Java Application Tuning

Tuning objectives

Tools used
Jprofiler
JRockit mission control
Wily introscope
Fluke
Splunk
Wireshark

testing - load runner, winruuner, junit, jmeter

Measurement
CPU (ideally should not cross more than 50-75%)
Memory
IO usage
Response time
Latency
Throughput

Application level tuning

Java language tuning
Using hashmaps vs hashtable, array vs vector,
Use StringBuffer to Concatenate Strings
Assign null to Variables That Are No Longer Needed
Declare Constants as static final
Avoid Finalizers - Adding finalizers to code makes the garbage collector more expensive and unpredictable
Synchronize Only When Necessary

EJB

JNDI

Application Server
Precompile jsps

OS
File Descriptors
set rlim_fd_max = 8192
Verify this hard limit by using the following command:
ulimit -a -H
Once the above hard limit is set, increase the value of this property explicitly (up to this limit)using the following command:
ulimit -n 8192
Verify this limit by using the following command:
ulimit –a

DISK IO settings

TCP/IP settings

Virtual memory settings

Run TOP command in Linux to check CPU usage.
Run VMSTAT, SAR, PRSTAT command to get more information on CPU, memory usage and possible blocking.
Enable the trace file before running your queries,then check the trace file using tkprof create output file.
According to explain plan check the elapsed time for each query,then tune them respectively.

What is the use of iostat/vmstat/netstat command in Linux?
Iostat – reports on terminal, disk and tape I/O activity.
Vmstat – reports on virtual memory statistics for processes, disk, tape and CPU activity.
Netstat – reports on the contents of network data structures.

Caching

JVM tuning/Garbage collection
best GC algorithm, especially for web server applications, is the Concurrent Mark Sweep GC
operation mode to server

-Xms, -Xmx
-XX:PermSize=256 m -XX:MaxPermSize=256m --> this option is not there in new HotSpot JVM
Log GC -Xloggc:$CATALINA_BASE/logs/gc.log -XX:+PrintGCDetails
-XX:+PrintGCDateStamps
HeapDump on Out of memory - -Xloggc:$CATALINA_BASE/logs/gc.log -XX:+PrintGCDetails -XX:+PrintGCDateStamps

jvm - space ratios,
gc type – CMS (concurrent mark and sweep, parallel), G1 (this is new in HotSpot)

In the event CPU usage rate is high - If TPS is low but CPU usage rate is high, this is likely to result from inefficient implementation. In this case, you should find out the location of bottlenecks by using a profiler. You can analyze this by using jvisuavm, TPTP of Eclipse or JProbe.
     
JMS tuning
quota - space for jms messages at queue or jms server level. if quota limit is reached, exception is raised
send timeout - blocking producers when quota limits are reached
paging messages
message buffer size - amount of memory stored in memory before messages are paged out
message compression
expired messages

JDBC code tuning
Use prepared statements. Use parametrized SQL.
Tune the SQL to minimize the data returned (e.g. not 'SELECT *').
Minimize transaction conflicts (e.g. locked rows).
Use connection pooling.
Try to combine queries and batch updates.
Use stored procedures.
Cache data to avoid repeated queries.
Close resources (Connections, Statements, ResultSets) when finished with.
Select the fastest JDBC driver.

JDBC parameter tuning
Increasing Performance with the Statement Cache
Connection Testing Options for a Data Source - test frequency/
Minimized Connection Test Delay After Database Connectivity Loss
Minimized Connection Request Delay After Connection Test Failures
Minimized Connection Request Delays After Loss of DBMS Connectivity
Minimizing Connection Request Delay with Seconds to Trust an Idle Pool Connection
A leaked connection is a connection that was not properly returned to the connection pool in the data source. To automatically recover leaked connections, you can specify a value for Inactive Connection Timeout on the JDBC Data Source

Threadpool/work manager
Contention/locks
Minimize I/O
Parellelization/concurrency

Hibernate tuning

property name="show_sql"

Tip 1 - Reduce primary key generation overhead
Tip 2 - Use JDBC batch inserts/updates
Tip 3 - Periodically flush and clear the Hibernate session
entityManager.flush();
entityManager.clear();

Tip 4 - Reduce Hibernate dirty-checking overhead
@Transactional(readOnly=true)
public void someBusinessMethod() {
}

Tip 5 - Search for 'bad' query plans - full table scans and full cartesian joins
Tip 6 - Use the second-level and query caches
Define lazy loading as the preferred association loading strategy,
Set ReadOnly to "true" on Queries and Criteria, when objects returned will never be modified.

Cache – 1st level = Session, 2nd = Hibernate, 3rd = Query results cache

SQL Tuning
How to see execution plan for an SQL
SQL> set autotrace onSQL> select count(*) from table_name;
SQL> explain plan set statement_id = '111' for select * from tableName;SQL> select * from plan_table;

How to find out cpu time for an SQL?
SQL> TIMING START select_empSQL> SELECT * FROM employee ; SQL> TIMING SHOW select_emp timing for: select_emp real: 1760
use indexes, improve h/w, caching, tune it, hints,
use explain plan or sql analyzer to see the execution path
add hints
rewrite sql
replace sql with pl/sql

How would you improve a poor performing query?

How do you tune a sql statement?

understand row level lock and how it migrates to table level lock

soa performance tuning - dehydrate, db persistence
http://docs.oracle.com/cd/E25178_01/core.1111/e10108/bpel.htm

Oracle HTTP server tuning
http://docs.oracle.com/cd/E25178_01/core.1111/e10108/http.htm#ASPER99006