Using ODBC to Connect to a Cluster

DWS allows you to use an ODBC application to connect to a database through an ECS on the Huawei Cloud platform or a public network address over the Internet.

For details about how to use the ODBC API, see the official document.

Application Scenarios

You want to use an application running on an ECS to access data in a DWS cluster through an ODBC API.
You have developed an application using standard ODBC APIs and want to adapt to multiple databases through a unified API.

Prerequisites

You have downloaded ODBC driver packages dws_x.x.x_odbc_driver_for_xxx.zip (for Linux) and dws_odbc_driver_for_windows.zip (for Windows). For details, see Downloading the JDBC or ODBC Driver.
DWS also supports open source ODBC driver: PostgreSQL ODBC 09.01.0200 or later.
You have downloaded the open-source unixODBC code file 2.3.0 from https://sourceforge.net/projects/unixodbc/files/unixODBC/2.3.0/unixODBC-2.3.0.tar.gz/download.
You have downloaded the SSL certificate file. For details, see Downloading an SSL Certificate.

Notes and Constraints

ODBC APIs do not provide the database connection retry capability. You need to implement the connection retry capability in the service code.
DWS does not support the verify-full mode. Do not set it in the data source configuration.
Keep the private key in the SSL certificate file secure to prevent leakage.

Using an ODBC Driver to Connect to a Database (Linux)

Upload the ODBC package and code file to the Linux environment and decompress them to the specified directory.
Log in to the Linux environment.
Prepare unixODBC.
1. Decompress the unixODBC code file.
```
tar -xvf unixODBC-2.3.0.tar.gz
```
2. Compile the code file and install the driver.
  1 2 3 4
  
  cd unixODBC-2.3.0 ./configure --enable-gui=no --prefix=[your_path] make make install
  - In the command, [your_path] indicates the installation path, which can be specified as required. It must be an absolute path.
  - To perform compilation on an Arm server, add the configure parameter. An example command is as follows:
```
./configure --enable-gui=no --prefix=[your_path] --build=aarch64-unknown-linux-gnu
```
  - After unixODBC is compiled and installed, the *.so.2 library file will be in the installation directory. To create the *.so.1 library file, change LIB_VERSION in the configure file to 1:0:0.
    1
    
    LIB_VERSION="1:0:0"
  - This driver dynamically loads the libodbcinst.so.* library files. If one of the library files is successfully loaded, the library file is loaded. The loading priority is as follows: libodbcinst.so > libodbcinst.so.1 > libodbcinst.so.1.0.0 > libodbcinst.so.2 > libodbcinst.so.2.0.0.
Replace the driver file. (This document uses the dws_8.1.x_odbc_driver_for_x86_redhat.zip package of Red Hat as an example.) The replacement will overwrite the original ODBC driver file. Before performing this operation, ensure that the installation path is correct to prevent any impact on other ODBC applications.
1. Decompress the driver package.
```
unzip dws_8.1.x_odbc_driver_for_x86_redhat.zip
```
2. Copy all files in the lib directory extracted from the driver package to the [your_path]/lib directory.
3. Copy psqlodbcw.la and psqlodbcw.so in the odbc/lib directory extracted from the driver package to the [your_path]/lib/odbc directory.
Run the following command to modify the configuration of the driver file:
```
vi [your_path]/etc/odbcinst.ini
```
Copy the following content to the file:
```
[DWS] 
Driver64=[your_path]/lib/odbc/psqlodbcw.so
```
The parameters are as follows:
- [DWS]: indicates the driver name. You can customize the name.
- Driver64 or Driver: indicates the path where the dynamic library of the driver resides. For a 64-bit operating system, search for Driver64 first. If Driver64 is not configured, search for Driver.

Run the following command to modify the data source file:

vi [your_path]/etc/odbc.ini

Copy the following content to the configuration file, save the modification, and exit.

[DWSODBC]
Driver=DWS
Servername=10.10.0.13
Database=gaussdb
Username=dbadmin
Password=password
Port=8000
Sslmode=allow

Parameter	Description	Example Value
[DSN]	Data source name.	[DWSODBC]
Driver	Driver name. Use the driver name configured in odbcinst.ini.	Driver=DWS
Servername	IP address of the server. When a load balancer is bound to the cluster, set this parameter to the IP address of the load balancer.	Servername=10.10.0.13
Database	Name of the database to be connected to.	Database=gaussdb
Username	Database username.	Username=dbadmin
Password	Database user password.	Password=password
Port	Port number of the server. The default port number of a DWS cluster is 8000.	Port=8000
Sslmode	SSL certification mode. This parameter is enabled for the cluster by default. The SSL mode delivers higher security than the common mode. By default, the SSL function is enabled in a cluster to allow SSL or non-SSL connections from the client. You are advised to use the SSL mode when using ODBC to connect to a DWS cluster. Values and meanings: disable: only tries to establish a non-SSL connection. allow: tries to establish a non-SSL connection first, and then an SSL connection if the first attempt fails. prefer: tries to establish an SSL connection first, and then a non-SSL connection if the first attempt fails. require: only tries to establish an SSL connection. If there is a CA file, perform the verification according to the scenario in which the parameter is set to verify-ca. verify-ca: tries to establish an SSL connection and check whether the server certificate is issued by a trusted CA. verify-full: not supported by DWS	Sslmode=allow

You can view the values of Servername and Port on the DWS console. Log in to the DWS console and choose Clusters > Management > Client Connections from the navigation pane on the left. In the Data Warehouse Connection Information area, select a cluster and obtain its Private Network IP Address or Public Network IP Address. For details, see Obtaining the Connection Address of a DWS Cluster.

Configure environment variables.
```
vi ~/.bashrc
```
Add the following information to the configuration file: It is not recommended to add LD_LIBRARY_PATH in the Kylin OS, as it may cause conflicts with the libssl.so library. The latest cluster versions 8.2.1 and 9.1.0 now provide rpath, which allows dependency libraries to be located without LD_LIBRARY_PATH.
```
export LD_LIBRARY_PATH=[your_path]/lib/:$LD_LIBRARY_PATH 
export ODBCSYSINI=[your_path]/etc 
export ODBCINI=[your_path]/etc/odbc.ini
```
Import environment variables.
```
source ~/.bashrc
```

Run the following commands to connect to the database:

[your_path]/bin/isql -v DWSODBC

If the following information is displayed, the connection is successful:

     +---------------------------------------+ 
| Connected!                            | 
|                                       | 
| sql-statement                         | 
| help [tablename]                      | 
| quit                                  | 
|                                       | 
+---------------------------------------+  
SQL> 
 
 
  

Using an ODBC Driver to Connect to a Database (Windows)

Decompress ODBC driver package dws_odbc_driver_for_windows.zip (for Windows) and install psqlodbc.msi.
Decompress the SSL certificate package to obtain the certificate file.

You have the option to deploy the certificate either automatically or manually, depending on your requirements.
- Automated deployment:
  Double-click the sslcert_env.bat file to trigger automatic deployment of the certificate to a default location. The sslcert_env.bat file ensures the purity of the certificate environment. When the %APPDATA%\postgresql directory exists, a message will be prompted asking you whether you want to remove related directories. If you want to remove the directories, back up the files in the directories.
- Manual deployment:
  - Create a new folder named postgresql in the %APPDATA%\ directory. Before deploying the certificate, ensure that the %APPDATA%\postgresql directory contains no file with the same name as the certificate to prevent the file from being overwritten.
  - Copy files client.crt, client.key, client.key.cipher, and client.key.rand to the %APPDATA%\postgresql directory and change client in the file names to postgres. For example, change client.key to postgres.key. client.key is the private key file of the client. Keep it secure.
  - Copy cacert.pem to %APPDATA%\postgresql and change the name of cacert.pem to root.crt.
Open Driver Manager.

DWS provides 32-bit and 64-bit ODBC drivers. You can choose one that meets your needs. When configuring the data source, use the Driver Manager that matches the bit version of the installed program. (Assume that the OS is installed on drive C. If the OS is installed on another drive, change the path accordingly.)
- If you want to develop 32-bit programs in the 64-bit OS and have installed the 32-bit driver, Open the 32-bit Driver Manager at C:\Windows\SysWOW64\odbcad32.exe. (WoW64 is the acronym for "Windows 32-bit on Windows 64-bit". C:\Windows\SysWOW64\ stores the 32-bit environment in a 64-bit system.)
  Do not choose Control Panel > System and Security > Administrative Tools > Data Sources (ODBC) directly.
- If you want to develop 64-bit programs in the 64-bit OS and have installed the 64-bit driver, open the 64-bit Driver Manager at C:\Windows\System32\odbcad32.exe. (C:\Windows\System32\ stores the environment consistent with the current OS. For technical details, see Windows technical documents.)
  Do not choose Control Panel > System and Security > Administrative Tools > Data Sources (ODBC) directly.
- In a 32-bit OS, open C:\Windows\System32\odbcad32.exe.
  Alternatively, click Computer, and choose Control Panel. Click Administrative Tools and click Data Sources (ODBC).
Configure a data source to be connected to.
1. On the User DSN tab, click Add and choose PostgreSQL Unicode for setup.
  Figure 1 Configuring a data source to be connected to
  
  You can view the values of Server and Port on the DWS console. Log in to the DWS console and choose Clusters > Management > Client Connections from the navigation pane on the left. In the Data Warehouse Connection Information area, select a cluster and obtain its Private Network IP Address or Public Network IP Address. For details, see Obtaining the Connection Address of a DWS Cluster.
2. Click Test. If Connection successful is displayed, the connection is successful.

Compile an ODBC sample program to connect to the data source.

ODBC APIs do not provide the database connection retry capability. You need to implement the connection retry capability in the service code.

The sample code is as follows:

     // This example shows how to obtain DWS data through the ODBC driver.
// DBtest.c (compile with: libodbc.so)  
#include <stdlib.h> 
#include <stdio.h> 
#include <sqlext.h>
#ifdef WIN32
#include <windows.h>
#endif 
SQLHENV       V_OD_Env;        // Handle ODBC environment 
SQLHSTMT      V_OD_hstmt;      // Handle statement 
SQLHDBC       V_OD_hdbc;       // Handle connection     
char          typename[100];
SQLINTEGER    value = 100;
SQLINTEGER    V_OD_erg,V_OD_buffer,V_OD_err,V_OD_id;
int main(int argc,char *argv[]) 
{         
      // 1. Apply for an environment handle.       
      V_OD_erg = SQLAllocHandle(SQL_HANDLE_ENV,SQL_NULL_HANDLE,&V_OD_Env);     
      if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))        
      {           
           printf("Error AllocHandle\n");           
           exit(0);        
      } 
      // 2. Set environment attributes (version information).         
      SQLSetEnvAttr(V_OD_Env, SQL_ATTR_ODBC_VERSION, (void*)SQL_OV_ODBC3, 0);      
      // 3. Apply for a connection handle.        
      V_OD_erg = SQLAllocHandle(SQL_HANDLE_DBC, V_OD_Env, &V_OD_hdbc);     
      if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))      
      {                     
           SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);          
           exit(0);       
      }
      // 4. Set connection attributes.
      SQLSetConnectAttr(V_OD_hdbc, SQL_ATTR_AUTOCOMMIT, SQL_AUTOCOMMIT_ON, 0);          
      // 5. Connect to a data source. You do not need to enter the username and password if you have configured them in the odbc.ini file. If you have not configured them, specify the name and password of the user who wants to connect to the database in the SQLConnect function.
      V_OD_erg = SQLConnect(V_OD_hdbc, (SQLCHAR*) "gaussdb", SQL_NTS,  
                           (SQLCHAR*) "", SQL_NTS,  (SQLCHAR*) "", SQL_NTS);        
      if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))      
      {           
          printf("Error SQLConnect %d\n",V_OD_erg);            
          SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);       
          exit(0);        
      }     
      printf("Connected !\n"); 
      // 6. Set statement attributes.
      SQLSetStmtAttr(V_OD_hstmt,SQL_ATTR_QUERY_TIMEOUT,(SQLPOINTER *)3,0);
      // 7. Apply for a statement handle.
      SQLAllocHandle(SQL_HANDLE_STMT, V_OD_hdbc, &V_OD_hstmt);       
      // 8. Executes an SQL statement directly.
      SQLExecDirect(V_OD_hstmt,"drop table IF EXISTS testtable",SQL_NTS);
      SQLExecDirect(V_OD_hstmt,"create table testtable(id int)",SQL_NTS);
      SQLExecDirect(V_OD_hstmt,"insert into testtable values(25)",SQL_NTS);
      // 9. Prepare for execution.
      SQLPrepare(V_OD_hstmt,"insert into testtable values(?)",SQL_NTS); 
      // 10. Bind parameters.
      SQLBindParameter(V_OD_hstmt,1,SQL_PARAM_INPUT,SQL_C_SLONG,SQL_INTEGER,0,0,
                       &value,0,NULL);
      // 11. Execute the ready statement.
      SQLExecute(V_OD_hstmt);
      SQLExecDirect(V_OD_hstmt,"select c_customer_sk from customer_t1",SQL_NTS);
      // 12. Obtain the attributes of a certain column in the result set.
      SQLColAttribute(V_OD_hstmt,1,SQL_DESC_TYPE,typename,100,NULL,NULL);                 
      printf("SQLColAttribute %s\n",typename);
      // 13. Bind the result set.
      SQLBindCol(V_OD_hstmt,1,SQL_C_SLONG, (SQLPOINTER)&V_OD_buffer,150,
                (SQLLEN *)&V_OD_err);
      // 14. Collect data using SQLFetch.
      V_OD_erg=SQLFetch(V_OD_hstmt);
      // 15. Obtain and return data using SQLGetData.
      while(V_OD_erg != SQL_NO_DATA)
      {
          SQLGetData(V_OD_hstmt,1,SQL_C_SLONG,(SQLPOINTER)&V_OD_id,0,NULL);
          printf("SQLGetData ----ID = %d\n",V_OD_id);
          V_OD_erg=SQLFetch(V_OD_hstmt);
      };
      printf("Done !\n");
      // 16. Disconnect from the data source and release handles.
      SQLFreeHandle(SQL_HANDLE_STMT,V_OD_hstmt);    
      SQLDisconnect(V_OD_hdbc);         
      SQLFreeHandle(SQL_HANDLE_DBC,V_OD_hdbc);       
      SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);  
      return(0);
 }
 
 
  

References

Using ODBC for secondary development: ODBC-Based Development
Example code for ODBC-based development: ODBC Development Example
ODBC APIs: ODBC APIs

Parent Topic: Using the JDBC and ODBC Drivers to Connect to a DWS Cluster

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