开启连接池

前提条件：数据源已配置成功。Linux系统请参考Linux下配置数据源；Windows系统请参考Windows下配置数据源。

在Linux和Windows环境下开启连接池，对于需要频繁建立和断开连接的中间层应用程序可显著提升性能，参考配置请参见连接池场景，示例代码如下：

#ifdef WIN32
#include <windows.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <sql.h>
#include <sqlext.h>
#include <string.h>
#include <sys/time.h>
#include <pthread.h>
#include <sqltypes.h>
#include <time.h>
SQLHENV env;
SQLHDBC conn;
struct timeval start, end;

#define CONN_COUNT 15000
#define CHECK_ERROR(retcode, str, handle, htype)                          \
    ({                                                                    \
        if (retcode != SQL_SUCCESS && retcode != SQL_SUCCESS_WITH_INFO) { \
            fprintf(stderr, "FAILED:\t");                                 \
            extract_error(str, handle, htype);                            \
            exit(-1);                                                     \
        } else {                                                          \
            printf("OK:\t%s\n", str);                                     \
        }                                                                 \
    })

void print_diag(char *msg, SQLSMALLINT htype, SQLHANDLE handle)
{
    char sqlstate[32];
    char message[1000];
    SQLINTEGER nativeerror;
    SQLSMALLINT textlen;
    SQLRETURN ret;

    if (msg) {
        printf("%s\n", msg);
    }

    ret = SQLGetDiagRec(htype, handle, 1, sqlstate, &nativeerror, message, 256, &textlen);

    if (ret != SQL_ERROR) {
        printf("%s=%s\n", (CHAR *)sqlstate, (CHAR *)message);
    }
}

void extract_error(char *fn, SQLHANDLE handle, SQLSMALLINT type)
{
    SQLINTEGER i = 0;
    SQLINTEGER NativeError;
    SQLCHAR SQLState[7];
    SQLCHAR MessageText[256];
    SQLSMALLINT TextLength;
    SQLRETURN ret;

    fprintf(stderr, "The driver reported the following error %s\n", fn);
    if (NULL == handle)
        return;
    do {
        ret = SQLGetDiagRec(type, handle, ++i, SQLState, &NativeError, MessageText, sizeof(MessageText), &TextLength);
        if (SQL_SUCCEEDED(ret)) {
            printf("[SQLState:%s]:[%ldth error]:[NativeError:%ld]: %s\n",
                SQLState,
                (long)i,
                (long)NativeError,
                MessageText);
        }
    } while (ret == SQL_SUCCESS);
}

void InitializeEnvironment()
{
    
    /* Windows配置连接池参数，需要在分配环境句柄前完成，此处为开启连接池 */
    SQLSetEnvAttr(env, SQL_ATTR_CONNECTION_POOLING, (SQLINTEGER *)SQL_CP_ONE_PER_DRIVER, 0);

    /* 在Win上关闭连接池 */
    // SQLSetEnvAttr(env, SQL_ATTR_CONNECTION_POOLING, (SQLINTEGER*)SQL_CP_OFF, 0);
    
    // 分配环境句柄
    SQLAllocHandle(SQL_HANDLE_ENV, SQL_NULL_HANDLE, &env);
    // 配置ODBC版本
    SQLSetEnvAttr(env, SQL_ATTR_ODBC_VERSION, (SQLPOINTER)SQL_OV_ODBC3, 0);
    // 配置建连超时时间
    SQLSetConnectAttr(conn, SQL_LOGIN_TIMEOUT, (SQLPOINTER *)5, 0);
}

void test_connect()
{
    SQLRETURN ret;
    SQLCHAR str[1024];
    SQLSMALLINT strl;
    SQLCHAR dsn[1024];
    SQLUINTEGER uIntVal;

    SQLAllocHandle(SQL_HANDLE_DBC, env, &conn);

    /* 根据场景需要调整连接串 */
    char *config = "Driver=GaussMPP;DSN=gaussdb;";
    ret = SQLSetConnectAttr(conn, SQL_ATTR_AUTOCOMMIT, (SQLPOINTER)(1), 0);

    ret = SQLDriverConnect(conn, 0, (SQLCHAR *)config, SQL_NTS, (SQLCHAR *)NULL, SQL_NTS, 0, SQL_DRIVER_NOPROMPT);

    if (SQL_SUCCEEDED(ret)) {
        // printf("Connected\n");
    } else {
        print_diag("SQLDriverConnect failed.", SQL_HANDLE_DBC, conn);
        SQLFreeHandle(SQL_HANDLE_DBC, conn);
        SQLFreeHandle(SQL_HANDLE_ENV, env);
        exit(1);
    }

    /* 将连接放入连接池以重用连接 */
    if (conn != SQL_NULL_HDBC) {
        SQLDisconnect(conn);
        SQLFreeHandle(SQL_HANDLE_DBC, conn);
        conn = SQL_NULL_HDBC;
    }
}

int main()
{
    int count = 0;
    int timeuser;
    gettimeofday(&start, NULL);
    InitializeEnvironment();

    for (int i = 0; i < CONN_COUNT; i++) {
        test_connect();
        count++;
    }

    //释放环境句柄
    SQLFreeHandle(SQL_HANDLE_ENV, env);
    printf("Connection count: %d\n", count);
    gettimeofday(&end, NULL);
    timeuser = 1000000 * (end.tv_sec - start.tv_sec) + end.tv_usec - start.tv_usec;
    printf("Connection time: %.3f s \n", (double)timeuser / 1000000);
    return 0;
}

不同环境下结果不一，在连接池打开的情况下，本示例运行结果如下：

Connection count: 15000
Connection time: 14.175 s

在连接池关闭的情况下，本示例运行结果如下：

Connection count: 15000
Connection time: 691.768 s

Windows环境应用代码同Linux环境如上，连接串需根据场景进行配置。