本节介绍排序的实现,排序的实现函数是ExecSort,与聚合函数类似,也有要一个初始化的过程ExecInitSort,本节主要介绍该函数的实现.

下面是测试SQL执行排序的计划树:
```
",,,,,"select bh,c1 from t_sort order by t_sort;",,,"psql"
2019-05-17 15:12:42.494 CST,"xdb","testdb",1519,"[local]",5cde5e9e.5ef,15,"SELECT",2019-05-17 15:11:26 CST,3/10,0,LOG,00000,"plan:","   {PLANNEDSTMT 
   :commandType 1 
   :queryId 0 
   :hasReturning false 
   :hasModifyingCTE false 
   :canSetTag true 
   :transientPlan false 
   :dependsOnRole false 
   :parallelModeNeeded false 
   :jitFlags 0 
   :planTree 
      {SORT 
      :startup_cost 14142.82 
      :total_cost 14392.82 
      :plan_rows 100000 
      :plan_width 66 
      :parallel_aware false 
      :parallel_safe true 
      :plan_node_id 0 
      :targetlist (...
      )
      :qual <> 
      :lefttree 
         {SEQSCAN 
         :startup_cost 0.00 
         :total_cost 1736.00 
         :plan_rows 100000 
         :plan_width 66 
         :parallel_aware false 
         :parallel_safe true 
         :plan_node_id 1 
         :targetlist (...
         )
         :qual <> 
         :lefttree <> 
         :righttree <> 
         :initPlan <> 
         :extParam (b)
         :allParam (b)
         :scanrelid 1
         }
      :righttree <> 
      :initPlan <> 
      :extParam (b)
      :allParam (b)
      :numCols 1 
      :sortColIdx 3 
      :sortOperators 2990 
      :collations 0 
      :nullsFirst false
      }
   :rtable (...
   )
   :resultRelations <> 
   :nonleafResultRelations <> 
   :rootResultRelations <> 
   :subplans <> 
   :rewindPlanIDs (b)
   :rowMarks <> 
   :relationOids (o 278567)
   :invalItems <> 
   :paramExecTypes <> 
   :utilityStmt <> 
   :stmt_location 0 
   :stmt_len 40
   }
",,,,,"select bh,c1 from t_sort order by t_sort;",,,"psql"

```

### 一、数据结构
**SortState**
排序运行期状态信息
```

/* ----------------
 *	 SortState information
 *	 排序运行期状态信息
 * ----------------
 */
typedef struct SortState
{
	//基类
	ScanState	ss;				/* its first field is NodeTag */
	//是否需要随机访问排序输出?
	bool		randomAccess;	/* need random access to sort output? */
	//结果集是否存在边界?
	bool		bounded;		/* is the result set bounded? */
	//如存在边界,需要多少个元组?
	int64		bound;			/* if bounded, how many tuples are needed */
	//是否已完成排序?
	bool		sort_Done;		/* sort completed yet? */
	//是否使用有界值?
	bool		bounded_Done;	/* value of bounded we did the sort with */
	//使用的有界值?
	int64		bound_Done;		/* value of bound we did the sort with */
	//tuplesort.c的私有状态
	void	   *tuplesortstate; /* private state of tuplesort.c */
	//是否worker?
	bool		am_worker;		/* are we a worker? */
	//每个worker对应一个条目
	SharedSortInfo *shared_info;	/* one entry per worker */
} SortState;

/* ----------------
 *	 Shared memory container for per-worker sort information
 *	 per-worker排序信息的共享内存容器
 * ----------------
 */
typedef struct SharedSortInfo
{
	//worker个数?
	int			num_workers;
	//排序机制
	TuplesortInstrumentation sinstrument[FLEXIBLE_ARRAY_MEMBER];
} SharedSortInfo;

```

**TuplesortInstrumentation**
报告排序统计的数据结构.
```
/*
 * Data structures for reporting sort statistics.  Note that
 * TuplesortInstrumentation can't contain any pointers because we
 * sometimes put it in shared memory.
 * 报告排序统计的数据结构.
 * 注意TuplesortInstrumentation不能包含指针因为有时候会把该结构体放在共享内存中.
 */
typedef enum
{
	SORT_TYPE_STILL_IN_PROGRESS = 0,//仍然在排序中
	SORT_TYPE_TOP_N_HEAPSORT,//TOP N 堆排序
	SORT_TYPE_QUICKSORT,//快速排序
	SORT_TYPE_EXTERNAL_SORT,//外部排序
	SORT_TYPE_EXTERNAL_MERGE//外部排序后的合并
} TuplesortMethod;//排序方法

typedef enum
{
	SORT_SPACE_TYPE_DISK,//需要用上磁盘
	SORT_SPACE_TYPE_MEMORY//使用内存
} TuplesortSpaceType;

typedef struct TuplesortInstrumentation
{
	//使用的排序算法
	TuplesortMethod sortMethod; /* sort algorithm used */
	//排序使用空间类型
	TuplesortSpaceType spaceType;	/* type of space spaceUsed represents */
	//空间消耗(以K为单位)
	long		spaceUsed;		/* space consumption, in kB */
} TuplesortInstrumentation;

```

### 二、源码解读
ExecInitSort为排序节点创建运行期信息并初始化outer子树,逻辑较为简单.
```

/* ----------------------------------------------------------------
 *		ExecInitSort
 *
 *		Creates the run-time state information for the sort node
 *		produced by the planner and initializes its outer subtree.
 * ----------------------------------------------------------------
 */
SortState *
ExecInitSort(Sort *node, EState *estate, int eflags)
{
	SortState  *sortstate;//排序运行期信息

SO1_printf("ExecInitSort: %s\n",
			   "initializing sort node");

/*
	 * create state structure
	 * 创建运行期状态节点结构体
	 */
	sortstate = makeNode(SortState);
	sortstate->ss.ps.plan = (Plan *) node;
	sortstate->ss.ps.state = estate;
	sortstate->ss.ps.ExecProcNode = ExecSort;

/*
	 * We must have random access to the sort output to do backward scan or
	 * mark/restore.  We also prefer to materialize the sort output if we
	 * might be called on to rewind and replay it many times.
	 * 需要随机访问用于排序输出用于执行后端搜索或者标记/存储.
	 * 同时,如果可能在rewind或replay很多次的情况下,会倾向于物化排序输出
	 */
	sortstate->randomAccess = (eflags & (EXEC_FLAG_REWIND |
										 EXEC_FLAG_BACKWARD |
										 EXEC_FLAG_MARK)) != 0;

sortstate->bounded = false;//结果集不存在边界
	sortstate->sort_Done = false;//未完成排序
	sortstate->tuplesortstate = NULL;//元组排序状态为NULL

/*
	 * Miscellaneous initialization
	 * 执行各种初始化
	 *
	 * Sort nodes don't initialize their ExprContexts because they never call
	 * ExecQual or ExecProject.
	 * 排序节点不需要初始化ExprContexts,因为排序不会调用ExecQual/ExecProject
	 */

/*
	 * initialize child nodes
	 * 初始化子节点
	 *
	 * We shield the child node from the need to support REWIND, BACKWARD, or
	 * MARK/RESTORE.
	 * 子节点不需要支持REWIND, BACKWARD, MARK/RESTORE
	 */
	eflags &= ~(EXEC_FLAG_REWIND | EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK);
	//外(左)子节点往往是扫描节点,如SeqScan等
	outerPlanState(sortstate) = ExecInitNode(outerPlan(node), estate, eflags);

/*
	 * Initialize scan slot and type.
	 * 初始化扫描slot和类型
	 */
	ExecCreateScanSlotFromOuterPlan(estate, &sortstate->ss);

/*
	 * Initialize return slot and type. No need to initialize projection info
	 * because this node doesn't do projections.
	 * 初始化返回slot和类型.
	 * 不需要初始化投影信息因为排序节点不需要投影.
	 */
	ExecInitResultTupleSlotTL(estate, &sortstate->ss.ps);
	sortstate->ss.ps.ps_ProjInfo = NULL;

SO1_printf("ExecInitSort: %s\n",
			   "sort node initialized");

return sortstate;
}

/* ----------------
 *		ExecCreateSlotFromOuterPlan
 * ----------------
 */
void
ExecCreateScanSlotFromOuterPlan(EState *estate, ScanState *scanstate)
{
	PlanState  *outerPlan;
	TupleDesc	tupDesc;

outerPlan = outerPlanState(scanstate);
	tupDesc = ExecGetResultType(outerPlan);

ExecInitScanTupleSlot(estate, scanstate, tupDesc);
}

/* ----------------
 *		ExecInitScanTupleSlot
 * ----------------
 */
void
ExecInitScanTupleSlot(EState *estate, ScanState *scanstate, TupleDesc tupledesc)
{
	scanstate->ss_ScanTupleSlot = ExecAllocTableSlot(&estate->es_tupleTable,
													 tupledesc);
	scanstate->ps.scandesc = tupledesc;
}

```

### 三、跟踪分析
N/A

### 四、参考资料
N/A

ITPub博客

PostgreSQL 源码解读（192）- 查询#108(排序#1 - ExecInitSort)

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