c优化Oracle 19C数据库，推动EMC卓越性能（oracle19c em）

C优化Oracle 19C数据库，推动EMC卓越性能

在今天的企业应用环境中，Oracle数据库是非常常见并且很重要的一项技术。然而，在高压的业务环境下，如何优化Oracle数据库的性能是每个DBA都需要面临的问题。为了进一步推动企业核心库Oracle数据库的卓越性能和可靠稳定性，本文将介绍如何通过一些C语言优化Oracle 19C数据库，以实现EMC的更好的性能。

1. 使用C语言优化SQL性能

在实际的开发中，往往会有大量的SQL查询语句，尤其是复杂的业务系统中，查询操作是非常耗时的。在这种情况下，我们可以利用C语言进行优化。通过C程序从数据库中获取数据，去掉复杂的查询条件，可以有效地提高查询速度。下面是一个使用C语言查询Oracle数据库的例子：

#include 
#include 
#include 
int mn(void)
{
    OCIEnv *envhp;
    OCIError *errhp;
    OCIServer *srvhp;
    OCISession *authp;
    OCISvcCtx *svchp;
    OCISessionPool *poolhp;
    OCIServerAttach *p_attach;

    OCIStmt *stmthp;
    OCIDefine *defhp;
    char tmp[200];
    char tk[4][30];
    char out[200];

    sword ret;
    ub2 colcnt;
    ub2 rowcnt;
    ub2 i;
    OCIInitialize(OCI_DEFAULT, (dvoid *)0, (dvoid * (*)())0,(dvoid * (*)())0,  (void (*)())0 );
    OCIHandleAlloc((dvoid *)0, (dvoid **)&envhp, OCI_HTYPE_ENV, 0, (dvoid **)0);
    OCIHandleAlloc((dvoid *)envhp, (dvoid **)&errhp, OCI_HTYPE_ERROR, 0, (dvoid **)0);
    OCIHandleAlloc((dvoid *)envhp, (dvoid **)&srvhp, OCI_HTYPE_SERVER, 0, (dvoid **)0);
    OCIHandleAlloc((dvoid *)envhp, (dvoid **)&authp, OCI_HTYPE_SESSION, 0, (dvoid **)0);
    OCIHandleAlloc((dvoid *)envhp, (dvoid **)&svchp, OCI_HTYPE_SVCCTX, 0, (dvoid **)0);
    OCIHandleAlloc((dvoid *)envhp, (dvoid **)&poolhp, OCI_HTYPE_SESSIONPOOL, 0, (dvoid **)0);

    OCIServerAttach(srvhp, errhp, (text *)"http://oracle19c.com:1521/orcl19c", strlen("http://oracle19c.com:1521/orcl19c"), OCI_DEFAULT);
    OCISessionBegin(svchp, errhp, authp, OCI_CRED_RDBMS, OCI_DEFAULT);
    OCISessionPoolCreate( envhp, errhp, poolhp, (CONST OraText*) "jdbc:oracle:thin:@oracle19c.com:1521:orcl19c", strlen("jdbc:oracle:thin:@oracle19c.com:1521:orcl19c"), (CONST OraText*) "teyota", strlen("teyota"), (CONST OraText*) "teyota", strlen("teyota"), 0, 0, 0, 0, 0, 0, 0, OCI_DEFAULT );

    OCIHandleAlloc((dvoid *)envhp, (dvoid **)&stmthp, OCI_HTYPE_STMT, 0, (dvoid **)0);

    sprintf(tmp, "SELECT * FROM EMP WHERE JOB = :1");
    OCIStmtPrepare(stmthp, errhp, (text*)tmp, strlen(tmp), OCI_NTV_SYNTAX, OCI_DEFAULT);
    for(i=0; i
        ret = OCIDefineByPos(stmthp, &defhp, errhp, i+1, out, 30, SQLT_STR, 0, 0, 0, OCI_DEFAULT);
    }

    sprintf(tk[0], "%s", "CLERK");
    OCIBindByName(stmthp, &defhp, errhp, (text*) ":1", -1, &tk[0], strlen(tk[0])+1, SQLT_STR, 0, 0, 0, 0, 0, OCI_DEFAULT);
    OCIStmtExecute(svchp, stmthp, errhp, 1, 0, 0, 0, OCI_DEFAULT);

    OCIAttrGet(stmthp, OCI_HTYPE_STMT, (dvoid *)&colcnt, 0, OCI_ATTR_PARAM_COUNT, errhp);

    while((ret = OCIStmtFetch(stmthp, errhp, 1, OCI_DEFAULT, OCI_DEFAULT)) != OCI_NO_DATA)
    {
        for(i=1; i
            OCIDefineGetData(defhp, errhp, i, (dvoid*)out, 30, SQLT_STR, 0);
            printf("%s\t", out);
        }
        printf("\n");
    }
    OCIStmtRelease(stmthp, errhp, (text *)tmp, strlen(tmp), OCI_DEFAULT);

    OCISessionPoolDestroy(poolhp, errhp, OCI_DEFAULT);
    OCISessionEnd(svchp, errhp, authp, OCI_DEFAULT);
    OCIServerDetach(srvhp, errhp, OCI_DEFAULT);

    OCIHandleFree((dvoid *)envhp, OCI_HTYPE_ERROR);
    OCIHandleFree((dvoid *)envhp, OCI_HTYPE_SERVER);
    OCIHandleFree((dvoid *)envhp, OCI_HTYPE_SESSION);
    OCIHandleFree((dvoid *)envhp, OCI_HTYPE_SVCCTX);
    OCIHandleFree((dvoid *)envhp, OCI_HTYPE_SESSIONPOOL);
    OCIHandleFree((dvoid *)envhp, OCI_HTYPE_STMT);
    OCIHandleFree((dvoid *)envhp, OCI_HTYPE_DEFINE);
    OCIHandleFree((dvoid *)envhp, OCI_HTYPE_DESCRIBE);
    OCIExit();
    return 0;
}

2. 引入缓存技术

当大量用户同时访问Oracle数据库时，往往会造成服务器的负载压力。我们可以使用C语言实现一个简单的缓存技术，让服务器只需从缓存中获取数据，从而减轻数据库的查询压力。下面是一个简单的缓存实现方法：

#include 
#include 
#include 
#include 
#define MAX_CACHE_SIZE 1000
#define MAX_KEY_SIZE 100
typedef struct cache {
    char* key;
    int value;
    struct cache *next;
} cache_t;

cache_t* head = NULL;
bool cache_full = false;
void add_cache(char* key, int value) {
    /* check if the key already exists in cache */
    cache_t* ptr = head;
    while(ptr) {
        if(strcmp(ptr->key, key)==0) {
            ptr->value = value;
            return;
        }
        ptr = ptr->next;
    }
    
    /* if cache is full, remove the last node */
    if(cache_full) {
        ptr = head;
        cache_t* last = NULL;
        while(ptr->next) {
            last = ptr;
            ptr = ptr->next;
        }
        free(ptr->key);
        free(ptr);
        last->next = NULL;
    }

    /* add new node to the front of cache */
    cache_t *node = (cache_t*)malloc(sizeof(cache_t));
    node->key = (char*)malloc(strlen(key)+1);
    strcpy(node->key, key);
    node->value = value;
    node->next = head;
    head = node;
}
void clear_cache() {
    cache_t* ptr = head;
    while(ptr) {
        cache_t* next = ptr->next;
        free(ptr->key);
        free(ptr);
        ptr = next;
    }
    head = NULL;
}
int get_cache(char* key) {
    cache_t* ptr = head;
    while(ptr) {
        if(strcmp(ptr->key, key)==0) {
            return ptr->value;
        }
        ptr = ptr->next;
    }
    return -1;
}

使用缓存技术，需要谨慎使用缓存大小和缓存数据的更新策略，需要根据实际的业务环境进行调整和优化。

通过C语言优化Oracle 19C数据库，可以在提高数据库性能，减少服务器负载压力，提高企业核心库稳定性方面，起到非常重要的作用。需要根据实际的业务场景进行具体的优化操作，以实现更好的应用效果。