C Client Library

• Non-blocking database connection functions
  • Reasonably high connection startup overhead
  • TCP overhead (if applicable)
  
  
  • PGconn *PQconnectStart(const char *conninfo)
    • conninfo as for PQconnectdb()
  • PostgresPollingStatusType PQconnectPoll(PGconn *conn)
    • Check status of connection
    • PGRES_POLLING_READING - waiting for read on socket
    • PGRES_POLLING_WRITING - waiting write on socket
    • PGRES_POLLING_ACTIVE - network connection established, wait for PGRES_POLLING_OK
    • PGRES_POLLING_OK - connection successfully established
    • PGRES_POLLING_FAILED - connection failed

01    #include "libpq-fe.h"
02    #include <stdio.h>
03    
04    #include <sys/time.h>
05    #include <sys/types.h>
06    #include <unistd.h>
07    #include <errno.h>
08    #include <string.h>
09    
10    int main(void)
11    {
12        int i;
13        PGconn *conn;
14        struct timeval tv;
15        fd_set in, out, exp;
16         
17        conn = PQconnectStart("user=swm dbname=template1");
18    
19        if(PQstatus(conn) == CONNECTION_BAD)
20            exit(1);
21    
22        tv.tv_sec = 1;
23        tv.tv_usec = 0;
24    
25        i = 0;
26        while(i&lt;100) {
27            switch(PQconnectPoll(conn)) {
28                case PGRES_POLLING_ACTIVE:
29                    fprintf(stderr,"polling active\n");
30                    break;
31                case PGRES_POLLING_WRITING:
32                    fprintf(stderr,"polling writing\n");
33                    FD_ZERO(&in);
34                    FD_ZERO(&out);
35                    FD_ZERO(&exp);
36                    FD_SET(PQsocket(conn),&out);
37                    FD_SET(PQsocket(conn),&exp);
38                    select(PQsocket(conn) + 1,&in,&out,&exp,&tv);
39                    break;
40                case PGRES_POLLING_READING:
41                    fprintf(stderr,"polling reading\n");
42                    FD_ZERO(&in);
43                    FD_ZERO(&out);
44                    FD_ZERO(&exp);
45                    FD_SET(PQsocket(conn),&in);
46                    FD_SET(PQsocket(conn),&exp);
47                    select(PQsocket(conn) + 1,&in,&out,&exp,&tv);
48                    break;
49                case PGRES_POLLING_OK:
50                    fprintf(stderr,"connection ready\n");
51                    break;
52                case PGRES_POLLING_FAILED:
53                    fprintf(stderr,"failed\n"); exit(1);
54            }
55            i++;
56        }
57        PQfinish(conn);
58    }
59    

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