BootstrapModeMain函数不会运行SQL，但是可以运行特殊的bootstrap语言，也就是从bki解析出来的语句。

/*   The main entry point for running the backend in bootstrap mode
 *  The bootstrap mode is used to initialize the template database.
 *  The bootstrap backend doesn't speak SQL, but instead expects
 *  commands in a special bootstrap language. */
static void BootstrapModeMain(void) {
  int      i;
  /* To ensure that src/common/link-canary.c is linked into the backend, we must call it from somewhere.  Here is as good as anywhere. */
  if (pg_link_canary_is_frontend()) elog(ERROR, "backend is incorrectly linked to frontend functions");  
  /* Do backend-like initialization for bootstrap mode */
  InitProcess();
  InitPostgres(NULL, InvalidOid, NULL, InvalidOid, NULL, false);

  /* Initialize stuff for bootstrap-file processing */
  for (i = 0; i < MAXATTR; i++) {
    attrtypes[i] = NULL; Nulls[i] = false;
  }
  /* Process bootstrap input. */ // boot_yyparse解析bki特殊的bootstrap语言
  StartTransactionCommand();
  boot_yyparse();
  CommitTransactionCommand();

  /* We should now know about all mapped relations, so it's okay to write out the initial relation mapping files. */
  RelationMapFinishBootstrap();

  /* Clean up and exit */
  cleanup(); proc_exit(0);
}

PG主程序模块（Main）——BootstrapModeMain从bki解析语句_postgresql