IBM Informix Developer's Handbook - IBM Redbooks

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ow that has not been committed (this is known as a phantom read) to the database and the data would be lost during a subsequent rollback. Because of potential problems with uncommitted data that is rolled back, use Dirty Read isolation with care. Databases that do not have logging turned on (and thus do not allow transactions) use Dirty Read as a default isolation level. In fact, Dirty Read is the only isolation level allowed for databases that do not have logging turned on. Committed Read isolation Committed Read isolation (or ANSI Read Committed) removes the problem of phantom reads. A reader with this isolation level checks for locks before it returns a row. By checking for locks, the reader cannot return any uncommitted rows. The database server does not actually place any locks for rows read during Committed Read. It simply checks for any existing rows in the internal lock table. Committed Read is the default isolation level for databases with logging, and it is an appropriate isolation level for most activities. Cursor Stability isolation A reader with Cursor Stability isolation acquires a shared lock on the row that is currently fetched. This action assures that no other user can update the row until the user fetches a new row. If you do not use a cursor to fetch data, Cursor Stability isolation behaves in the same way as Committed Read. No locks are actually placed. Repeatable Read isolation Repeatable Read isolation (also known as ANSI Serializable and ANSI Repeatable Read) is the strictest isolation level. With Repeatable Read, the database server locks all rows examined (not just fetched) for the duration of the transaction. Repeatable Read is useful during any processing in which multiple rows are examined, but nothing will change during the transaction. The original application holds a read lock on each account that it examines until the end of the transaction, so the attempt by the second application to change the first account fails (or waits, depending upon SET LOCK MODE). Note: With Repeatable Read, because even examined rows are locked, if the database server reads the table sequentially, a large number of rows unrelated to the query result can be locked. 448 IBM Informix Developer’s Handbook
Use Repeatable Read isolation for tables when the database server can use an index to access a table. If an index exists and the optimizer chooses a sequential scan instead, you can use directives to force use of the index. However, forcing a change in the query path might negatively affect query performance. 13.4 Configuration options We have brought configuration parameters into our discussion several times. In this section, we examine IBM Informix Server configuration options that directly affect application development. We point out what the developers should know, and how these parameters affect the application and transactions. For more information about any of the parameters in the onconfig file or environment variables relating to configuration, see IBM Informix Dynamic Server Administrator's Reference, v11.50, SC27-3607. 13.4.1 Server identification When the Informix server needs to resolve a database instance name, the oninit process uses the contents of a file known as the sqlhosts file. Each line in the sqlhosts file provides a database server naming reference, called the DBSERVERNAME, along with a protocol, a host system reference, and a listening protocol service reference. On Windows systems, this information is stored in the registry and is updated and accessed using the setnet32.exe utility. Multiple DBSERVERNAME references allow for an evenly distributed connection distribution over a variety of protocols In addition to the information in the sqlhosts file, the DBSERVERNAME crosses reference to the onconfig file, which holds the configuration information describing how the database server is to operate. When a client application connects to a database server, it specifies a DBSERVERNAME, which helps the server to know which protocol will be used for the connectivity. The DBSERVERNAME used in the application connection must be consistent with a name specified in the sqlhosts file and a DBSERVERNAME that is defined in the onconfig file. In the onconfig file, there is a default (main instance) DBSERVERNAME and one or more alternate DBSERVERNAME parameters that are available. The DBA specifies the default name to be used with the DBSERVERNAME parameter in the onconfig file. For alternative application processing, the DBA can allow for or specify alternative protocols, referenced by an a different DBSERVERNAME. The alternate DBSERVERNAME or names are specified by the DBSERVERALIASES parameter in the onconfig file. An application developer Chapter 13. Application development considerations 449
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IBM Informix Developer’s Handbook
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Note: Before using this information
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3.2 Setup and configuration . . . .
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8.3.1 Connecting to the database .
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12.5.2 Compiling the wrapper code .
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Trademarks IBM, the IBM logo, and i
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Krishna Doddi (also known as Prasad
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Comments welcome Your comments are
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1.1 Server options There are a numb
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This edition offers the following a
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either an HDR secondary or RSS seco
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There are three edition options for
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functions. An application calls the
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The IBM Data Server Driver for JDBC
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OLEDB Microsoft OLE DB is a specifi
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The DataBlade Developers Kit provid
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1.3.1 Architecture overview An unde
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Physical and logical logging As eac
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Before you select an API or library
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Hidden, behind-the- scenes tasking
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2.1 Server setup In this section, w
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A typical sqlhosts file contains th
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Figure 2-1 shows the Server Informa
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with the existing Informix instance
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2.2 Client setup ► Edit the Infor
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Figure 2-4 illustrates the options
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2. Prepare the environment. You nee
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5. If you selected a Custom install
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At this stage, the Client SDK insta
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You can download some of these comp
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46 IBM Informix Developer’s Handb
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2. On the Software License Agreemen
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5. Verify the installation selectio
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3. Extract the IBM Data Server Driv
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For a silent installation on both W
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Configuring the JDBC driver To use
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3.1 ODBC and Informix ODBC is a sof
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► IBM Informix ODBC Driver (64-bi
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You can set optional configuration
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Parameter Description Insert Cursor
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Table 3-5 shows the ODBC libraries
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Keyword Description DriverODBCVer S
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Keyword Description DESCRIBEDECIMAL
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If there is no database alias defin
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Example 3-5 shows a simple db2cli.i
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The application sends SQL request t
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} 78 IBM Informix Developer’s Han
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SQLSMALLINT DecimalDigits, /* ibSca
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If your application requires only S
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} SQLCHAR sname[15+1]; SQLLEN lcode
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fprintf (stdout, "Connected\n"); 88
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SQLAllocHandle (SQL_HANDLE_ENV, SQL
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SQLAllocHandle (SQL_HANDLE_ENV, SQL
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contains the data or special attrib
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Function Description ifx_lo_specset
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SQLSMALLINT lospec_size; SQLINTEGER
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4. Call ifx_lo_open() to open the s
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SQLBindParameter (hstmt, 1, SQL_PAR
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} SQLFreeHandle (SQL_HANDLE_ENV, he
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SQLCHAR*insertStmt = (SQLCHAR *) "I
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Accessing a complex data type Examp
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C:\work> 3.3.5 Error handling Ludwi
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C:\work>connect_error demo_on;UID=w
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We create a function called CheckDi
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Figure 3-14 shows the Tracing tab.
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Example 3-36 demonstrates how to se
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DRDADEBUG All IBM Data Server drive
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124 IBM Informix Developer’s Hand
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4.1 Informix ESQL/C Informix ESQL/C
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Example 4-1 shows a simple sqlhosts
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Compiling ESQL/C programs The esql
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Platform Environment variable Linux
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Example 4-3 shows a statement that
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:fname[i], :lname[i], :company[i],
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The SELECT statement shown in Examp
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EXEC SQL fetch ex_cursor into :n1,:
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Table 4-3 lists a few ESQL/C data t
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the sbspace in the server before yo
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Example 4-10 shows the ESQL/C comma
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Example 4-12 shows the output of Ex
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} EXEC SQL END DECLARE SECTION; 150
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C->S (16) Time: 2010-07-06 20:21:58
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5.1 JDBC drivers for an Informix da
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5.1.2 IBM Data Server Driver for JD
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Example 5-4 shows the CLASSPATH env
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Example 5-6 shows the compile line
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programmer uses Java data types to
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Example 5-9 shows the syntax of the
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" Connected to Informix Dynamic Ser
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5.4.2 Manipulating data In this sec
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conn.close(); } catch ( Exception e
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Example 5-15 demonstrates how to di
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conn = DriverManager.getConnection(
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con.setAutoCommit(false); Statement
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System.out.format("Last row: \t%d,"
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PreparedStatement pstmt=conn.prepar
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System.err.println(e); } } } Exampl
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Issuer: CN=bedfont.uk.ibm.com, O=ib
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5.6.1 Class not found errors The fo
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5.7.2 IBM Data Server Driver for JD
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6.1 Hibernate for Java This section
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A Hibernate application includes th
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6.2.2 Configuration File Descriptio
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Example 6-3 shows a hibernate.cfg.x
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name="State" table="States">
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Example 6-6 shows the CLASSPATH var
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informix password org.hibernate
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Example 6-11 shows basic Java code
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The only difference between the loa
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1, AZ, Arizona 2, CA, California C:
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Example 6-19 shows the output of th
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private Long id; private String cod
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7.1 IBM Informix OLE DB Provider In
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through COM. You can use it to test
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7.3.1 Supported interfaces An OLE D
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7.3.3 Type mapping Keyword Descript
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7.3.4 Cursors Informix OLE DB Provi
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Example 7-3 demonstrates how to con
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Connect to the Database Server CHEC
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#define CHECK(hr) if (((HRESULT)(hr
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} 232 IBM Informix Developer’s Ha
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if(lDataLength > 0) { // Call GetCh
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_bstr_t bstrPassWord = "password";
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Provider with some of the available
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cx.connectionstring = "Data Source=
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California 0.08250 c:\work> 7.4.3 S
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The user ID for the Informix databa
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happen that the 32-bit provider is
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7.5.2 Tracing Failure when handling
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A44: 53C Exit Object Address: 0x032
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8.1 Informix and .NET data provider
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Both providers have the same assemb
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Example 8-3 shows how to compile an
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Attribute Description Default Exclu
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The majority of the connection stri
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Data Server Provider for .NET type
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Example 8-7 shows the output of Exa
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Table 8-9 lists the methods that th
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Method Description IfxMonthSpan Get
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} } int drows=0; 272 IBM Informix D
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Example 8-16 shows the output of Ex
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Method Description Int64 Seek(offse
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... 280 IBM Informix Developer’s
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IfxConnection conn; IfxClob vclob;
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Property Type Description Year Int3
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Hour : 8 Minute: 20 C:\work>c Arith
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Method Description Compare(IfxDec1,
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C:\work>decimal Value Sales Tax : 0
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Ceiling Sales Tax : 1.0 Negative Sa
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Visual Studio Add-In provides tools
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9.1 Informix and PHP extensions The
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- Console mode Enter one of the fol
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9.2.4 Verifying connectivity You ca
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► Secure Although PHP is open sou
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*--- persistent connect trusted use
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In a web application, the input dat
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Dynamic SQL statements Dynamic SQL
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$stmt->bindValue(':p9', $_POST["pho
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*--- Verification ---*/ $stmt1=$dbc
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$row=$stmt1->fetch(PDO::FETCH_ASSOC
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} /*--- Get the BLOB from the datab
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In Example 9-17 on page 316, the da
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Function Description db2_bind_param
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The IBM_DB2 extension This PHP exte
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9.3.5 Exception handling Error hand
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The error information that is gener
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9.3.6 Troubleshooting printf("NonCr
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10.1 An overview of UDRs and databa
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10.1.2 About UDRs specific examples
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Invoking a UDR You can invoke a UDR
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10.2 Developing UDRs To develop a U
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One variable in, one result out For
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10.2.2 UDRs in Java 5 1005 6 1006 7
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Note: The paths for .jar files that
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We use the following procedure to c
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For our example, JVPCLASSPATH is se
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10.2.3 UDRs in C and break somethin
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3. Set the bld file permissions as
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4. Create the function in dbaccess.
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Installing the DataBlade Any DataBl
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To connect to a database, run one o
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IBM Informix DataBlade module name
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interface, called BladeSmith, allow
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11.1 A brief overview of Ruby on Ra
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The following drivers allow Ruby to
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Data types The Ruby Informix driver
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03/07/2010 17:30 1,088 LICENSE 03/0
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The Rails Adapter can be installed
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server: demo_on username: informix
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Using Ruby Informix driver In this
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If the SQL statement returns only o
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Example 11-17 shows how to select a
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Example 11-19 shows a simple Ruby s
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# create a prepare object stmt = IB
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11.4 Using the Rails Adapter with R
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For more information, refer to: htt
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Figure 11-1 shows the Listing items
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11.5.1 Creating the Rails applicati
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11.5.4 Migrating the model Ruby on
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11.5.5 Starting the Rails web serve
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Page 416 and 417: 12.1 Basic concepts In this section
Page 418 and 419: A web service can perform the follo
Page 420 and 421: Example 12-1 shows a typical shell
Page 422 and 423: 12.3.2 The w4gl utility For additio
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Page 428 and 429: Example 12-8 shows the APP SERVER f
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Page 432 and 433: Source file information Finally, yo
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Page 444 and 445: After this process is complete, the
Page 446 and 447: while using one of the I4GL web ser
Page 448 and 449: Keeping the wrapper C files in the
Page 450 and 451: 12.6.2 Tracing A developer can use
Page 454 and 455: 13.1 Concurrency and locking 13.1.1
Page 456 and 457: 13.1.2 Lock duration The length of
Page 458 and 459: If a table is not created with row
Page 460 and 461: How the database server manages byt
Page 462 and 463: 13.2.1 Deadlocks reader can read a
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Page 468 and 469: Note: For information about writing
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Page 472 and 473: The DIRECTIVES parameter The DIRECT
Page 474 and 475: 13.5 Working with your database adm
Page 476 and 477: ► Metadata updates affect logging
Page 478 and 479: Guidelines for setting VPCLASS: ►
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Page 484 and 485: area of specific interest. The func
Page 486 and 487: B.1 Distributed transactions A tran
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Page 490 and 491: } { printf("XA_PREPARE failed with
Page 492 and 493: When using distributed transactions
Page 496 and 497: Online resources ► IBM Informix D
Page 498 and 499: cast function 332 cast support func
Page 500 and 501: IfxDecimal public method 287 ifxdot
Page 502 and 503: jvpjavavm 341 jvplog 347 jvplogfile
Page 504 and 505: sql_longvarbinary 80, 96 sql_longva
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