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Tips April 26th, 2002
Get rid of your performance problems and memory leaks!
Get rid of your performance problems and memory leaks!
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Combining apps in one JVM (Page last updated April 2002, Added 2002-04-26, Author Kirk Pepperdine). Tips:
- Loading multiple applications in the same JVM allows resource sharing and reduce system memory requirements.
- Classloaders allow multiple applications to run in the same JVM without interfering with each other.
- [Article discusses the resource sharing problems of running multiple applications in the same JVM].
J2EE worst practices (Page last updated April 2002, Added 2002-04-26, Author Brett McLaughlin). Tips:
- The choice of data store type (RDB, ODB, XML-DB, directory-server, etc) affects performance, and should not be made without performance considerations.
- Directory servers are optimized for frequent reads, with few writes. If you frequently add data to a directory server, performance degrades.
- Stateless session beans are soooo much faster.
Mobile & wireless devices (Page last updated April 2002, Added 2002-04-26, Author James White). Tips:
- Prototype to determine the performance of your device. Wireless transmissions require testing to determine if the transfer rates and processing times are acceptable.
- Attempt to create applications that can accomplish 80% or more of their operations through the touch of a single key/button or the "tap" or touch of the stylus to the screen.
- Trying to manipulate a very small scroll bar on a small screen can be an exercise in hand-eye coordination. Horizontal scrolling should be avoided at all costs. Use "jump-to" buttons rather than scrollbars.
- Try to avoid having the user remember any data, or worse, having to compare data across screens.
- Performance will always be a concern in J2ME.
- Avoid garbage generation: Use StringBuffer for mutable strings; Pool reusable instances of objects like DateFormat; Use System.gc() to jump-start or push the garbage collection process.
- Compile the code with debugging information turned off using the -g:none switch. This increases performance and reduces its footprint.
- Avoid deep hierarchies in your class structure.
- Consider third-party JVMs, many are faster than the Sun ones.
- Small XML parsers and micro databases are available for purchase where necessary.
Database comparison (Page last updated February 2002, Added 2002-04-26, Author Timothy Dyck). Tips:
- SQLServer has driver problems that slow access to it.
- Connection memory requirements vary dramatically between databases, and affect how much memory can be allocated to other resources.
- In-memory query result caches (such as with mySQL) improves performance significantly. (Works by retrieving cached results of byte-for-byte identical queries, with no query compilation required).
- Add extra indexes.
- Arrange the stored order of rows to best satisfy the queries.
- Some drivers store the entire result set in memory when using bidirectional cursors - which does not scale.
Why CMP is better than BMP (Page last updated April 2002, Added 2002-04-26, Author Tyler Jewell). Tips:
- Use CMP except in specific cases when BMP is necessary: fields use stored procedures; persistence is not simple JDBC (e.g. JDO); One bean maps to multiple tables; non-standard SQL is used.
- CMP can make many optimizations: optimal locking; optimistic transactions; efficient lazy loading; efficiently combining multiple queries to the same table (i.e. multiple beans of the same type can be handled together); optimized multi-row deletion to handle deletion of beans and their dependents.
JDBC optimizing for DB2 (Page last updated April 2002, Added 2002-04-26, Author John Goodson). Tips:
- Use the same connection to execute multiple statements.
- Keep connection objects open, and reuse them, rather than repeatedly connecting and disconnecting.
- Turn off autocommit, but don't leave transactions open for too long.
- Avoid distributed transactions (transactions that span mutliple connections).
- Minimize the data retrieved from the database, both columns and rows. Use setMaxRows, setMaxFieldSize, and SetFetchSize.
- Use the most efficiently handled data type: character strings are faster than integers, which are in turn more efficient than floating-point and timestamps.
- Use programmatic updates: updateXXX() calls on updatable resultsets. The resultset is already postioned at a row, so eliminating the usual overhead of finding the row to be updated when using an UPDATE statement.
- Cache any required metadata and use metadata methods as rarely as possible as they are quite slow.
- Avoid using null parameters in metadata queries.
- Use a dummy query to get the metadata for a column, rather than use the getcolumns()
- Use parameter markers with stored procedures, rather than embedding data literally in the statement, to minimize parsing overheads.
- Use prepared statements for repeatedly executing SQL statements
- Choose the optimal cursor: forward-only for sequential reads; insensitive for two-way scrolling. Avoid insenstive cursors for queries that only returns one row.
Finalizers (Page last updated March 2002, Added 2002-04-26, Author Phil Vickers). Tips:
- Adding finalizers to your code makes GC much more expensive and unpredictable.
- Finalizers are not executed at a predictable time.
Monitoring Networked Applications (Page last updated March 2002, Added 2002-04-26, Author Russ Currie). Tips:
- Use network probes to break down how the network is being used by the various networked applications on it.
Accelerating GUI apps (after 1.4) (Page last updated March 2002, Added 2002-04-26, Author Dana Nourie). Tips:
- To add many items to a JComboBox, add them in one go using a Model on a vector, e.g. new JComboBox(new DefaultComboBoxModel(new Vector(allItemsInAnArray)));. This generates only one changed event.
- Perform GUI operations in bulk to minimize the events generated.
- When initializing or totally replacing the contents of a model, construct a new one instead of reusing the existing one to minimize generated events.
- Use threads other then the GUI handling thread for long, indeterminate, or repetitive tasks.
- VolatileImage allows you to create a hardware-accelerated offscreen image and manage the contents of that image.
- From 1.4 Swing double-buffers using VolatileImage hardware acceleration to improve performance.
- Repaint small regions instead of entire sections or screens. For instance, when using tables, repaint a single table cell as needed instead of repainting the entire screen or table.
- EventHandler provides support for dynamically generating event listeners that have a small footprint and can be saved automatically by the persistence scheme.
MIDP tips (Page last updated March 2002, Added 2002-04-26, Author Eric Giguere). Tips:
- Make HTTP requests in a background thread.
- Use an asynchronous messaging model.
- Use WBXML to compress XML messages.
Some (Intel chip) optimization myths debunked. (Page last updated March 2002, Added 2002-04-26, Author George Walsh). Tips:
- If optimization and performance tools are used throughout development rather than tacked on at the end as a final "optimization phase," time to market and costs can actually be decreased by speeding up the process of locating problems and bottlenecks in code.
- Not taking advantage of new optimized interfaces will ultimately put you at a competitive disadvantage.
EJB Clustering (Page last updated February 2002, Added 2002-04-26, Author Tyler Jewell). Tips:
- Four locations that can provide clustering logic for an EJB are: the JNDI naming server where the home stub is bound, the container, the home stub, and the remote stub.
Assertions (Page last updated April 2002, Added 2002-04-26, Author Glen McCluskey). Tips:
- Disabled assertions add a cost of one check of a global state flag
- Enabled assertions add a cost of a check of a global state flag and evaluating the boolean expression. Also the cost of throwing a new exception is added if the assertion fails.
- Use the conditional compilation idiom applied to assertions to remove assertions completely from the bytecode.
Java transaction management (JTS) (Page last updated April 2002, Added 2002-04-26, Author Brian Goetz). Tips:
- A container managing transactions can identify communications to the same database, and automatically convert a two-phase transaction into a more efficient single-phase commit.
JDBC Drivers (Page last updated March 2002, Added 2002-04-26, Author Barrie Sosinsky). Tips:
- Type 1 drivers are JDBC-ODBC bridges, plus an ODBC driver. Recommended only for prototyping, not for production. Not suitable for high-transaction environments. Not well supported, and limited in functionality.
- Type 2 drivers use a native API, and are part-Java drivers. Have a binary-code client loading overhead, and may not be fully-featured.
- Type 3 drivers are a pure Java driver which connects to database middleware. Can be server-based which is frequently faster than types 1 and 2.
- Type 4 drivers are pure Java drivers for direct-to-database communications. This can minimize overheads, and generally provides the fastest driver.
- JDBC 3.0 has additional features to improve performance such as advancements in connection pooling, statement pooling, RowSet objects.
- Opening a connection is the most resource-expensive step in database transactions. Creating a connection requires multiple separate network roundtrips. However, once the connection object has been created, there is little penalty in leaving the connection object in place and reusing it for future connections.
- Connection pooling, keeps open a cache of database connection objects, making them available for immediate use. Instead of performing expensive network roundtrips to the database server to open a connection, a connection attempt results in the re-assignment of a connection from the local cache.
- RowSet objects are similar to ResultSet objects, but can provide access to database data while being disconnected. This allows data to be efficiently cached in its simplest form.
- Prepared statement pooling (available from JDBC 3.0) caches SQL queries that have been previously optimized and run so that, should they be needed again, they do not have to go through optimization pre-processing again (avoiding optimization steps, such as checking syntax, validating addresses, and optimizing access paths and execution plans). Statement pooling can be a significant performance booster.
- Statement pooling and connection pooling in JDBC 3.0 can cooperate to share statement pools, so that connections that can use a cached statement from another connection, thus incurring statement preparation overheads only once on the first execution of some SQL by any connection.
- Database drivers developed by vendors other than the the database vendor can be better performing and more feature full. (Driver vendors concentrate on the driver, database vendors have many other things to consider).
- Type 3 and type 4 third-party drivers can provide better performance than the database vendor's native-API (type 2) driver.
- Try to use a driver that supports JDBC 3.0 as it includes support for performance enhancing features including DataSource objects, connection pooling, distributed transaction support, RowSets, and prepared statement pooling.
- Type 3 and Type 4 drivers are the drivers to use when performance is important.
Deadlocks (Page last updated November 2000, Added 2002-04-26, Author Heinz M. Kabutz). Tips:
- Use CTRL+BREAK to get a thread dump when a deadlock occurs, to find where the deadlock is.
- Use SwingUtlities.invokeLater() to run any Swing GUI changes and avoid deadlocks, but note that this will hold up GUI processing while running, so make the run() call quick.
- Use SwingUtilities.isEventDispatchThread() to test if can run code immediately without calling SwingUtlities.invokeLater().
Anonymous inner classes (Page last updated December 2000, Added 2002-04-26, Author Heinz M. Kabutz). Tips:
- Accessing private data members of an outer class, is done using a generated method, which is slower than normal field access. Though HotSpot can inline the access.
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