本節繼續介紹排序的實現,上一節介紹了tuplesort_begin_heap/tuplesort_puttupleslot,本節介紹的函式是tuplesort_performsort.

### 一、資料結構
**TupleTableSlot**
執行器在"tuple table"中儲存元組,這個表是各自獨立的TupleTableSlots連結串列.
```
/*----------
 * The executor stores tuples in a "tuple table" which is a List of
 * independent TupleTableSlots.  There are several cases we need to handle:
 *      1. physical tuple in a disk buffer page
 *      2. physical tuple constructed in palloc'ed memory
 *      3. "minimal" physical tuple constructed in palloc'ed memory
 *      4. "virtual" tuple consisting of Datum/isnull arrays
 * 執行器在"tuple table"中儲存元組,這個表是各自獨立的TupleTableSlots連結串列.
 * 有以下情況需要處理:
 *      1. 磁碟快取頁中的物理元組
 *      2. 在已分配記憶體中構造的物理元組
 *      3. 在已分配記憶體中構造的"minimal"物理元組
 *      4. 含有Datum/isnull陣列的"virtual"虛擬元組
 *
 * The first two cases are similar in that they both deal with "materialized"
 * tuples, but resource management is different.  For a tuple in a disk page
 * we need to hold a pin on the buffer until the TupleTableSlot's reference
 * to the tuple is dropped; while for a palloc'd tuple we usually want the
 * tuple pfree'd when the TupleTableSlot's reference is dropped.
 * 最上面2種情況跟"物化"元組的處理方式類似,但資源管理是不同的.
 * 對於在磁碟頁中的元組,需要pin在快取中直至TupleTableSlot依賴的元組被清除,
 *   而對於透過palloc分配的元組在TupleTableSlot依賴被清除後通常希望使用pfree釋放
 *
 * A "minimal" tuple is handled similarly to a palloc'd regular tuple.
 * At present, minimal tuples never are stored in buffers, so there is no
 * parallel to case 1.  Note that a minimal tuple has no "system columns".
 * (Actually, it could have an OID, but we have no need to access the OID.)
 * "minimal"元組與通常的palloc分配的元組處理類似.
 * 截止目前為止,"minimal"元組不會儲存在快取中,因此對於第一種情況不會存在並行的問題.
 * 注意"minimal"沒有"system columns"系統列
 * (實際上,可以有OID,但不需要訪問OID列)
 *
 * A "virtual" tuple is an optimization used to minimize physical data
 * copying in a nest of plan nodes.  Any pass-by-reference Datums in the
 * tuple point to storage that is not directly associated with the
 * TupleTableSlot; generally they will point to part of a tuple stored in
 * a lower plan node's output TupleTableSlot, or to a function result
 * constructed in a plan node's per-tuple econtext.  It is the responsibility
 * of the generating plan node to be sure these resources are not released
 * for as long as the virtual tuple needs to be valid.  We only use virtual
 * tuples in the result slots of plan nodes --- tuples to be copied anywhere
 * else need to be "materialized" into physical tuples.  Note also that a
 * virtual tuple does not have any "system columns".
 * "virtual"元組是用於在巢狀計劃節點中複製時最小化物理資料的最佳化.
 * 所有透過引用傳遞指向與TupleTableSlot非直接相關的儲存的元組的Datums使用,
 *   通常它們會指向儲存在低層節點輸出的TupleTableSlot中的元組的一部分,
 *   或者指向在計劃節點的per-tuple記憶體上下文econtext中構造的函式結果.
 * 產生計劃節點的時候有責任確保這些資源未被釋放,確保virtual元組是有效的.
 * 我們使用計劃節點中的結果slots中的虛擬元組 --- 元組會複製到其他地方需要"物化"到物理元組中.
 * 注意virtual元組不需要有"system columns"
 *
 * It is also possible for a TupleTableSlot to hold both physical and minimal
 * copies of a tuple.  This is done when the slot is requested to provide
 * the format other than the one it currently holds.  (Originally we attempted
 * to handle such requests by replacing one format with the other, but that
 * had the fatal defect of invalidating any pass-by-reference Datums pointing
 * into the existing slot contents.)  Both copies must contain identical data
 * payloads when this is the case.
 * TupleTableSlot包含物理和minimal元組複製是可能的.
 * 在slot需要提供格式化而不是當前持有的格式時會出現這種情況.
 * (原始的情況是我們準備透過另外一種格式進行替換來處理這種請求,但在校驗引用傳遞Datums時會出現致命錯誤)
 * 同時在這種情況下,複製必須含有唯一的資料payloads.
 *
 * The Datum/isnull arrays of a TupleTableSlot serve double duty.  When the
 * slot contains a virtual tuple, they are the authoritative data.  When the
 * slot contains a physical tuple, the arrays contain data extracted from
 * the tuple.  (In this state, any pass-by-reference Datums point into
 * the physical tuple.)  The extracted information is built "lazily",
 * ie, only as needed.  This serves to avoid repeated extraction of data
 * from the physical tuple.
 * TupleTableSlot中的Datum/isnull陣列有雙重職責.
 * 在slot包含虛擬元組時,它們是authoritative(權威)資料.
 * 在slot包含物理元組時,時包含從元組中提取的資料的陣列.
 * (在這種情況下,所有透過引用傳遞的Datums指向物理元組)
 * 提取的資訊透過'lazily'在需要的時候才構建.
 * 這樣可以避免從物理元組的重複資料提取.
 *
 * A TupleTableSlot can also be "empty", holding no valid data.  This is
 * the only valid state for a freshly-created slot that has not yet had a
 * tuple descriptor assigned to it.  In this state, tts_isempty must be
 * true, tts_shouldFree false, tts_tuple NULL, tts_buffer InvalidBuffer,
 * and tts_nvalid zero.
 * TupleTableSlot可能為"empty",沒有有效資料.
 * 對於新鮮建立仍未分配描述的的slot來說這是唯一有效的狀態.
 * 在這種狀態下,tts_isempty必須為T,tts_shouldFree為F, tts_tuple為NULL,
 *   tts_buffer為InvalidBuffer,tts_nvalid為0.
 *
 * The tupleDescriptor is simply referenced, not copied, by the TupleTableSlot
 * code.  The caller of ExecSetSlotDescriptor() is responsible for providing
 * a descriptor that will live as long as the slot does.  (Typically, both
 * slots and descriptors are in per-query memory and are freed by memory
 * context deallocation at query end; so it's not worth providing any extra
 * mechanism to do more.  However, the slot will increment the tupdesc
 * reference count if a reference-counted tupdesc is supplied.)
 * tupleDescriptor只是簡單的引用並沒有透過TupleTableSlot中的程式碼進行複製.
 * ExecSetSlotDescriptor()的呼叫者有責任提供與slot生命週期一樣的描述符.
 * (典型的,不管是slots還是描述符會在per-query記憶體中,
 *  並且會在查詢結束時透過記憶體上下文的析構器釋放,因此不需要提供額外的機制來處理.
 *  但是,如果使用了引用計數型tupdesc,slot會增加tupdesc引用計數)
 *
 * When tts_shouldFree is true, the physical tuple is "owned" by the slot
 * and should be freed when the slot's reference to the tuple is dropped.
 * 在tts_shouldFree為T的情況下,物理元組由slot持有,並且在slot引用元組被清除時釋放記憶體.
 *
 * If tts_buffer is not InvalidBuffer, then the slot is holding a pin
 * on the indicated buffer page; drop the pin when we release the
 * slot's reference to that buffer.  (tts_shouldFree should always be
 * false in such a case, since presumably tts_tuple is pointing at the
 * buffer page.)
 * 如tts_buffer不是InvalidBuffer,那麼slot持有快取頁中的pin,在釋放引用該buffer的slot時會清除該pin.
 * (tts_shouldFree通常來說應為F,因為tts_tuple會指向快取頁)
 *
 * tts_nvalid indicates the number of valid columns in the tts_values/isnull
 * arrays.  When the slot is holding a "virtual" tuple this must be equal
 * to the descriptor's natts.  When the slot is holding a physical tuple
 * this is equal to the number of columns we have extracted (we always
 * extract columns from left to right, so there are no holes).
 * tts_nvalid指示了tts_values/isnull陣列中的有效列數.
 * 如果slot含有虛擬元組,該欄位必須跟描述符的natts一樣.
 * 在slot含有物理元組時,該欄位等於我們提取的列數.
 * (我們通常從左到右提取列,因此不會有空洞存在)
 *
 * tts_values/tts_isnull are allocated when a descriptor is assigned to the
 * slot; they are of length equal to the descriptor's natts.
 * 在描述符分配給slot時tts_values/tts_isnull會被分配記憶體,長度與描述符natts長度一樣.
 *
 * tts_mintuple must always be NULL if the slot does not hold a "minimal"
 * tuple.  When it does, tts_mintuple points to the actual MinimalTupleData
 * object (the thing to be pfree'd if tts_shouldFreeMin is true).  If the slot
 * has only a minimal and not also a regular physical tuple, then tts_tuple
 * points at tts_minhdr and the fields of that struct are set correctly
 * for access to the minimal tuple; in particular, tts_minhdr.t_data points
 * MINIMAL_TUPLE_OFFSET bytes before tts_mintuple.  This allows column
 * extraction to treat the case identically to regular physical tuples.
 * 如果slot沒有包含minimal元組,tts_mintuple通常必須為NULL.
 * 如含有,則tts_mintuple執行實際的MinimalTupleData物件(如tts_shouldFreeMin為T,則需要透過pfree釋放記憶體).
 * 如果slot只有一個minimal而沒有通常的物理元組,那麼tts_tuple指向tts_minhdr,
 *   結構體的其他欄位會被正確的設定為用於訪問minimal元組.
 *   特別的, tts_minhdr.t_data指向tts_mintuple前的MINIMAL_TUPLE_OFFSET位元組.
 * 這可以讓列提取可以獨立處理通常的物理元組.
 *
 * tts_slow/tts_off are saved state for slot_deform_tuple, and should not
 * be touched by any other code.
 * tts_slow/tts_off用於儲存slot_deform_tuple狀態,不應透過其他程式碼修改.
 *----------
 */
typedef struct TupleTableSlot
{
    NodeTag     type;//Node標記
    //如slot為空,則為T
    bool        tts_isempty;    /* true = slot is empty */
    //是否需要pfree tts_tuple?
    bool        tts_shouldFree; /* should pfree tts_tuple? */
    //是否需要pfree tts_mintuple?
    bool        tts_shouldFreeMin;  /* should pfree tts_mintuple? */
#define FIELDNO_TUPLETABLESLOT_SLOW 4
    //為slot_deform_tuple儲存狀態?
    bool        tts_slow;       /* saved state for slot_deform_tuple */
#define FIELDNO_TUPLETABLESLOT_TUPLE 5
    //物理元組,如為虛擬元組則為NULL
    HeapTuple   tts_tuple;      /* physical tuple, or NULL if virtual */
#define FIELDNO_TUPLETABLESLOT_TUPLEDESCRIPTOR 6
    //slot中的元組描述符
    TupleDesc   tts_tupleDescriptor;    /* slot's tuple descriptor */
    //slot所在的上下文
    MemoryContext tts_mcxt;     /* slot itself is in this context */
    //元組快取,如無則為InvalidBuffer
    Buffer      tts_buffer;     /* tuple's buffer, or InvalidBuffer */
#define FIELDNO_TUPLETABLESLOT_NVALID 9
    //tts_values中的有效值
    int         tts_nvalid;     /* # of valid values in tts_values */
#define FIELDNO_TUPLETABLESLOT_VALUES 10
    //當前每個屬性的值
    Datum      *tts_values;     /* current per-attribute values */
#define FIELDNO_TUPLETABLESLOT_ISNULL 11
    //isnull陣列
    bool       *tts_isnull;     /* current per-attribute isnull flags */
    //minimal元組,如無則為NULL
    MinimalTuple tts_mintuple;  /* minimal tuple, or NULL if none */
    //在minimal情況下的工作空間
    HeapTupleData tts_minhdr;   /* workspace for minimal-tuple-only case */
#define FIELDNO_TUPLETABLESLOT_OFF 14
    //slot_deform_tuple的儲存狀態
    uint32      tts_off;        /* saved state for slot_deform_tuple */
    //不能被變更的描述符(固定描述符)
    bool        tts_fixedTupleDescriptor;   /* descriptor can't be changed */
} TupleTableSlot;

/* base tuple table slot type */
typedef struct TupleTableSlot
{
    NodeTag     type;//Node標記
#define FIELDNO_TUPLETABLESLOT_FLAGS 1
    uint16      tts_flags;      /* 布林狀態;Boolean states */
#define FIELDNO_TUPLETABLESLOT_NVALID 2
    AttrNumber  tts_nvalid;     /* 在tts_values中有多少有效的values;# of valid values in tts_values */
    const TupleTableSlotOps *const tts_ops; /* slot的實際實現;implementation of slot */
#define FIELDNO_TUPLETABLESLOT_TUPLEDESCRIPTOR 4
    TupleDesc   tts_tupleDescriptor;    /* slot的元組描述符;slot's tuple descriptor */
#define FIELDNO_TUPLETABLESLOT_VALUES 5
    Datum      *tts_values;     /* 當前屬性值;current per-attribute values */
#define FIELDNO_TUPLETABLESLOT_ISNULL 6
    bool       *tts_isnull;     /* 當前屬性isnull標記;current per-attribute isnull flags */
    MemoryContext tts_mcxt;     /*記憶體上下文; slot itself is in this context */
} TupleTableSlot;

/* routines for a TupleTableSlot implementation */
//TupleTableSlot的"小程式"
struct TupleTableSlotOps
{
    /* Minimum size of the slot */
	//slot的最小化大小
    size_t          base_slot_size;

/* Initialization. */
    //初始化方法
    void (*init)(TupleTableSlot *slot);

/* Destruction. */
    //析構方法
    void (*release)(TupleTableSlot *slot);

/*
     * Clear the contents of the slot. Only the contents are expected to be
     * cleared and not the tuple descriptor. Typically an implementation of
     * this callback should free the memory allocated for the tuple contained
     * in the slot.
     * 清除slot中的內容。
     * 只希望清除內容，而不希望清除元組描述符。
     * 通常，這個回撥的實現應該釋放為slot中包含的元組分配的記憶體。
     */
    void (*clear)(TupleTableSlot *slot);

/*
     * Fill up first natts entries of tts_values and tts_isnull arrays with
     * values from the tuple contained in the slot. The function may be called
     * with natts more than the number of attributes available in the tuple,
     * in which case it should set tts_nvalid to the number of returned
     * columns.
     * 用slot中包含的元組的值填充tts_values和tts_isnull陣列的第一個natts條目。
     * 在呼叫該函式時，natts可能多於元組中可用屬性的數量，在這種情況下，
     *   應該將tts_nvalid設定為返回列的數量。
     */
    void (*getsomeattrs)(TupleTableSlot *slot, int natts);

/*
     * Returns value of the given system attribute as a datum and sets isnull
     * to false, if it's not NULL. Throws an error if the slot type does not
     * support system attributes.
     * 將給定系統屬性的值作為基準返回，如果不為NULL，
     *   則將isnull設定為false。如果slot型別不支援系統屬性，則引發錯誤。
     */
    Datum (*getsysattr)(TupleTableSlot *slot, int attnum, bool *isnull);

/*
     * Make the contents of the slot solely depend on the slot, and not on
     * underlying resources (like another memory context, buffers, etc).
     * 使slot的內容完全依賴於slot，而不是底層資源(如另一個記憶體上下文、緩衝區等)。
     */
    void (*materialize)(TupleTableSlot *slot);

/*
     * Copy the contents of the source slot into the destination slot's own
     * context. Invoked using callback of the destination slot.
     * 將源slot的內容複製到目標slot自己的上下文中。
     * 使用目標slot的回撥函式呼叫。
     */
    void (*copyslot) (TupleTableSlot *dstslot, TupleTableSlot *srcslot);

/*
     * Return a heap tuple "owned" by the slot. It is slot's responsibility to
     * free the memory consumed by the heap tuple. If the slot can not "own" a
     * heap tuple, it should not implement this callback and should set it as
     * NULL.
     * 返回slot“擁有”的堆元組。
     * slot負責釋放堆元組分配的記憶體。
     * 如果slot不能“擁有”堆元組，它不應該實現這個回撥函式，應該將它設定為NULL。
     */
    HeapTuple (*get_heap_tuple)(TupleTableSlot *slot);

/*
     * Return a minimal tuple "owned" by the slot. It is slot's responsibility
     * to free the memory consumed by the minimal tuple. If the slot can not
     * "own" a minimal tuple, it should not implement this callback and should
     * set it as NULL.
     * 返回slot“擁有”的最小元組。
     * slot負責釋放最小元組分配的記憶體。
     * 如果slot不能“擁有”最小元組，它不應該實現這個回撥函式，應該將它設定為NULL。
     */
    MinimalTuple (*get_minimal_tuple)(TupleTableSlot *slot);

/*
     * Return a copy of heap tuple representing the contents of the slot. The
     * copy needs to be palloc'd in the current memory context. The slot
     * itself is expected to remain unaffected. It is *not* expected to have
     * meaningful "system columns" in the copy. The copy is not be "owned" by
     * the slot i.e. the caller has to take responsibilty to free memory
     * consumed by the slot.
     * 返回表示slot內容的堆元組副本。
     * 需要在當前記憶體上下文中對副本進行記憶體分配palloc。
     * 預計slot本身不會受到影響。
     * 它不希望在副本中有有意義的“系統列”。副本不是slot“擁有”的，即呼叫方必須負責釋放slot消耗的記憶體。
     */
    HeapTuple (*copy_heap_tuple)(TupleTableSlot *slot);

/*
     * Return a copy of minimal tuple representing the contents of the slot. The
     * copy needs to be palloc'd in the current memory context. The slot
     * itself is expected to remain unaffected. It is *not* expected to have
     * meaningful "system columns" in the copy. The copy is not be "owned" by
     * the slot i.e. the caller has to take responsibilty to free memory
     * consumed by the slot.
     * 返回表示slot內容的最小元組的副本。
     * 需要在當前記憶體上下文中對副本進行palloc。
     * 預計slot本身不會受到影響。
     * 它不希望在副本中有有意義的“系統列”。副本不是slot“擁有”的，即呼叫方必須負責釋放slot消耗的記憶體。
     */
    MinimalTuple (*copy_minimal_tuple)(TupleTableSlot *slot);
};

typedef struct tupleDesc
{
    int         natts;          /* tuple中的屬性數量;number of attributes in the tuple */
    Oid         tdtypeid;       /* tuple型別的組合型別ID;composite type ID for tuple type */
    int32       tdtypmod;       /* tuple型別的typmode;typmod for tuple type */
    int         tdrefcount;     /* 依賴計數,如為-1,則沒有依賴;reference count, or -1 if not counting */
    TupleConstr *constr;        /* 約束,如無則為NULL;constraints, or NULL if none */
    /* attrs[N] is the description of Attribute Number N+1 */
	//attrs[N]是第N+1個屬性的描述符
    FormData_pg_attribute attrs[FLEXIBLE_ARRAY_MEMBER];
}  *TupleDesc;

```

**SortState**
排序執行期狀態資訊
```

/* ----------------
 *	 SortState information
 *	 排序執行期狀態資訊
 * ----------------
 */
typedef struct SortState
{
	//基類
	ScanState	ss;				/* its first field is NodeTag */
	//是否需要隨機訪問排序輸出?
	bool		randomAccess;	/* need random access to sort output? */
	//結果集是否存在邊界?
	bool		bounded;		/* is the result set bounded? */
	//如存在邊界,需要多少個元組?
	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的私有狀態
	void	   *tuplesortstate; /* private state of tuplesort.c */
	//是否worker?
	bool		am_worker;		/* are we a worker? */
	//每個worker對應一個條目
	SharedSortInfo *shared_info;	/* one entry per worker */
} SortState;

/* ----------------
 *	 Shared memory container for per-worker sort information
 *	 per-worker排序資訊的共享記憶體容器
 * ----------------
 */
typedef struct SharedSortInfo
{
	//worker個數?
	int			num_workers;
	//排序機制
	TuplesortInstrumentation sinstrument[FLEXIBLE_ARRAY_MEMBER];
} SharedSortInfo;

```

**TuplesortInstrumentation**
報告排序統計的資料結構.
```
/*
 * Data structures for reporting sort statistics.  Note that
 * TuplesortInstrumentation can't contain any pointers because we
 * sometimes put it in shared memory.
 * 報告排序統計的資料結構.
 * 注意TuplesortInstrumentation不能包含指標因為有時候會把該結構體放在共享記憶體中.
 */
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//外部排序後的合併
} TuplesortMethod;//排序方法

typedef enum
{
	SORT_SPACE_TYPE_DISK,//需要用上磁碟
	SORT_SPACE_TYPE_MEMORY//使用記憶體
} TuplesortSpaceType;

typedef struct TuplesortInstrumentation
{
	//使用的排序演算法
	TuplesortMethod sortMethod; /* sort algorithm used */
	//排序使用空間型別
	TuplesortSpaceType spaceType;	/* type of space spaceUsed represents */
	//空間消耗(以K為單位)
	long		spaceUsed;		/* space consumption, in kB */
} TuplesortInstrumentation;

```

### 二、原始碼解讀
tuplesort_performsort是排序的實現.

```

/*
 * All tuples have been provided; finish the sort.
 * 已存在元組,執行排序!
 */
void
tuplesort_performsort(Tuplesortstate *state)
{
	MemoryContext oldcontext = MemoryContextSwitchTo(state->sortcontext);

#ifdef TRACE_SORT
	if (trace_sort)
		elog(LOG, "performsort of worker %d starting: %s",
			 state->worker, pg_rusage_show(&state->ru_start));
#endif
	//根據狀態執行不同的邏輯
	switch (state->status)
	{
		case TSS_INITIAL:

/*
			 * We were able to accumulate all the tuples within the allowed
			 * amount of memory, or leader to take over worker tapes
			 * 可以在允許的記憶體大小中積累所有的元組,或者讓協調者接管工作tapes.
			 */
			if (SERIAL(state))
			{
				/* Just qsort 'em and we're done */
				//快速排序
				tuplesort_sort_memtuples(state);
				state->status = TSS_SORTEDINMEM;
			}
			else if (WORKER(state))
			{
				/*
				 * Parallel workers must still dump out tuples to tape.  No
				 * merge is required to produce single output run, though.
				 * 並行worker必須dump元組到磁碟上.
				 * 但是,生成單個輸出執行不需要合併.
				 */
				inittapes(state, false);
				dumptuples(state, true);
				worker_nomergeruns(state);
				state->status = TSS_SORTEDONTAPE;
			}
			else
			{
				/*
				 * Leader will take over worker tapes and merge worker runs.
				 * Note that mergeruns sets the correct state->status.
				 * 並行協調器會接管工作程式的資料併合並工作執行緒執行.
				 * 注意mergeruns會設定正確的狀態:state->status
				 */
				leader_takeover_tapes(state);
				mergeruns(state);
			}
			state->current = 0;
			state->eof_reached = false;
			state->markpos_block = 0L;
			state->markpos_offset = 0;
			state->markpos_eof = false;
			break;

case TSS_BOUNDED://堆排序

/*
			 * We were able to accumulate all the tuples required for output
			 * in memory, using a heap to eliminate excess tuples.  Now we
			 * have to transform the heap to a properly-sorted array.
			 * 使用堆來消除多餘的元組,在記憶體可以積累所有的元組用於輸出.
			 * 現在我們必須轉換堆為已排序的陣列.
			 */
			sort_bounded_heap(state);
			state->current = 0;
			state->eof_reached = false;
			state->markpos_offset = 0;
			state->markpos_eof = false;
			state->status = TSS_SORTEDINMEM;
			break;

case TSS_BUILDRUNS:

/*
			 * Finish tape-based sort.  First, flush all tuples remaining in
			 * memory out to tape; then merge until we have a single remaining
			 * run (or, if !randomAccess and !WORKER(), one run per tape).
			 * Note that mergeruns sets the correct state->status.
			 * 完成tape-based排序.
			 * 首先重新整理所有在記憶體的元組到tape(持久化儲存)上,然後合併直至只留下一個在執行.
			 * (否則,如果!randomAccess 且 !WORKER(),一個tape執行一次)
			 */
			//全部刷到磁碟上
			dumptuples(state, true);
			//合併執行
			mergeruns(state);
			state->eof_reached = false;
			state->markpos_block = 0L;
			state->markpos_offset = 0;
			state->markpos_eof = false;
			break;

default:
			elog(ERROR, "invalid tuplesort state");
			break;
	}

#ifdef TRACE_SORT
	if (trace_sort)
	{
		if (state->status == TSS_FINALMERGE)
			elog(LOG, "performsort of worker %d done (except %d-way final merge): %s",
				 state->worker, state->activeTapes,
				 pg_rusage_show(&state->ru_start));
		else
			elog(LOG, "performsort of worker %d done: %s",
				 state->worker, pg_rusage_show(&state->ru_start));
	}
#endif

MemoryContextSwitchTo(oldcontext);
}

```

### 三、跟蹤分析
測試指令碼
```
select * from t_sort order by c1,c2;

```
跟蹤分析
```
(gdb) b tuplesort_begin_heap
Breakpoint 1 at 0xa6ffa1: file tuplesort.c, line 812.
(gdb) b tuplesort_puttupleslot
Breakpoint 2 at 0xa7119d: file tuplesort.c, line 1436.
(gdb) b tuplesort_performsort
Breakpoint 3 at 0xa71f45: file tuplesort.c, line 1792.
(gdb) c
Continuing.

Breakpoint 1, tuplesort_begin_heap (tupDesc=0x208fa40, nkeys=2, attNums=0x2081858, sortOperators=0x2081878, 
    sortCollations=0x2081898, nullsFirstFlags=0x20818b8, workMem=4096, coordinate=0x0, randomAccess=false)
    at tuplesort.c:812
812		Tuplesortstate *state = tuplesort_begin_common(workMem, coordinate,
(gdb) 
```
**tuplesort_begin_heap**
輸入引數
```
(gdb) p *tupDesc
$1 = {natts = 7, tdtypeid = 2249, tdtypmod = -1, tdhasoid = false, tdrefcount = -1, constr = 0x0, attrs = 0x208fa60}
(gdb) p *tupDesc->attrs
$2 = {attrelid = 0, attname = {data = '\000' <repeats times="">}, atttypid = 1043, attstattarget = -1, attlen = -1, 
  attnum = 1, attndims = 0, attcacheoff = -1, atttypmod = 24, attbyval = false, attstorage = 120 'x', attalign = 105 'i', 
  attnotnull = false, atthasdef = false, atthasmissing = false, attidentity = 0 '\000', attisdropped = false, 
  attislocal = true, attinhcount = 0, attcollation = 100}
(gdb) p *attNums
$3 = 2
(gdb) p *sortOperators
$4 = 97
(gdb) p *sortCollations
$5 = 0
(gdb) p nullsFirstFlags
$6 = (_Bool *) 0x20818b8
(gdb) p *nullsFirstFlags
$7 = false
(gdb) 
```
獲取排序狀態,status = TSS_INITIAL
```
(gdb) p *state
$8 = {status = TSS_INITIAL, nKeys = 0, randomAccess = false, bounded = false, boundUsed = false, bound = 0, tuples = true, 
  availMem = 4169704, allowedMem = 4194304, maxTapes = 0, tapeRange = 0, sortcontext = 0x2093290, tuplecontext = 0x20992c0, 
  tapeset = 0x0, comparetup = 0x0, copytup = 0x0, writetup = 0x0, readtup = 0x0, memtuples = 0x209b310, memtupcount = 0, 
  memtupsize = 1024, growmemtuples = true, slabAllocatorUsed = false, slabMemoryBegin = 0x0, slabMemoryEnd = 0x0, 
  slabFreeHead = 0x0, read_buffer_size = 0, lastReturnedTuple = 0x0, currentRun = 0, mergeactive = 0x0, Level = 0, 
  destTape = 0, tp_fib = 0x0, tp_runs = 0x0, tp_dummy = 0x0, tp_tapenum = 0x0, activeTapes = 0, result_tape = -1, 
  current = 0, eof_reached = false, markpos_block = 0, markpos_offset = 0, markpos_eof = false, worker = -1, shared = 0x0, 
  nParticipants = -1, tupDesc = 0x0, sortKeys = 0x0, onlyKey = 0x0, abbrevNext = 0, indexInfo = 0x0, estate = 0x0, 
  heapRel = 0x0, indexRel = 0x0, enforceUnique = false, high_mask = 0, low_mask = 0, max_buckets = 0, datumType = 0, 
  datumTypeLen = 0, ru_start = {tv = {tv_sec = 0, tv_usec = 0}, ru = {ru_utime = {tv_sec = 0, tv_usec = 0}, ru_stime = {
        tv_sec = 0, tv_usec = 0}, {ru_maxrss = 0, __ru_maxrss_word = 0}, {ru_ixrss = 0, __ru_ixrss_word = 0}, {
        ru_idrss = 0, __ru_idrss_word = 0}, {ru_isrss = 0, __ru_isrss_word = 0}, {ru_minflt = 0, __ru_minflt_word = 0}, {
        ru_majflt = 0, __ru_majflt_word = 0}, {ru_nswap = 0, __ru_nswap_word = 0}, {ru_inblock = 0, __ru_inblock_word = 0}, 
      {ru_oublock = 0, __ru_oublock_word = 0}, {ru_msgsnd = 0, __ru_msgsnd_word = 0}, {ru_msgrcv = 0, 
        __ru_msgrcv_word = 0}, {ru_nsignals = 0, __ru_nsignals_word = 0}, {ru_nvcsw = 0, __ru_nvcsw_word = 0}, {
        ru_nivcsw = 0, __ru_nivcsw_word = 0}}}}
```
設定執行狀態
```
(gdb) n
819		AssertArg(nkeys > 0);
(gdb) 
822		if (trace_sort)
(gdb) 
828		state->nKeys = nkeys;
(gdb) 
830		TRACE_POSTGRESQL_SORT_START(HEAP_SORT,
(gdb) 
837		state->comparetup = comparetup_heap;
(gdb) 
838		state->copytup = copytup_heap;
(gdb) 
839		state->writetup = writetup_heap;
(gdb) 
840		state->readtup = readtup_heap;
(gdb) 
842		state->tupDesc = tupDesc;	/* assume we need not copy tupDesc */
(gdb) 
843		state->abbrevNext = 10;
(gdb) 
846		state->sortKeys = (SortSupport) palloc0(nkeys * sizeof(SortSupportData));
(gdb) 
848		for (i = 0; i < nkeys; i++)
(gdb) p *state
$9 = {status = TSS_INITIAL, nKeys = 2, randomAccess = false, bounded = false, boundUsed = false, bound = 0, tuples = true, 
  availMem = 4169704, allowedMem = 4194304, maxTapes = 0, tapeRange = 0, sortcontext = 0x2093290, tuplecontext = 0x20992c0, 
  tapeset = 0x0, comparetup = 0xa7525b <comparetup_heap>, copytup = 0xa76247 <copytup_heap>, 
  writetup = 0xa76de1 <writetup_heap>, readtup = 0xa76ec6 <readtup_heap>, memtuples = 0x209b310, memtupcount = 0, 
  memtupsize = 1024, growmemtuples = true, slabAllocatorUsed = false, slabMemoryBegin = 0x0, slabMemoryEnd = 0x0, 
  slabFreeHead = 0x0, read_buffer_size = 0, lastReturnedTuple = 0x0, currentRun = 0, mergeactive = 0x0, Level = 0, 
  destTape = 0, tp_fib = 0x0, tp_runs = 0x0, tp_dummy = 0x0, tp_tapenum = 0x0, activeTapes = 0, result_tape = -1, 
  current = 0, eof_reached = false, markpos_block = 0, markpos_offset = 0, markpos_eof = false, worker = -1, shared = 0x0, 
  nParticipants = -1, tupDesc = 0x208fa40, sortKeys = 0x20937c0, onlyKey = 0x0, abbrevNext = 10, indexInfo = 0x0, 
  estate = 0x0, heapRel = 0x0, indexRel = 0x0, enforceUnique = false, high_mask = 0, low_mask = 0, max_buckets = 0, 
  datumType = 0, datumTypeLen = 0, ru_start = {tv = {tv_sec = 0, tv_usec = 0}, ru = {ru_utime = {tv_sec = 0, tv_usec = 0}, 
      ru_stime = {tv_sec = 0, tv_usec = 0}, {ru_maxrss = 0, __ru_maxrss_word = 0}, {ru_ixrss = 0, __ru_ixrss_word = 0}, {
        ru_idrss = 0, __ru_idrss_word = 0}, {ru_isrss = 0, __ru_isrss_word = 0}, {ru_minflt = 0, __ru_minflt_word = 0}, {
        ru_majflt = 0, __ru_majflt_word = 0}, {ru_nswap = 0, __ru_nswap_word = 0}, {ru_inblock = 0, __ru_inblock_word = 0}, 
      {ru_oublock = 0, __ru_oublock_word = 0}, {ru_msgsnd = 0, __ru_msgsnd_word = 0}, {ru_msgrcv = 0, 
        __ru_msgrcv_word = 0}, {ru_nsignals = 0, __ru_nsignals_word = 0}, {ru_nvcsw = 0, __ru_nvcsw_word = 0}, {
        ru_nivcsw = 0, __ru_nivcsw_word = 0}}}}
(gdb) 
```
為每一列(c1&c2)準備SortSupport資料(分配記憶體空間)
```
(gdb) n
850			SortSupport sortKey = state->sortKeys + i;
(gdb) 
852			AssertArg(attNums[i] != 0);
(gdb) p *state->sortKeys
$10 = {ssup_cxt = 0x0, ssup_collation = 0, ssup_reverse = false, ssup_nulls_first = false, ssup_attno = 0, 
  ssup_extra = 0x0, comparator = 0x0, abbreviate = false, abbrev_converter = 0x0, abbrev_abort = 0x0, 
  abbrev_full_comparator = 0x0}
(gdb) n
853			AssertArg(sortOperators[i] != 0);
(gdb) 
855			sortKey->ssup_cxt = CurrentMemoryContext;
(gdb) 
856			sortKey->ssup_collation = sortCollations[i];
(gdb) 
857			sortKey->ssup_nulls_first = nullsFirstFlags[i];
(gdb) 
858			sortKey->ssup_attno = attNums[i];
(gdb) 
860			sortKey->abbreviate = (i == 0);
(gdb) 
862			PrepareSortSupportFromOrderingOp(sortOperators[i], sortKey);
(gdb) 
848		for (i = 0; i < nkeys; i++)
(gdb) 
850			SortSupport sortKey = state->sortKeys + i;
(gdb) 
852			AssertArg(attNums[i] != 0);
(gdb) 
853			AssertArg(sortOperators[i] != 0);
(gdb) 
855			sortKey->ssup_cxt = CurrentMemoryContext;
(gdb) 
856			sortKey->ssup_collation = sortCollations[i];
(gdb) 
857			sortKey->ssup_nulls_first = nullsFirstFlags[i];
(gdb) 
858			sortKey->ssup_attno = attNums[i];
(gdb) 
860			sortKey->abbreviate = (i == 0);
(gdb) 
862			PrepareSortSupportFromOrderingOp(sortOperators[i], sortKey);
(gdb) 
848		for (i = 0; i < nkeys; i++)
(gdb) 
```
完成初始化,返回state
```
(gdb) 
871		if (nkeys == 1 && !state->sortKeys->abbrev_converter)
(gdb) n
874		MemoryContextSwitchTo(oldcontext);
(gdb) 
876		return state;
(gdb) p *state
$11 = {status = TSS_INITIAL, nKeys = 2, randomAccess = false, bounded = false, boundUsed = false, bound = 0, tuples = true, 
  availMem = 4169704, allowedMem = 4194304, maxTapes = 0, tapeRange = 0, sortcontext = 0x2093290, tuplecontext = 0x20992c0, 
  tapeset = 0x0, comparetup = 0xa7525b <comparetup_heap>, copytup = 0xa76247 <copytup_heap>, 
  writetup = 0xa76de1 <writetup_heap>, readtup = 0xa76ec6 <readtup_heap>, memtuples = 0x209b310, memtupcount = 0, 
  memtupsize = 1024, growmemtuples = true, slabAllocatorUsed = false, slabMemoryBegin = 0x0, slabMemoryEnd = 0x0, 
  slabFreeHead = 0x0, read_buffer_size = 0, lastReturnedTuple = 0x0, currentRun = 0, mergeactive = 0x0, Level = 0, 
  destTape = 0, tp_fib = 0x0, tp_runs = 0x0, tp_dummy = 0x0, tp_tapenum = 0x0, activeTapes = 0, result_tape = -1, 
  current = 0, eof_reached = false, markpos_block = 0, markpos_offset = 0, markpos_eof = false, worker = -1, shared = 0x0, 
  nParticipants = -1, tupDesc = 0x208fa40, sortKeys = 0x20937c0, onlyKey = 0x0, abbrevNext = 10, indexInfo = 0x0, 
  estate = 0x0, heapRel = 0x0, indexRel = 0x0, enforceUnique = false, high_mask = 0, low_mask = 0, max_buckets = 0, 
  datumType = 0, datumTypeLen = 0, ru_start = {tv = {tv_sec = 0, tv_usec = 0}, ru = {ru_utime = {tv_sec = 0, tv_usec = 0}, 
      ru_stime = {tv_sec = 0, tv_usec = 0}, {ru_maxrss = 0, __ru_maxrss_word = 0}, {ru_ixrss = 0, __ru_ixrss_word = 0}, {
        ru_idrss = 0, __ru_idrss_word = 0}, {ru_isrss = 0, __ru_isrss_word = 0}, {ru_minflt = 0, __ru_minflt_word = 0}, {
        ru_majflt = 0, __ru_majflt_word = 0}, {ru_nswap = 0, __ru_nswap_word = 0}, {ru_inblock = 0, __ru_inblock_word = 0}, 
      {ru_oublock = 0, __ru_oublock_word = 0}, {ru_msgsnd = 0, __ru_msgsnd_word = 0}, {ru_msgrcv = 0, 
        __ru_msgrcv_word = 0}, {ru_nsignals = 0, __ru_nsignals_word = 0}, {ru_nvcsw = 0, __ru_nvcsw_word = 0}, {
        ru_nivcsw = 0, __ru_nivcsw_word = 0}}}}
(gdb) 
```

**tuplesort_puttupleslot**
出現在迴圈中
```
		for (;;)
		{
			//從outer plan中獲取元組
			slot = ExecProcNode(outerNode);

if (TupIsNull(slot))
				break;//直至全部獲取完畢
			//排序
			tuplesort_puttupleslot(tuplesortstate, slot);
		}

```
以其中一個slot為例說明
```
(gdb) c
Continuing.

Breakpoint 2, tuplesort_puttupleslot (state=0x20933a8, slot=0x208f8c8) at tuplesort.c:1436
1436		MemoryContext oldcontext = MemoryContextSwitchTo(state->sortcontext);
```
輸入引數,state為先前呼叫begin_heap返回的state,slot為outer node返回的元組slot
```
(gdb) p *slot
$12 = {type = T_TupleTableSlot, tts_isempty = false, tts_shouldFree = false, tts_shouldFreeMin = false, tts_slow = false, 
  tts_tuple = 0x2090678, tts_tupleDescriptor = 0x7f061a300380, tts_mcxt = 0x208f270, tts_buffer = 103, tts_nvalid = 0, 
  tts_values = 0x208f928, tts_isnull = 0x208f960, tts_mintuple = 0x0, tts_minhdr = {t_len = 0, t_self = {ip_blkid = {
        bi_hi = 0, bi_lo = 0}, ip_posid = 0}, t_tableOid = 0, t_data = 0x0}, tts_off = 0, tts_fixedTupleDescriptor = true}
(gdb) 
```
slot中的元組資料
```
(gdb) p *slot->tts_values
$13 = 0
(gdb) p *slot->tts_tuple
$14 = {t_len = 56, t_self = {ip_blkid = {bi_hi = 0, bi_lo = 0}, ip_posid = 1}, t_tableOid = 286759, t_data = 0x7f05ee0c4648}
(gdb) p *slot->tts_tuple->t_data
$15 = {t_choice = {t_heap = {t_xmin = 839, t_xmax = 0, t_field3 = {t_cid = 0, t_xvac = 0}}, t_datum = {datum_len_ = 839, 
      datum_typmod = 0, datum_typeid = 0}}, t_ctid = {ip_blkid = {bi_hi = 0, bi_lo = 0}, ip_posid = 1}, t_infomask2 = 7, 
  t_infomask = 2306, t_hoff = 24 '\030', t_bits = 0x7f05ee0c465f ""}
(gdb) p *slot->tts_tuple->t_data->t_bits
$16 = 0 '\000'
(gdb) x/16ux *slot->tts_tuple->t_data->t_bits
0x0:	Cannot access memory at address 0x0
(gdb) x/16ux slot->tts_tuple->t_data->t_bits
0x7f05ee0c465f:	0x5a470b00	0x00003130	0x00000100	0x00000100
0x7f05ee0c466f:	0x00000100	0x00000100	0x00000100	0x00000100
0x7f05ee0c467f:	0x00000000	0x8f282800	0x000000da	0x40023800
0x7f05ee0c468f:	0x04200002	0x00000020	0x709fc800	0x709f9000
(gdb) x/16bx slot->tts_tuple->t_data->t_bits
0x7f05ee0c465f:	0x00	0x0b	0x47	0x5a	0x30	0x31	0x00	0x00
0x7f05ee0c4667:	0x00	0x01	0x00	0x00	0x00	0x01	0x00	0x00
(gdb) x/16bc slot->tts_tuple->t_data->t_bits
0x7f05ee0c465f:	0 '\000'	11 '\v'	71 'G'	90 'Z'	48 '0'	49 '1'	0 '\000'	0 '\000'
0x7f05ee0c4667:	0 '\000'	1 '\001'	0 '\000'	0 '\000'	0 '\000'	1 '\001'	0 '\000'    0 '\000'
(gdb) p *slot->tts_tupleDescriptor
$17 = {natts = 7, tdtypeid = 286761, tdtypmod = -1, tdhasoid = false, tdrefcount = 2, constr = 0x0, attrs = 0x7f061a3003a0}
(gdb) p *slot
$18 = {type = T_TupleTableSlot, tts_isempty = false, tts_shouldFree = false, tts_shouldFreeMin = false, tts_slow = false, 
  tts_tuple = 0x2090678, tts_tupleDescriptor = 0x7f061a300380, tts_mcxt = 0x208f270, tts_buffer = 103, tts_nvalid = 0, 
  tts_values = 0x208f928, tts_isnull = 0x208f960, tts_mintuple = 0x0, tts_minhdr = {t_len = 0, t_self = {ip_blkid = {
        bi_hi = 0, bi_lo = 0}, ip_posid = 0}, t_tableOid = 0, t_data = 0x0}, tts_off = 0, tts_fixedTupleDescriptor = true}
(gdb) p *slot->tts_values[0]
Cannot access memory at address 0x0
(gdb) p slot->tts_values[0]
$19 = 0
(gdb) x/32bc slot->tts_tuple->t_data->t_bits
0x7f05ee0c465f:	0 '\000'	11 '\v'	71 'G'	90 'Z'	48 '0'	49 '1'	0 '\000'	0 '\000'
0x7f05ee0c4667:	0 '\000'	1 '\001'	0 '\000'	0 '\000'	0 '\000'	1 '\001'	0 '\000'    0 '\000'
0x7f05ee0c466f:	0 '\000'	1 '\001'	0 '\000'	0 '\000'	0 '\000'	1 '\001'	0 '\000'    0 '\000'
0x7f05ee0c4677:	0 '\000'	1 '\001'	0 '\000'	0 '\000'	0 '\000'	1 '\001'	0 '\000'    0 '\000'
(gdb) x/32bx slot->tts_tuple->t_data->t_bits
0x7f05ee0c465f:	0x00	0x0b	0x47	0x5a	0x30	0x31	0x00	0x00
0x7f05ee0c4667:	0x00	0x01	0x00	0x00	0x00	0x01	0x00	0x00
0x7f05ee0c466f:	0x00	0x01	0x00	0x00	0x00	0x01	0x00	0x00
0x7f05ee0c4677:	0x00	0x01	0x00	0x00	0x00	0x01	0x00	0x00
```
複製元組,並放到state->memtuples中
```
(gdb) n
1443		COPYTUP(state, &stup, (void *) slot);
(gdb) 
1445		puttuple_common(state, &stup);
(gdb) step
puttuple_common (state=0x20933a8, tuple=0x7ffe890e0b00) at tuplesort.c:1639
1639		Assert(!LEADER(state));
(gdb) n
1641		switch (state->status)
(gdb) p state->status
$20 = TSS_INITIAL
(gdb) n
1652				if (state->memtupcount >= state->memtupsize - 1)
(gdb) p state->memtupcount
$21 = 0
(gdb) p state->memtupsize - 1
$22 = 1023
(gdb) n
1657				state->memtuples[state->memtupcount++] = *tuple;
(gdb) 
1671				if (state->bounded &&
(gdb) p state->bounded
$23 = false
(gdb) n
1688				if (state->memtupcount < state->memtupsize && !LACKMEM(state))
(gdb) 
1689					return;
(gdb) 
1743	}
(gdb) 
tuplesort_puttupleslot (state=0x20933a8, slot=0x208f8c8) at tuplesort.c:1447
1447		MemoryContextSwitchTo(oldcontext);
(gdb) 
1448	}
(gdb) 
(gdb) p state->memtuples[0]
$25 = {tuple = 0x20993d8, datum1 = 1, isnull1 = false, tupindex = 0}
```
**tuplesort_performsort**

```
(gdb) info b
Num     Type           Disp Enb Address            What
1       breakpoint     keep y   0x0000000000a6ffa1 in tuplesort_begin_heap at tuplesort.c:812
	breakpoint already hit 1 time
2       breakpoint     keep y   0x0000000000a7119d in tuplesort_puttupleslot at tuplesort.c:1436
	breakpoint already hit 1 time
3       breakpoint     keep y   0x0000000000a71f45 in tuplesort_performsort at tuplesort.c:1792
(gdb) del 2
(gdb) c
Continuing.

Breakpoint 3, tuplesort_performsort (state=0x20933a8) at tuplesort.c:1792
1792		MemoryContext oldcontext = MemoryContextSwitchTo(state->sortcontext);
(gdb) 
```
輸入引數
```
(gdb) p *state
$27 = {status = TSS_BUILDRUNS, nKeys = 2, randomAccess = false, bounded = false, boundUsed = false, bound = 0, 
  tuples = true, availMem = 824360, allowedMem = 4194304, maxTapes = 16, tapeRange = 15, sortcontext = 0x2093290, 
  tuplecontext = 0x20992c0, tapeset = 0x2093a00, comparetup = 0xa7525b <comparetup_heap>, 
  copytup = 0xa76247 <copytup_heap>, writetup = 0xa76de1 <writetup_heap>, readtup = 0xa76ec6 <readtup_heap>, 
  memtuples = 0x2611570, memtupcount = 26592, memtupsize = 37448, growmemtuples = false, slabAllocatorUsed = false, 
  slabMemoryBegin = 0x0, slabMemoryEnd = 0x0, slabFreeHead = 0x0, read_buffer_size = 0, lastReturnedTuple = 0x0, 
  currentRun = 2, mergeactive = 0x2093878, Level = 1, destTape = 2, tp_fib = 0x20938a0, tp_runs = 0x20938f8, 
  tp_dummy = 0x2093950, tp_tapenum = 0x20939a8, activeTapes = 0, result_tape = -1, current = 0, eof_reached = false, 
  markpos_block = 0, markpos_offset = 0, markpos_eof = false, worker = -1, shared = 0x0, nParticipants = -1, 
  tupDesc = 0x208fa40, sortKeys = 0x20937c0, onlyKey = 0x0, abbrevNext = 10, indexInfo = 0x0, estate = 0x0, heapRel = 0x0, 
  indexRel = 0x0, enforceUnique = false, high_mask = 0, low_mask = 0, max_buckets = 0, datumType = 0, datumTypeLen = 0, 
  ru_start = {tv = {tv_sec = 0, tv_usec = 0}, ru = {ru_utime = {tv_sec = 0, tv_usec = 0}, ru_stime = {tv_sec = 0, 
        tv_usec = 0}, {ru_maxrss = 0, __ru_maxrss_word = 0}, {ru_ixrss = 0, __ru_ixrss_word = 0}, {ru_idrss = 0, 
        __ru_idrss_word = 0}, {ru_isrss = 0, __ru_isrss_word = 0}, {ru_minflt = 0, __ru_minflt_word = 0}, {ru_majflt = 0, 
        __ru_majflt_word = 0}, {ru_nswap = 0, __ru_nswap_word = 0}, {ru_inblock = 0, __ru_inblock_word = 0}, {
        ru_oublock = 0, __ru_oublock_word = 0}, {ru_msgsnd = 0, __ru_msgsnd_word = 0}, {ru_msgrcv = 0, 
        __ru_msgrcv_word = 0}, {ru_nsignals = 0, __ru_nsignals_word = 0}, {ru_nvcsw = 0, __ru_nvcsw_word = 0}, {
        ru_nivcsw = 0, __ru_nivcsw_word = 0}}}}
(gdb) p state->memtupsize
$28 = 37448
(gdb) 
```
state->status狀態已切換為TSS_BUILDRUNS
```
(gdb) n
1795		if (trace_sort)
(gdb) 
1800		switch (state->status)
(gdb) p state->status
$29 = TSS_BUILDRUNS
(gdb) 
```
全部刷到磁碟上,歸併排序
```
(gdb) n
1864				dumptuples(state, true);
(gdb) 
1865				mergeruns(state);
(gdb) 
1866				state->eof_reached = false;
(gdb) 
1867				state->markpos_block = 0L;
(gdb) 
1868				state->markpos_offset = 0;
(gdb) 
1869				state->markpos_eof = false;
(gdb) 
1870				break;
(gdb) 
1878		if (trace_sort)
(gdb) 
1890		MemoryContextSwitchTo(oldcontext);
(gdb) 
1891	}
(gdb) 
```
DONE!

### 四、參考資料
N/A</readtup_heap></writetup_heap></copytup_heap></comparetup_heap></readtup_heap></writetup_heap></copytup_heap></comparetup_heap></readtup_heap></writetup_heap></copytup_heap></comparetup_heap></repeats>

PostgreSQL 原始碼解讀（195）- 查詢#111(排序#4 - 實現)

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