Transactions in HFSQL Client/Server mode

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Transactions in HFSQL Client/Server mode

Available only with this kind of connection

Overview

To keep maximum compatibility between HFSQL Classic applications (single-user or multi-user) and HFSQL Client/Server applications, the transaction mechanism in HFSQL Client/Server mode is similar to the one in HFSQL Classic mode.

This help page presents the differences between the operating modes.

See The transactions for more details.

Remark: From version 19, HFSQL is the new name of HyperFileSQL.

Principle

Principle of transactions on HFSQL Client/Server files and on HFSQL Classic files

Each write operation performed during a transaction is stored in a transaction file. The transaction can be canceled at any time: all operations performed since the beginning of transaction will be canceled.

The transaction is automatically canceled:

when a fatal error occurs in the program (the application is closed).
during the call to EndProgram.
when the test mode is stopped from the editor.
when a power failure occurs or when the application is shut down unexpectedly.
when the connection is lost or closed by the client.
when the server is restarted. Caution: the transaction is not canceled if a secured password is assigned to the file involved in the transaction. The transaction will be canceled during the next opening of the data file.

Versions 19 and later
Isolation of transactions
The HFSQL engine proposes to isolate the transactions: the modifications performed in a transaction in progress are isolated from the ones performed in the other transactions run simultaneously, until it is committed.

Several isolation modes are available:

"READ UNCOMMITTED": Read uncommitted data (default mode).
"READ COMMITTED": Read committed data.
"REPEATABLE READ": Snapshot transactions

See Isolation of transactions for more details.

New in version 19
Isolation of transactions
The HFSQL engine proposes to isolate the transactions: the modifications performed in a transaction in progress are isolated from the ones performed in the other transactions run simultaneously, until it is committed.

Several isolation modes are available:

"READ UNCOMMITTED": Read uncommitted data (default mode).
"READ COMMITTED": Read committed data.
"REPEATABLE READ": Snapshot transactions

See Isolation of transactions for more details.

Isolation of transactions
The HFSQL engine proposes to isolate the transactions: the modifications performed in a transaction in progress are isolated from the ones performed in the other transactions run simultaneously, until it is committed.

Several isolation modes are available:

"READ UNCOMMITTED": Read uncommitted data (default mode).
"READ COMMITTED": Read committed data.
"REPEATABLE READ": Snapshot transactions

See Isolation of transactions for more details.

Advanced management

Files created by a transaction

Several types of HFSQL data files are created when the transactions are implemented:

the log of operations in transaction: File in HFSQL format containing the different operations performed on the application files taken into account by the transaction. This file is created by HTransactionStart (or HTransaction). It is named TRSOPERATION.TRS.
the identification log: File containing information used to identify the transaction (name of the client, computer, ...). This file is named TRSOperationInfoClient.TRS.
the log of values: File associated with each data file taken into account by the transaction. This file is named <FileName>.TRX. For each operation performed in the transaction, this file contains:
- the content of the record after the operation (during a deletion for example).
- the content of the record after the operation (during an addition for example).

Organization of files on the server

1. __TRS directory
This directory contains:

The log of operations in transaction.
The identification log
For each data file in transaction of each database, the corresponding file of values. The tree structure used corresponds to the tree structure of the data files associated with the database.

For example, if the Orders file of DataApplicationA is in transaction, the __TRS\DataApplicationA subdirectory will contain the Orders.TRX file.
Another example: if the Customer file of DataApplicationB is in transaction, the __TRS\DataApplicationB\Customer subdirectory will contain the Customer.TRX file.
2. Database directory DataApplicationA
3. Database directory DataApplicationB

Identifier of the computer that performs the transaction

The computer that performs the transaction is identified according the same method in HFSQL Classic and in HFSQL Client/Server: By default, the computer is identified by a unique number and by the computer name (defined in Windows).

To easily identify the computer that performs the operations in transaction, HComputer allows you to define an identifier specific to the computer. This identifier replaces the computer name. This identifier is saved in the log of operations in transaction and it can be consulted via the HFSQL Control Center.

The client is identified by:

HComputer (identical to HFSQL Classic).
Name and IP address of computer.
Name of the application, that is ExecutableName (ProjectName).

This information can be retrieved by HTransactionInterrupted if the transaction is interrupted.

Errors specific to the management of transactions in HFSQL Client/Server mode

74020: The password of the transaction file does not correspond to the password of the source file
The data file (in HFSQL Client/Server mode) and the transaction file do not use the same password.

Versions 19 and later
70032: Problem of isolation mode
This error can occur in the following cases:

You are trying to use HTransactionIsolation on data files that are not in Client/Server format.
You are trying to use an isolation mode while the transaction is not performed on a connection.
You are trying to use HTransactionIsolation while the transaction was already started by HTransactionStart (or HTransaction).

New in version 19
70032: Problem of isolation mode
This error can occur in the following cases:

You are trying to use HTransactionIsolation on data files that are not in Client/Server format.
You are trying to use an isolation mode while the transaction is not performed on a connection.
You are trying to use HTransactionIsolation while the transaction was already started by HTransactionStart (or HTransaction).

70032: Problem of isolation mode
This error can occur in the following cases:

You are trying to use HTransactionIsolation on data files that are not in Client/Server format.
You are trying to use an isolation mode while the transaction is not performed on a connection.
You are trying to use HTransactionIsolation while the transaction was already started by HTransactionStart (or HTransaction).

Related Examples:

Training (WINDEV): WD Transaction

[ + ] This program, powered by WINDEV, is based on a simplified analysis (ORDERS, ORDERLINE and STOCK). It illustrates the operating mode of the transactions when placing an order.