- The document discusses transactions in BEA WebLogic Server 6.0, including how transactions provide data consistency and monitoring/management capabilities. It outlines benefits such as timeouts, monitoring by transaction name, and overload protection. - It describes how multiple servers and resources can participate in distributed transactions using XA. Programming interfaces for transactions are discussed as well as BEA WebLogic extensions. - Configuration parameters for transactions are outlined pertaining to timeouts, transaction logs, and more. Monitoring capabilities like counters and viewing individual transactions are also summarized.

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Weblogic IntroductionWeblogic Introduction

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

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Benefit #1: Data ConsistencyBenefit #1: Data Consistency
• Ensure data integrity when accessing more than
one data store, especially in distributed
environment
• Simple model for application programmer:
AA - atomic
CC - consistent
II - isolated
DD - durable

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Benefit #2: Monitoring & ManagementBenefit #2: Monitoring & Management
• A transaction is a higher-level unit of work than a
database query or an object invocation
o BEA WebLogic Server allows transactions to be given a semantic name
(“TransferFunds” or “ReserveSeat” or “CheckOut”)
o Transaction Name is reported in error messages
o Statistics subtotals categorized by Transaction Name

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Benefit #3: Timeouts & Overload ProtectionBenefit #3: Timeouts & Overload Protection
• Transactions are subject to timeout
o 30 second default
• Application code (or the EJB container) can mark a
transaction “rollback only”
• In an overloaded system, BEA WebLogic Server:
o Times out requests (who waits 30+ seconds for a Web page to return?)
o Avoids wasted work on “doomed” transactions
o Eventually refuses to begin new transactions when there are too many
already running (configurable parameter)

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

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

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High-Level ArchitectureHigh-Level Architecture
Transaction
Manager
XA-Capable
Resource
EJB Container
Application
JDBC
WrapperJTA
JDBC
JMS
XA
JDBC
JTA

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

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

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

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

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Configuration OptionsConfiguration Options

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Configuration Parameters (Per Server)Configuration Parameters (Per Server)
• Transaction Log File Prefix
o 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
o A transaction log is stored in multiple files
• Space is reclaimed automatically
• Never delete these files
o Default location is server’s current directory
o Highly reliable file system is recommended (RAID, etc.)
o File naming convention:
Prefix + ServerName + 9999 + “.tlog” (9999 = unique number)

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Configuration Parameters (JDBC)Configuration Parameters (JDBC)
• Transaction branches
o Connection pool name determines transaction branch qualifier
o Different pool names cause separate branches, even if connected to
same database
o Databases typically provide lock isolation between branches, shared
locks within a branch
o Benefits of multiple branches:
• Lock isolation protects independently developed components from
unexpected cross-interference
o 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)Configuration Parameters (JDBC)
• JDBCTxDataSource wrapper for non-XA database
drivers
o If EnableTwoPhaseCommit=“false” (the default) and a non-XA JDBC driver
is supplied, commit() will fail unless this is the only transaction participant
o If EnableTwoPhaseCommit=“true” 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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MonitoringMonitoring
• Counters
o Overall
o Subtotal by XAResource
o Subtotal by Transaction name
• Specific transactions
o List transactions more than XX seconds old
o “Old” transactions are the most interesting ones

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Monitoring SummaryMonitoring Summary

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Monitoring Stats by NameMonitoring Stats by Name

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Monitoring Stats by ResourceMonitoring Stats by Resource

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Monitoring Individual TransactionsMonitoring Individual Transactions

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Coming AttractionsComing 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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