pgpool分析三

pgpool一共可以管理pool_config->num_init_children * pool_config->max_pool * sizeof(ConnectionInfo);数据库连接

每个pool_config->num_init_children 对应pgpool的一个child进程，也就是对应一台postgresql数据库，这个进程最多可以管理pool_config->max_pool个对数据库的连接

数据库的连接主要就是记录数据库名，用户名之类的

/*
* Connection pool information. Placed on shared memory area.
*/
typedef struct {
char   database[SM_DATABASE]; /* Database name */
char   user[SM_USER]; /* User name */
int    major; /* protocol major version */
int    minor; /* protocol minor version */
int    pid; /* backend process id */
int    key; /* cancel key */
int    counter; /* used counter */
time_t    create_time; /* connection creation time */
int load_balancing_node; /* load balancing node */
} ConnectionInfo;

每个child进程保存在共享内存中的信息

/*
* process information
* This object put on shared memory.
*/
typedef struct {
pid_t pid; /* OS's process id */
time_t start_time; /* fork() time */
ConnectionInfo *connection_info; /* head of the connection info for this process ,指向共享内存中的 i * pool_config->max_pool处， */
} ProcessInfo;

以上两个结构是在main进程中初始化，放入共享内存的，对于每一个child进行的连接池

pool_connection_pool = (POOL_CONNECTION_POOL *)malloc(sizeof(POOL_CONNECTION_POOL)*pool_config->max_pool);

typedef struct {
ConnectionInfo *info;   /* connection info on shmem ，指向ProcessInfo->connection_info,从那开始的max_pool个*/
    POOL_CONNECTION_POOL_SLOT *slots[MAX_NUM_BACKENDS];
} POOL_CONNECTION_POOL;

typedef struct {
StartupPacket *sp; /* startup packet info 估计是postgresql的通训协议中要用到的*/
    int pid; /* backend pid */
    int key; /* cancel key */
    POOL_CONNECTION *con;
time_t closetime; /* absolute time in second when the connection closed
       * if 0, that means the connection is under use.
       */
} POOL_CONNECTION_POOL_SLOT;

/*
* stream connection structure
*/
typedef struct {
int fd;   /* fd for connection 直正连接socket，可以是unix domain socket或是inet domain socket */

char *wbuf; /* write buffer for the connection */
int wbufsz; /* write buffer size */
int wbufpo; /* buffer offset */

#ifdef USE_SSL
SSL_CTX *ssl_ctx; /* SSL connection context */
SSL *ssl; /* SSL connection */
#endif
int ssl_active; /* SSL is failed if < 0, off if 0, on if > 0 */

char *hp; /* pending data buffer head address */
int po;   /* pending data offset */
int bufsz; /* pending data buffer size */
int len; /* pending data length */

char *sbuf; /* buffer for pool_read_string */
int sbufsz; /* its size in bytes */

char *buf2; /* buffer for pool_read2 */
int bufsz2; /* its size in bytes */

int isbackend;   /* this connection is for backend if non 0 */
int db_node_id;   /* DB node id for this connection */

char tstate;   /* transaction state (V3 only) */

/*
* following are used to remember when re-use the authenticated connection
*/
int auth_kind;   /* 3: clear text password, 4: crypt password, 5: md5 password */
int pwd_size;   /* password (sent back from frontend) size in host order */
char password[MAX_PASSWORD_SIZE];   /* password (sent back from frontend) */
char salt[4];   /* password salt */

/*
* following are used to remember current session paramter status.
* re-used connection will need them (V3 only)
*/
ParamStatus params;

int no_forward;   /* if non 0, do not write to frontend */

char kind; /* kind cache */

/*
* frontend info needed for hba
*/
int protoVersion;
SockAddr raddr;
UserAuth auth_method;
char *auth_arg;
char *database;
char *username;
} POOL_CONNECTION;

POOL_CONNECTION主要是在socket连接之间缓存的作用，socket写入时先写入wbuf，读入也是先读进rbuf中，之后需要的时候再解析