Why does this code eat so much memory?

// Modified from libpq example code.
// This code is made available under the same license as the original.

// Build commmand:
// gcc -o libpq-bench libpq-bench.c -I`pg_config --includedir` -L`pg_config --libdir` -lpq

#include <stdio.h>
#include <stdlib.h>
#include <libpq-fe.h>

int
main(int argc, char **argv)
{
    const char *conninfo;
    PGconn     *conn;
    PGresult   *res;

    if (argc > 1)
        conninfo = argv[1];
    else
        conninfo = "";

    conn = PQconnectdb(conninfo);

    if (PQstatus(conn) != CONNECTION_OK)
    {
        fprintf(stderr, "Connection to database failed: %s",
                PQerrorMessage(conn));
        PQfinish(conn);
        exit(1);
    }

    int value;
    if (!PQsendQuery(conn, "select generate_series(1, 10000000)"))
    {
        fprintf(stderr, "Send query failed: %s", PQerrorMessage(conn));
        PQfinish(conn);
        exit(1);
    }

    int i, j;
    for (;;) {
        res = PQgetResult(conn);
        if (res == NULL)
            break;
        for (i = 0; i < PQntuples(res); i++) {
            value = atoi(PQgetvalue(res, i, 0));
        }
        PQclear(res);
    }

    printf("%d\n", value);
    PQfinish(conn);
    return 0;
}