MapGuide RFC 78 - Enhance transaction capability to Feature Service

This page contains an change request (RFC) for the MapGuide Open Source project. More MapGuide RFCs can be found on the RFCs page.

Status

RFC Template Version	(1.0)
Submission Date	(Date/Time submitted)
Last Modified	(Klain Qin) (Thu Jul 9 22:18:19 2009)
Author	(Klain Qin)
RFC Status	(ready for review)
Implementation Status	(pending)
Proposed Milestone	(2.2)
Assigned PSC guide(s)	(Tom Fukushima)
Voting History	(vote date)
+1
+0
-0
-1
no vote

Overview

This proposal is to enhance the transaction capability of MapGuide Feature Service to support executing not only a sequence of standard commands(delete/update/insert) but also a sequence of sql statements within a single transaction.

Motivation

Currently MapGuide Feature Service supports executing a sequence of standard commands within a single transaction through the API illustrated below. The standard commands are delete/update/insert. If you pass in true for useTransaction, the API will start a transaction and commit(or rollback) it at the end. Thus all command execution will reside inside a single transaction.

virtual MgPropertyCollection* UpdateFeatures( MgResourceIdentifier* resource,
                                              MgFeatureCommandCollection* commands,
                                              bool useTransaction ) = 0;

However, MapGuide Feature Service also provides another two APIs to execute sql statements as illustrated below, where a database transaction will internally be started and committed before and after the sql statement execution. Here the capability of executing a sequence of sql statements within a single transaction is missing.

virtual MgSqlDataReader* ExecuteSqlQuery(MgResourceIdentifier* resource,
                                         CREFSTRING sqlStatemen) = 0;
virtual INT32 ExecuteSqlNonQuery( MgResourceIdentifier* resource,
                                  CREFSTRING sqlNonSelectStatement ) = 0;

This proposal is to expose a seperate transaction control from Feature Service to enable executing a sequence of sql statements within a single transaction.

Proposed Solution

A new class of MgTransaction will be added to represent a transaction to be performed in a data store.

/// \brief
/// MgTransaction represents a transaction to be performed in a DataStore.
/// If the transaction is time out, commit or rollback a transaction will
/// result in one exception MgFeatureServiceException thrown.
class MgTransaction : public MgGuardDisposable
{
PUBLISHED_API:
    /// \brief
    /// Commit the transaction.
    ///
    virtual void Commit() = 0;

    /// \brief
    /// Rollback the transaction.
    ///
    virtual void Rollback() = 0;

    /// \brief
    /// Get the identifier of feature source associated with the transaction.
    ///
    /// \return
    /// Returns the identifier of feature source associated with the transaction.
    ///
    virtual MgResourceIdentifier* GetFeatureSource() = 0;
};

Changes to Feature Service

ExecuteSqlQuery() and ExecuteSqlNonQuery() must use the same underlying connection on which the transaction started. So MgTransaction instance is passed in as parameters for both of these two methods. The MgTransaction implementation can return the undelying connection.

/// \brief
/// Provides an abstraction layer for the storage and retrieval
/// of feature data in a technology-independent way. The API
/// lets you determine what storage technologies are available
/// and what capabilities they have. Access to the storage
/// technology is modeled as a connection. For example, you can
/// connect to a file and do simple insertions or connect to a
/// relational database and do transaction-based operations.
class MgFeatureService : public MgService 
{
PUBLISHED_API:
    /// \brief
    /// Begins a transaction and return it.
    ///
    /// \param resource (MgResourceIdentifier)
    /// A resource identifier referring to a feature source.
    ///
    /// \return
    /// Returns an MgTransaction instance.
    ///
virtual MgTransaction* BeginTransaction(MgResourceIdentifier* resource) = 0;

virtual MgSqlDataReader* ExecuteSqlQuery(MgResourceIdentifier* resource,
                                         CREFSTRING sqlStatemen
                                         MgTransaction* transaction) = 0;

virtual INT32 ExecuteSqlNonQuery( MgResourceIdentifier* resource,
                                  CREFSTRING sqlNonSelectStatement,
                                  MgTransaction* transaction) = 0;
};

One example using the new API

MgTransaction tran = nullptr;
try
{
    tran = MgFeatureService.StartTransaction(resourceId);
    MgFeatureService.ExecuteSql(resourceId, sql statement1, tran); 
    MgFeatureService.ExecuteSql(resourceId, sql statement2, tran); 
    tran.Commit();
}
catch(...)
{
    tran.Rollback();
}

Timeout configuration for MgTransaction

As the transaction is a critical resource for database applications, a server-side transaction can be left open while the application is doing other things in between sql or even worse the application may fail or hang and the server would not know. So it needs to set a timeout for all transactions. If a transaction hasn't been committed or rollbacked within the timeout, the server will automatically rollback the transaction. If you call Commit() or Rollback() on the MgTransaction instance after timeout, an exception will be thrown reminding that the transaction has been timeout and reverted.

Two items will be added into serverconfig.ini for transaction timeout setting. If the transaction hasn't been committed or rollbacked within 2 minutes, it will be automatically rollbacked.

DataTransactionTimeout             = 600
DataTransactionTimerInterval       = 60

Bind MgTransaction to FDO connection

The transaction has to be bound with the underlying FDO connection where it starts during its life circle. The underlying FDO connection will be kept used by the transaction until the call of either Commit() or Rollback(). The implementation of MgTransaction should be able to return the underlying connection.

Implications

This is a new API, so API documentation need to be updated. However, it will not affect the existing application if you don't use it at all.

This new API is designed for sql statement execution. You have to use the API with ExecuteSqlQuery() or ExecuteSqlNonQuery() within the transaction.

Test Plan

A new unit test similar to the above example will be added into the existing Feature Service unit tests.

Funding/Resources

Supplied by Autodesk.