Advanced Distributed Transaction Processing with BEA WebLogic Server 6.0

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Ed Felt Sriram Srinivasan ed.felt_at_bea.com,
srirams_at_bea.com BEA Systems, Inc.
Advanced Distributed Transaction Processing with
BEA WebLogic Server 6.0
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Agenda

• Why use transactions?
• What capabilities does BEA WebLogic Server 6.0
  provide?
• How to program?
• How to configure and monitor?
• References
• Questions Answers

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Benefit 1 Data Consistency

• Ensure data integrity when accessing more than
  one data store, especially in distributed
  environment
• Simple model for application programmer
• A - atomic
• C - consistent
• I - isolated
• D - durable

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Benefit 2 Monitoring Management

• A transaction is a higher-level unit of work than
  a database query or an object invocation
• BEA WebLogic Server allows transactions to be
  given a semantic name (TransferFunds or
  ReserveSeat or CheckOut)
• Transaction Name is reported in error messages
• Statistics subtotals categorized by Transaction
  Name

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Benefit 3 Timeouts Overload Protection

• Transactions are subject to timeout
• 30 second default
• Application code (or the EJB container) can mark
  a transaction rollback only
• In an overloaded system, BEA WebLogic Server
• Times out requests (who waits 30 seconds for a
  Web page to return?)
• Avoids wasted work on doomed transactions
• Eventually refuses to begin new transactions when
  there are too many already running (configurable
  parameter)

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Supported Configurations

• Multiple servers may participate in a distributed
  transaction
• Clustered or non-clustered
• Need not be in same administrative domain
• Requires connectivity and permissions
• Clients may initiate transactions and infect
  multiple servers
• Commit responsibility is handed off to a server
• Clients may not enlist resources or register
  synchronization callbacks
• Multiple XA resources may participate in same
  transaction
• More than one coordinated by two-phase commit
  algorithm

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Relationship with Other Subsystems

• JDBC
• Recognized any JDBC driver that implements JDBC
  2.0 XA extensions
• BEA provides Type 2 XA driver for Oracle 8.1.6
  client
• JDBC wrapper enhances performance
• JMS
• Supports XA, can participate in JTA transactions
• All storage types database, file, non-persistent
• EJB
• Automatically manages transactions based on EJBs
  deployment descriptor

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High-Level Architecture
EJB Container
Application
JMS
JDBC
JTA
JTA
JDBC Wrapper
JDBC
Transaction Manager
XA-Capable Resource
XA
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Performance Optimizations

• Boxcar algorithm for multiple commit records per
  I/O
• One-phase commit optimization
• Read-only branch optimization
• Dynamic resource enlistment optimization
• Piggy-back transaction propagation
• Multiple operations per coordination message
• Asynchronous, parallel coordination architecture
  with retry

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Programming APIs

• Good news! In many cases, transactions are
  controlled by the EJB Container, and an
  application programmer writes no code for
  transactions
• The UserTransaction object provides simple
  begin/commit/rollback functionality for
  applications that need to explicitly demarcate
  transaction boundaries
• More powerful transaction objects normally used
  by the Application Server and EJB Container are
  available to applications with complex
  transactional requirements
• BEA WebLogic Server extensions for convenience
  and added value

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JTA Interfaces

• UserTransaction
• Basic methods to begin, commit, rollback
  transactions and get/set status
• TransactionManager
• Adds suspend, resume, get threads current
  Transaction object
• Transaction
• Represents on transaction, controls enlistment
  and synchronization
• Synchronization
• Callback interface for before/after completion
  notification
• XAResource
• Xid
• Various exceptions and status codes

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BEA WebLogic Server Extensions

• weblogic.transaction.TxHelper
• Static methods to get Transaction,
  UserTransaction, and TransactionManager objects
• weblogic.transaction.Transaction
• Get/set transaction name, transaction properties
• Get/set rollback reason
• Get timeout information
• Get Xid
• weblogic.transaction.TransactionManager
• XA resource registration
• Get transaction object by Xid
• Force suspend/resume (without XA calls)

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Configuration Parameters (Per Domain)

• Transaction Timeout Seconds
• Default number of seconds for transaction
  timeout, unless overridden by API call or EJB
  container
• Abandon Timeout Seconds
• After X number of seconds, stop trying to resolve
  branch(es) of a committed transaction and log an
  error
• Should never happen unless resource dies during
  commit processing and does not come back
• Forget Heuristics
• When resource reports a heuristic completion, log
  an error message and then tell resource to
  forgetabout that transaction

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Configuration Parameters (Per Domain)

• Before Completion Iteration Limit
• Maximum number of times a server will iterate
  through registered Synchronization objects for
  the same transaction
• Prevents infinite loops when one Synchronization
  callback causes another Synchronization object
  registration
• Max Transactions
• Maximum number of transactions that can be
  simultaneously active on a server
• Max Unique Name Statistics
• Maximum number of transaction names remembered
  for categorizing statistic subtotals

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Configuration Options
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Configuration Parameters (Per Server)

• Transaction Log File Prefix
• Each server that coordinates a two-phase commit
  transaction writes to the transaction log at
  commit time and reads the transaction log during
  crash recovery
• A transaction log is stored in multiple files
• Space is reclaimed automatically
• Never delete these files
• Default location is servers current directory
• Highly reliable file system is recommended (RAID,
  etc.)
• File naming convention
• Prefix ServerName 9999 .tlog (9999
  unique number)

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Configuration Parameters (JDBC)

• Transaction branches
• Connection pool name determines transaction
  branch qualifier
• Different pool names cause separate branches,
  even if connected to same database
• Databases typically provide lock isolation
  between branches, shared locks within a branch
• Benefits of multiple branches
• Lock isolation protects independently developed
  components from unexpected cross-interference
• Drawbacks of multiple branches
• Lock conflicts can cause deadlock/timeout
• More overhead in transaction coordination, more
  XA calls

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Configuration Parameters (JDBC)

• JDBCTxDataSource wrapper for non-XA database
  drivers
• If EnableTwoPhaseCommitfalse (the default) and
  a non-XA JDBC driver is supplied, commit() will
  fail unless this is the only transaction
  participant
• If EnableTwoPhaseCommittrue a non-XA JDBC
  driver may participate in a transaction with
  multiple participants, however there is a risk
  that the non-XA driver might fail at commit time
• This is reported as a heuristic rollback exception

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Monitoring

• Counters
• Overall
• Subtotal by XAResource
• Subtotal by Transaction name
• Specific transactions
• List transactions more than XX seconds old
• Old transactions are the most interesting ones

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Monitoring Summary
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Monitoring Stats by Name
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Monitoring Stats by Resource
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Monitoring Individual Transactions
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Coming Attractions

• Ongoing integration testing and cooperation with
  XA resource providers
• Support for transaction export/import to/from
  external systems via interposed gateway
  architecture
• Additional internal enhancements for reliability,
  overload tolerance, and performance
• Additional management, monitoring, statistics

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References

• Specifications
• http//www.java.sun.com/products/jta
• http//www.java.sun.com/j2ee
• BEA WebLogic Server 6.0 Documentation
• http//e-docs.bea.com
• News Group
• news//newsgroups.bea.com/weblogic.developer.inter
  est.transaction

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Questions Answers
QA