),job_code char(4),sal number);
insert into ex values(101,'John','Java',21000,'IT');
insert into ex values(102,'Michel','BI',25000,'IT');
insert into ex values(103,'Johny','Java',30000,'IT');
[code]...
My expected output is attached in a text file
Ratio Between Global Memory Bound And Aggregate PGA Auto Target?
Aug 5, 2013SQL> select name,decode(unit,'bytes',value/1024/1024,value) as mb from v$pgastat; NAME MB---------------------------------------------------------------- ----------aggregate PGA target parameter 25600aggregate PGA auto target 2724.14648global memory bound 1024total PGA inuse 22601.7333total PGA allocated 26653.6230maximum PGA allocated
[code]....
I understand I have soft limit( aggregate PGA target parameter) which was overlimited (maximum PGA allocated = 35374.4638) hence we have over allocation count>0.Extra bytes read/written=13GB,hence we have excessive 13Gb that we had to flush on disk(excessive I/O operations) cause of limitation in 1024MB(global memory bound)(it's not enough to join or to sort something so we must do onepassor multipass) ,which defines the size of single operation of sort or join(so does it mean that it's some kind of sort_area_size and hash_area_size for automatic workarea_size_policy? and in this case what about _smm_max_size?)aggregate PGA auto target - is the amount of space(total) that Oracle can give for work areas running in automatic mode.
So I can't understand ratio between global memory bound and aggregate PGA auto target - why does the aggregate PGA auto target such tiny?(relatively process count)?Is the global memory bound static for particular aggregate PGA target parameter?
I can change it only by redefining aggregate PGA target parameter?What would be with aggregate PGA auto target if I started 10 sort operation and each of them takes about 1Gb of memory.How huge it would be? 10Gb?
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
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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?
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Oct 11, 2011What is cache/no cache & cycle/no cycle in Sequence?what is the use?
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