PostgreSQL的 initdb 源代码分析之二十四

    make_template0();

/*
 * copy template1 to template0
 */
static void
make_template0(void)
{
    PG_CMD_DECL;
    const char **line;
    static const char *template0_setup[] = {
        "CREATE DATABASE template0;\n",
        "UPDATE pg_database SET "
        "    datistemplate = 't', "
        "    datallowconn = 'f' "
        "    WHERE datname = 'template0';\n",

        /*
         * We use the OID of template0 to determine lastsysoid
         */
        "UPDATE pg_database SET datlastsysoid = "
        "    (SELECT oid FROM pg_database "
        "    WHERE datname = 'template0');\n",

        /*
         * Explicitly revoke public create-schema and create-temp-table
         * privileges in template1 and template0; else the latter would be on
         * by default
         */
        "REVOKE CREATE,TEMPORARY ON DATABASE template1 FROM public;\n",
        "REVOKE CREATE,TEMPORARY ON DATABASE template0 FROM public;\n",

        "COMMENT ON DATABASE template0 IS 'unmodifiable empty database';\n",

        /*
         * Finally vacuum to clean up dead rows in pg_database
         */
        "VACUUM FULL pg_database;\n",
        NULL
    };

    fputs(_("copying template1 to template0 ... "), stdout);
    fflush(stdout);

    snprintf(cmd, sizeof(cmd),
             "\"%s\" %s template1 >%s",
             backend_exec, backend_options,
             DEVNULL);

    PG_CMD_OPEN;

    for (line = template0_setup; *line; line++)
        PG_CMD_PUTS(*line);

    PG_CMD_CLOSE;

    check_ok();
}