PostgreSQL数据库查询——pg_rewrite_query对语句进行重写

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mb62de8abf75c00 2022-07-26 17:09:17 ©著作权

文章标签 postgresql 数据库 database #ifdef #endif 文章分类 运维

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src/backend/tcop/postgres.c

static List *pg_rewrite_query(Query *query) {
  List     *querytree_list;
  
  if (log_parser_stats) ResetUsage();
  if (query->commandType == CMD_UTILITY) {
    /* don't rewrite utilities, just dump 'em into result list */
    querytree_list = list_make1(query);
  } else {
    /* rewrite regular queries */
    querytree_list = QueryRewrite(query);
  }
  if (log_parser_stats) ShowUsage("REWRITER STATISTICS");

#ifdef COPY_PARSE_PLAN_TREES
  /* Optional debugging check: pass querytree through copyObject() */
  {
    List     *new_list;
    new_list = copyObject(querytree_list);
    /* This checks both copyObject() and the equal() routines... */
    if (!equal(new_list, querytree_list))
      elog(WARNING, "copyObject() failed to produce equal parse tree");
    else
      querytree_list = new_list;
  }
#endif
#ifdef WRITE_READ_PARSE_PLAN_TREES
  /* Optional debugging check: pass querytree through outfuncs/readfuncs */
  {
    List     *new_list = NIL;
    ListCell   *lc;
    /* We currently lack outfuncs/readfuncs support for most utility
     * statement types, so only attempt to write/read non-utility queries. */
    foreach(lc, querytree_list) {
      Query     *query = castNode(Query, lfirst(lc));
      if (query->commandType != CMD_UTILITY) {
        char     *str = nodeToString(query);
        Query     *new_query = stringToNodeWithLocations(str);
        /* queryId is not saved in stored rules, but we must preserve
         * it here to avoid breaking pg_stat_statements. */
        new_query->queryId = query->queryId;
        new_list = lappend(new_list, new_query);
        pfree(str);
      }
      else
        new_list = lappend(new_list, query);
    }
    /* This checks both outfuncs/readfuncs and the equal() routines... */
    if (!equal(new_list, querytree_list))
      elog(WARNING, "outfuncs/readfuncs failed to produce equal parse tree");
    else
      querytree_list = new_list;
  }
#endif

  return querytree_list;
}