1. Office of the Accountant General (A&E) Andhra Pradesh Hyderabad
TUNING
Office of the Accountant General (A&E)
Andhra Pradesh
Hyderabad

2. Tuning When is tuning necessary? What is to be tuned?
Only if you feel that application is not running fast enough
What is to be tuned?
Oracle database
Application
Operating system
Network

3. Tuning Goals To optimize the performance of database
To make database available to users without making them wait for resources
To perform maintenance operations without interrupting users

4. Tuning Parameters Response time Database availability
Database hit percentages
Memory utilization

5. Tuning Steps Tune the design Tune the application Tune memory Tune IO
Tune contention
Tune operating system

6. Tuning Considerations
Different for
OLTP databases
DSS databases
Hybrid databases
Our database
Hybrid database
Data entry and Report generation done simultaneously

7. Hybrid Databases Number of rollback segments for data entry
Some large rollback segments for report generation
Balanced db_block_buffers and log_buffers
Medium size for db_block_size

8. Tuning Hybrid Databases
Tuning application is important in hybrid databases
Indexing plays an important role
Schedule batch processing if it is heavy on resources
Use less number of bind variables in reports
Optimize queries using hints

9. Views, Utilities and Tools Used For Tuning
Dynamic troubleshooting/performance and dictionary views
V$XXXX dynamic troubleshooting and performance views
DBA_XXX dictionary views
Utlbstat.sql and utlestat.sql
Alert logs and traces
nitialization parameters I

10. Tuning Statistics To Be Gathered
Library cache statistics
System statistics
Wait event statistics
Latch statistics
Rollback contention statistics
Buffer busy wait statistics
Dictionary cache statistics
IO statistics per data file/table space
Period of measurement

11. Alert Log Files
The lert log file consists of a chronological log of messages and errors
Check the alert log file to:
Detect internal errors and block corruption errors
Monitor database operations
View the non-default initialization parameters
Remove or trim the alert log file regularly after checking a

12. Background Processes Trace Files
The Oracle server dumps information about errors detected by any background process in trace files
Oracle support uses these trace files to diagnose and trouble shoot problems

13. User Trace Files
Server process tracing is enabled or disabled at the session or instance level by:
The ALTER_SESSION command
The SET_SQL_TRACE_IN_SESSION procedure
The initialization parameter SQL_TRACE
A user trace file contain statistics for traced SQL statements for that session
A user trace file is used for SQL tuning
The Oracle database creates user trace files on per server process basis

14. Tuning Memory The amount of memory occupied by Oracle is called SGA
SGA contains
DB Block Buffers
Redo Log Buffers
Shared Pool
Library Cache
Data Dictionary Cache
UGA
Large Pool

15. Tuning Memory
In hybrid databases like VLC, memory plays an important role
Ideally DB_BLOCK_BUFFERS and LOG_BUFFERS to be in ratio
SHARED_POOL_SIZE also plays an important parameter in tuning memory

16. Tuning Library Cache Library Cache tuned V$Views
If the pins to misses ratio is more than 1%
If the get hit ratio of name space is less than 90%
V$Views
V$LIBRARYCACHE
V$SQLAREA
V$SQLTEXT
V$DB_OBJECT_CACHE

17. Tuning Library Cache To find hit ratio of library cache
Select namespace, gethitratio from v$librarycache
To find reloads of SQL statements
Select sql_text, users_executing, executions, loads from v$sqlarea
To find library cache reloads
Select sum(pins) Executions, sum(reloads) Misses, sum(reloads)/sum(pins) Hitratio from v$librarycache

18. Tuning Library Cache Keep often used objects Avoid parsing
Avoid large anonymous PL/SQL Blocks
Select sql_text from v$sqlarea where command type=47;
Reserve un-fragmentable memory in shared pool
SHARED_POOL_RESERVED_SIZE
SHARED_POOL_MIN_ALLOC

19. Tuning Data Dictionary Cache
Keep the ratio of the getmisses to gets less than 15%
Select parameter, gets, getmisses from v$rowcache
Increase shared pool size if the above ratio is more than 15%

20. Tuning DB Block Buffer Cache
DB hit ratio should always be more than 90%
To find DB Cache hit ratio
Select 1-(p.value)/(d.value+c.value) from v$sysstat p, v$sysstat d, v$sysstat c where p.name = ‘physical reads and d.name = ‘db block gets’ and c.name = ‘consistent gets’;

21. Tuning Buffer Cache If DB hit ratio gets below 90%
Increase buffer cache size
Use multiple buffer pools
Cache tables
Bypass the buffer cache for sorting and parallel reads

22. Tuning Buffer Pool To use multiple pool buffers set
DB_BLOCK_BUFFERS
DB_BLOCK_LRU_LATCHES
BUFFER_POOL_KEEP
BUFFER_POOL_RECYCLE
To enable table caching
Alter table with cache clause
Use cache hint in query

23. Tuning Redo Log Buffer Following parameters effect log buffer
LOG_CHECK_POINT_INTERVAL
LOG_CHECK_POINT_TIMEOUT
Check for
Redo buffer space event
Redo buffer allocation retries
Redo log space requests
Logfile switch (check point incomplete)
Logfile switch (archive needed)

24. Tuning Check Point Each checkpoint cause IO operations
Frequent checkpoints reduces runtime performance
Parameters
FAST_START_IO_TARGET
LOG_CHECK_POINT_INTERVAL
LOG_CHECK_POINT_TIMEOUT
DB_BLOCK_MAX_DIRTY_TARGET
LOG_CHECK_POINT_TO_ALERT

25. Tuning Large Pool Used for oracle maintenance operations
UGA in MTS mode
Parallel query
IO-server process
Tuning parameters
LARGE_POOL_SIZE
DBWR_IO_SLAVES

26. Latches Contention areas that the DBA can tune: Latch types
Redo allocation latch
Redo copy latch
LRU latch
Latch types
Willing to wait
Gets, misses, sleeps
Immediate
Immediate gets and immediate waits

27. LRU Latches
LRU latches regulate the least recently used (LRU) lists used by the buffer cache
By default, the Oracle server set the number of LRU latches to one-half the number of CPUs, with a minimum of one
Each latch controls a minimum of 50 buffers

28. LRU Latch Tuning Goals
Ensure there are sufficient number of LRU latches for the data buffer cache so that contention between server processes is minimized
Balance the number of latches with the number of CPUs
Set one DBWn process for each latch

29. Resolving LRU Latch Contention
If the hit percentage for the LRU latch is less than 99%
Increase the number of LRU latches by setting the parameter DB_BLOCK_LRU_LATCHES
The maximum number of latches is the lower of:
Number of CPUs*2*3
Number of buffers/50

30. Free Lists
A free list for an object maintains a list of blocks that are available for inserts
The number of free lists for an object cannot be set dynamically
Single CPU systems do not benefit greatly from multiple free lists
The tuning goal is to ensure that an object has sufficient free lists to minimize contention

31. Resolving Free List Contention
Query the V$SESSION_WAIT view
Identify the object and get free lists for the segment from DBA_SEGMENTS
Re-create the object in question

32. Tuning IO-contentions
Keep data files and log files on separate disks
Stripe table data
Reduce Disk IO
Evaluate the use of RAW devices
To know IO of files
Select d.name, f.phyrds, f.phyrds from v$datafile d, v$filestat where d.file# = f.file#

33. Oracle File Striping Operating system striping Manual striping
Use operating system striping software or RAID
Decide on the right stripe size
Manual striping
Use the create table or alter table ALLOCATE command
Is worth while with parallel query usage

34. Tuning Data Files
Keep data files and log files on separate disks to reduce IO contention
Specify the initialization parameter DB_FILE_MULTIBLOCK_READ_COUNT
To determine the number of database blocks the server reads at once
To influence the execution plan of the cost-based optimizer

35. Tuning Log Files Size redo log files to minimize the contention
Have enough groups to prevent waiting
Store redo log files on separate faster devices
Dynamic views
V$LOG
V$LOGFILE

36. Tuning Archive Log Files
Keep archive log files on separate IO faster devices
Archive log operations parameters
LOG_ARCHIVE_MAX_PROCESSES
LOG_ARCHIVE_DEST
Dynamic views
V$ARCHIVE_DEST
V$ARCHIVE_LOG
V$ARCHIVE_PROCESSES

37. Tuning Rollback Segments
Transactions should never wait for access to rollback segments
Rollback segments should not extend during normal running
Users and utilities should try to use less rollback
No transaction should ever run out of rollback space
Readers should always see the read-consistent images they need

38. Tuning Rollback Segments
The ratio of the sum of waits to the sum of gets should be less than 1%
Select sum(gets) ‘gets’, sum(waits) ‘waits’, sum(waits)*100/sum(gets) ‘ratio’ from v$rollstat;
If the ratio is more than 1% then create more rollback segments
The number of waits for any class should be less than 1% of the total number of requests

39. Sizing Transaction Rollback Data
Deletes are expensive
Inserts use minimal rollback space
Updates use rollback space depending on the number of columns
Index maintenance adds rollback

40. Possible Problems Transactions fails for lack of rollback space
“Snapshot too old” error occurs if:
The inserted transaction list in the block being queried has been reused, and the SCN in the block is newer than the SCN at the start of the query
The transaction slot in the rollback segment header has been reused
The undo data in the rollback segment has been overlaid after a commit

41. Tablespace Usage
Reserve the SYSTEM tablespace usage for data dictionary objects
Create locally managed tablespaces to avoid space management issues
Split tables and indexes into separate tablespaces
Create separate rollback tablespaces
Store very large database objects in their own tablespace
Create one or more temporary tablespaces