本節介紹了PostgreSQL含有NOT IN查詢語句實現中的ExecMaterial函式.

### 一、資料結構
**SubPlanState**
子計劃執行期狀態
```

/* ----------------
 *		SubPlanState node
 * ----------------
 */
typedef struct SubPlanState
{
	NodeTag		type;
	SubPlan    *subplan;		/* expression plan node */
	struct PlanState *planstate;	/* subselect plan's state tree */
	struct PlanState *parent;	/* parent plan node's state tree */
	ExprState  *testexpr;		/* 組合表示式狀態；state of combining expression */
	List	   *args;			/* 參數列達式狀態；states of argument expression(s) */
	HeapTuple	curTuple;		/* subplan最近的元組；copy of most recent tuple from subplan */
	Datum		curArray;		/* most recent array from ARRAY() subplan */
	/* these are used when hashing the subselect's output: */
	TupleDesc	descRight;		/* 投影后的子查詢描述符；subselect desc after projection */
	ProjectionInfo *projLeft;	/* for projecting lefthand exprs */
	ProjectionInfo *projRight;	/* for projecting subselect output */
	TupleHashTable hashtable;	/* hash table for no-nulls subselect rows */
	TupleHashTable hashnulls;	/* hash table for rows with null(s) */
	bool		havehashrows;	/* true if hashtable is not empty */
	bool		havenullrows;	/* true if hashnulls is not empty */
	MemoryContext hashtablecxt; /* memory context containing hash tables */
	MemoryContext hashtempcxt;	/* temp memory context for hash tables */
	ExprContext *innerecontext; /* econtext for computing inner tuples */
	AttrNumber *keyColIdx;		/* control data for hash tables */
	Oid		   *tab_eq_funcoids;	/* equality func oids for table
									 * datatype(s) */
	Oid		   *tab_collations; /* collations for hash and comparison */
	FmgrInfo   *tab_hash_funcs; /* hash functions for table datatype(s) */
	FmgrInfo   *tab_eq_funcs;	/* equality functions for table datatype(s) */
	FmgrInfo   *lhs_hash_funcs; /* hash functions for lefthand datatype(s) */
	FmgrInfo   *cur_eq_funcs;	/* equality functions for LHS vs. table */
	ExprState  *cur_eq_comp;	/* equality comparator for LHS vs. table */
} SubPlanState;

```

**SubPlan**
子查詢計劃
```

/*
 * SubPlan - executable expression node for a subplan (sub-SELECT)
 *
 * The planner replaces SubLink nodes in expression trees with SubPlan
 * nodes after it has finished planning the subquery.  SubPlan references
 * a sub-plantree stored in the subplans list of the toplevel PlannedStmt.
 * (We avoid a direct link to make it easier to copy expression trees
 * without causing multiple processing of the subplan.)
 * 查詢規劃器在完成子查詢的規劃後使用SubPlan節點替換表示式樹中的SubLink節點。
 * SubPlan引用了儲存在高層PlannedStmt中的subplans連結串列中的sub-plantree。
 * （避免使用直接連結，從而使得複製表示式樹相對比較簡單）
 *
 * In an ordinary subplan, testexpr points to an executable expression
 * (OpExpr, an AND/OR tree of OpExprs, or RowCompareExpr) for the combining
 * operator(s); the left-hand arguments are the original lefthand expressions,
 * and the right-hand arguments are PARAM_EXEC Param nodes representing the
 * outputs of the sub-select.  (NOTE: runtime coercion functions may be
 * inserted as well.)  This is just the same expression tree as testexpr in
 * the original SubLink node, but the PARAM_SUBLINK nodes are replaced by
 * suitably numbered PARAM_EXEC nodes.
 * 常規情況下，testexpr指向用於組合操作的可執行表示式（OpExpr、OpExprs的AND/OR樹或者RowCompareExpr）；
 * 左引數是原始的左表示式，右引數是PARAM_EXEC引數節點用以表示子查詢的輸出。
 * 與原始SubLink節點的testexpr具有相同的表示式樹，但PARAM_SUBLINK節點則使用合適的已編號PARAM_EXEC節點替代。
 *
 * If the sub-select becomes an initplan rather than a subplan, the executable
 * expression is part of the outer plan's expression tree (and the SubPlan
 * node itself is not, but rather is found in the outer plan's initPlan
 * list).  In this case testexpr is NULL to avoid duplication.
 * 如果子查詢成了initplan而不是subplan，可執行的表示式是外層plan表示式樹的一部分。
 * 這種情況下，testexpr為NULL以避免重複。
 *
 * The planner also derives lists of the values that need to be passed into
 * and out of the subplan.  Input values are represented as a list "args" of
 * expressions to be evaluated in the outer-query context (currently these
 * args are always just Vars, but in principle they could be any expression).
 * The values are assigned to the global PARAM_EXEC params indexed by parParam
 * (the parParam and args lists must have the same ordering).  setParam is a
 * list of the PARAM_EXEC params that are computed by the sub-select, if it
 * is an initplan; they are listed in order by sub-select output column
 * position.  (parParam and setParam are integer Lists, not Bitmapsets,
 * because their ordering is significant.)
 * 規劃器還派生了需要傳入和傳出子計劃的值的連結串列。
 * 輸入值標識位表示式的“args”連結串列，在外層查詢上下文中進行解析。
 * （這些args通常是Vars，但原則上它們可以是任意表示式）
 * 這些值以parParam為索引給全域性PARAM_EXEC引數賦值。
 * setParam是PARAM_EXEC引數連結串列，透過子查詢（如為initplan）計算所得。
 * 它們按子查詢輸出列的位置進行排序組織為連結串列形式。
 * （parParam和setParam是整型連結串列，而不是Bitmapsets連結串列）
 *
 * Also, the planner computes startup and per-call costs for use of the
 * SubPlan.  Note that these include the cost of the subquery proper,
 * evaluation of the testexpr if any, and any hashtable management overhead.
 * 同時，規劃器計算SubPlan啟動和每次呼叫的成本。注意：包括子查詢正常解析testexpr的成本以及雜湊表管理成本。
 */
typedef struct SubPlan
{
	Expr		xpr;//表示式
	/* Fields copied from original SubLink: */
	//從SubLink中複製而來
	SubLinkType subLinkType;	/* see above */
	/* The combining operators, transformed to an executable expression: */
	//組合運算子,轉換為可執行的表示式
	Node	   *testexpr;		/* OpExpr or RowCompareExpr expression tree */
	List	   *paramIds;		/* 引數IDs;IDs of Params embedded in the above */
	/* Identification of the Plan tree to use: */
	//Plan tree標識
	int			plan_id;		/* Index (from 1) in PlannedStmt.subplans */
	/* Identification of the SubPlan for EXPLAIN and debugging purposes: */
	//EXPLAIN和debug目的的SubPlan標識
	char	   *plan_name;		/* A name assigned during planning */
	/* Extra data useful for determining subplan's output type: */
	//用於確定subplan輸出型別的額外資訊
	Oid			firstColType;	/* subplan結果的第一個列型別;Type of first column of subplan result */
	int32		firstColTypmod; /* 第一列的Typmod;Typmod of first column of subplan result */
	Oid			firstColCollation;	/* 第一列的Collation;Collation of first column of subplan
									 * result */
	/* Information about execution strategy: */
	//執行階段的相關資訊
	bool		useHashTable;	/* 是否使用雜湊表儲存子查詢輸出;true to store subselect output in a hash
								 * table (implies we are doing "IN") */
	bool		unknownEqFalse; /* 如OK為T,如為未知則為F;快速處理null值;true if it's okay to return FALSE when the
								 * spec result is UNKNOWN; this allows much
								 * simpler handling of null values */
	bool		parallel_safe;	/* 是否並行安全?is the subplan parallel-safe? */
	/* Note: parallel_safe does not consider contents of testexpr or args */
	/* Information for passing params into and out of the subselect: */
	//用於給子查詢傳入和傳出引數的資訊
	/* setParam and parParam are lists of integers (param IDs) */
	//setParam和parParam是整型連結串列(param IDs)
	List	   *setParam;		/* initplan subqueries have to set these
								 * Params for parent plan */
	List	   *parParam;		/* indices of input Params from parent plan */
	List	   *args;			/* 以parParam值進行傳遞的表示式；exprs to pass as parParam values */
	/* Estimated execution costs: */
	//估算執行成本
	Cost		startup_cost;	/* one-time setup cost */
	Cost		per_call_cost;	/* cost for each subplan evaluation */
} SubPlan;

```

**SubLinkType**
SubLink型別
```

/*
 * SubLink
 *
 * A SubLink represents a subselect appearing in an expression, and in some
 * cases also the combining operator(s) just above it.  The subLinkType
 * indicates the form of the expression represented:
 *	EXISTS_SUBLINK		EXISTS(SELECT ...)
 *	ALL_SUBLINK			(lefthand) op ALL (SELECT ...)
 *	ANY_SUBLINK			(lefthand) op ANY (SELECT ...)
 *	ROWCOMPARE_SUBLINK	(lefthand) op (SELECT ...)
 *	EXPR_SUBLINK		(SELECT with single targetlist item ...)
 *	MULTIEXPR_SUBLINK	(SELECT with multiple targetlist items ...)
 *	ARRAY_SUBLINK		ARRAY(SELECT with single targetlist item ...)
 *	CTE_SUBLINK			WITH query (never actually part of an expression)
 * For ALL, ANY, and ROWCOMPARE, the lefthand is a list of expressions of the
 * same length as the subselect's targetlist.  ROWCOMPARE will *always* have
 * a list with more than one entry; if the subselect has just one target
 * then the parser will create an EXPR_SUBLINK instead (and any operator
 * above the subselect will be represented separately).
 * ROWCOMPARE, EXPR, and MULTIEXPR require the subselect to deliver at most
 * one row (if it returns no rows, the result is NULL).
 * ALL, ANY, and ROWCOMPARE require the combining operators to deliver boolean
 * results.  ALL and ANY combine the per-row results using AND and OR
 * semantics respectively.
 * ARRAY requires just one target column, and creates an array of the target
 * column's type using any number of rows resulting from the subselect.
 *
 * SubLink is classed as an Expr node, but it is not actually executable;
 * it must be replaced in the expression tree by a SubPlan node during
 * planning.
 *
 * NOTE: in the raw output of gram.y, testexpr contains just the raw form
 * of the lefthand expression (if any), and operName is the String name of
 * the combining operator.  Also, subselect is a raw parsetree.  During parse
 * analysis, the parser transforms testexpr into a complete boolean expression
 * that compares the lefthand value(s) to PARAM_SUBLINK nodes representing the
 * output columns of the subselect.  And subselect is transformed to a Query.
 * This is the representation seen in saved rules and in the rewriter.
 *
 * In EXISTS, EXPR, MULTIEXPR, and ARRAY SubLinks, testexpr and operName
 * are unused and are always null.
 *
 * subLinkId is currently used only for MULTIEXPR SubLinks, and is zero in
 * other SubLinks.  This number identifies different multiple-assignment
 * subqueries within an UPDATE statement's SET list.  It is unique only
 * within a particular targetlist.  The output column(s) of the MULTIEXPR
 * are referenced by PARAM_MULTIEXPR Params appearing elsewhere in the tlist.
 *
 * The CTE_SUBLINK case never occurs in actual SubLink nodes, but it is used
 * in SubPlans generated for WITH subqueries.
 */
typedef enum SubLinkType
{
	EXISTS_SUBLINK,
	ALL_SUBLINK,
	ANY_SUBLINK,
	ROWCOMPARE_SUBLINK,
	EXPR_SUBLINK,
	MULTIEXPR_SUBLINK,
	ARRAY_SUBLINK,
	CTE_SUBLINK					/* for SubPlans only */
} SubLinkType;

```

**SubLink**
SubLink結構體
```

typedef struct SubLink
{
	Expr		xpr;
	SubLinkType subLinkType;	/* see above */
	int			subLinkId;		/* ID (1..n); 0 if not MULTIEXPR */
	Node	   *testexpr;		/* outer-query test for ALL/ANY/ROWCOMPARE */
	List	   *operName;		/* originally specified operator name */
	Node	   *subselect;		/* subselect as Query* or raw parsetree */
	int			location;		/* token location, or -1 if unknown */
} SubLink;

```

**MaterialState**
Material狀態
```
/* ----------------
 *	 MaterialState information
 *
 *		materialize nodes are used to materialize the results
 *		of a subplan into a temporary file.
 *		materialize節點用於物化subplan的結果為臨時檔案。
 *
 *		ss.ss_ScanTupleSlot refers to output of underlying plan.
 *		ss.ss_ScanTupleSlot指向underlyling plan的輸出（subplan）
 * ----------------
 */
typedef struct MaterialState
{
	ScanState	ss;				/* its first field is NodeTag */
	int			eflags;			/* 傳遞給tuplestore的capability標記；capability flags to pass to tuplestore */
	bool		eof_underlying; /* 已經到達underlying plan的末尾？reached end of underlying plan? */
	Tuplestorestate *tuplestorestate;
} MaterialState;

```

### 二、原始碼解讀
****
```

/* ----------------------------------------------------------------
 *		ExecMaterial
 *
 *		As long as we are at the end of the data collected in the tuplestore,
 *		we collect one new row from the subplan on each call, and stash it
 *		aside in the tuplestore before returning it.  The tuplestore is
 *		only read if we are asked to scan backwards, rescan, or mark/restore.
 *      只要在tuplestore中資料收集結束時，就會在每次呼叫時從subplan中收集一條新行，
 *      並在返回之前將其儲存在tuplestore中。
 *      只要在往後掃描、重新掃描或標記/恢復時tuplestore才會讀取。
 *
 * ----------------------------------------------------------------
 */
static TupleTableSlot *			/* 從subplan中返回的結果；result tuple from subplan */
ExecMaterial(PlanState *pstate)
{
	MaterialState *node = castNode(MaterialState, pstate);//物化節點
	EState	   *estate;//執行期狀態
	ScanDirection dir;//掃描方向
	bool		forward;//是否往前掃描
	Tuplestorestate *tuplestorestate;//Tuplestorestate結構體指標
	bool		eof_tuplestore;//是否完成?
	TupleTableSlot *slot;//儲存元組的slot

CHECK_FOR_INTERRUPTS();

/*
	 * get state info from node
	 * 從物化節點中獲取相關資訊
	 */
	estate = node->ss.ps.state;
	dir = estate->es_direction;//方向
	forward = ScanDirectionIsForward(dir);//是否往前掃描
	tuplestorestate = node->tuplestorestate;

/*
	 * If first time through, and we need a tuplestore, initialize it.
	 * 第一次，需要tuplestore並初始化
	 */
	if (tuplestorestate == NULL && node->eflags != 0)
	{
		tuplestorestate = tuplestore_begin_heap(true, false, work_mem);
		tuplestore_set_eflags(tuplestorestate, node->eflags);
		if (node->eflags & EXEC_FLAG_MARK)
		{
			/*
			 * Allocate a second read pointer to serve as the mark. We know it
			 * must have index 1, so needn't store that.
			 * 分配用於mark的讀指標
			 */
			int			ptrno PG_USED_FOR_ASSERTS_ONLY;

ptrno = tuplestore_alloc_read_pointer(tuplestorestate,
												  node->eflags);
			Assert(ptrno == 1);
		}
		node->tuplestorestate = tuplestorestate;
	}

/*
	 * If we are not at the end of the tuplestore, or are going backwards, try
	 * to fetch a tuple from tuplestore.
	 * 如果不在tuplestore的末尾或者正在往後掃描，嘗試從tuplestore中提取一個元組
	 */
	eof_tuplestore = (tuplestorestate == NULL) ||
		tuplestore_ateof(tuplestorestate);

if (!forward && eof_tuplestore)
	{
		if (!node->eof_underlying)
		{
			/*
			 * When reversing direction at tuplestore EOF, the first
			 * gettupleslot call will fetch the last-added tuple; but we want
			 * to return the one before that, if possible. So do an extra
			 * fetch.
			 * 在EOF處反轉方向，第一次的gettupleslot呼叫會提取最後新增的元組；
			 * 但如可能，希望返回在此之前的元組，執行額外的提取操作。
			 */
			if (!tuplestore_advance(tuplestorestate, forward))
				return NULL;	/* the tuplestore must be empty */
		}
		eof_tuplestore = false;
	}

/*
	 * If we can fetch another tuple from the tuplestore, return it.
	 * 如能從tuplestore中提取另外一個tuple，返回
	 */
	slot = node->ss.ps.ps_ResultTupleSlot;
	if (!eof_tuplestore)
	{
		if (tuplestore_gettupleslot(tuplestorestate, forward, false, slot))
			return slot;
		if (forward)
			eof_tuplestore = true;
	}

/*
	 * If necessary, try to fetch another row from the subplan.
	 * 如需要（tuplestore末尾），嘗試從subplan中提取另外一行
	 *
	 * Note: the eof_underlying state variable exists to short-circuit further
	 * subplan calls.  It's not optional, unfortunately, because some plan
	 * node types are not robust about being called again when they've already
	 * returned NULL.
	 */
	if (eof_tuplestore && !node->eof_underlying)
	{
		PlanState  *outerNode;
		TupleTableSlot *outerslot;

/*
		 * We can only get here with forward==true, so no need to worry about
		 * which direction the subplan will go.
		 */
		outerNode = outerPlanState(node);
		outerslot = ExecProcNode(outerNode);
		if (TupIsNull(outerslot))
		{
			node->eof_underlying = true;
			return NULL;
		}

/*
		 * Append a copy of the returned tuple to tuplestore.  NOTE: because
		 * the tuplestore is certainly in EOF state, its read position will
		 * move forward over the added tuple.  This is what we want.
		 * 追加返回的元組到tuplestore中。
		 * 注意：因為tuplestore當前處於EOF狀態，讀取的位置會前移至已新增的tuple前面，這是我們希望看到的。
		 */
		if (tuplestorestate)
			tuplestore_puttupleslot(tuplestorestate, outerslot);

ExecCopySlot(slot, outerslot);
		return slot;
	}

/*
	 * Nothing left ...
	 */
	return ExecClearTuple(slot);
}

```

### 三、跟蹤分析
執行SQL：
```
[pg12@localhost ~]$ psql -d testdb
Timing is on.
Expanded display is used automatically.
psql (12.0)
Type "help" for help.

[local]:5432 pg12@testdb=# 
[local]:5432 pg12@testdb=# select * from tbl;
 id | value 
----+-------
  1 |     2
(1 row)

Time: 2.678 ms
[local]:5432 pg12@testdb=# select count(*) from t_big_null;
  count   
----------
 10000001
(1 row)

Time: 679.972 ms
[local]:5432 pg12@testdb=# analyze tbl;
ANALYZE
Time: 64.442 ms
[local]:5432 pg12@testdb=# analyze t_big_null;
ANALYZE
Time: 434.702 ms
[local]:5432 pg12@testdb=# 
[local]:5432 pg12@testdb=# select pg_backend_pid();
 pg_backend_pid 
----------------
          18758
(1 row)

Time: 1.990 ms
[local]:5432 pg12@testdb=# select * from tbl a where a.id not in (select b.id from t_big_null b);

```
啟動gdb跟蹤
```
(gdb) b ExecMaterial
Breakpoint 1 at 0x720edb: file nodeMaterial.c, line 41.
(gdb) c
Continuing.

Breakpoint 1, ExecMaterial (pstate=0x1230128) at nodeMaterial.c:41
41		MaterialState *node = castNode(MaterialState, pstate);
(gdb) 
```
輸入引數
```
(gdb) p *pstate
$4 = {type = T_MaterialState, plan = 0x1211858, state = 0x122fe88, 
  ExecProcNode = 0x720ecf <execmaterial>, ExecProcNodeReal = 0x720ecf <execmaterial>, 
  instrument = 0x0, worker_instrument = 0x0, worker_jit_instrument = 0x0, qual = 0x0, 
  lefttree = 0x1230240, righttree = 0x0, initPlan = 0x0, subPlan = 0x0, chgParam = 0x0, 
  ps_ResultTupleDesc = 0x1230660, ps_ResultTupleSlot = 0x1230778, ps_ExprContext = 0x0, 
  ps_ProjInfo = 0x0, scandesc = 0x1230548, scanops = 0xc3e720 <ttsopsminimaltuple>, 
  outerops = 0x0, innerops = 0x0, resultops = 0xc3e720 <ttsopsminimaltuple>, 
  scanopsfixed = true, outeropsfixed = false, inneropsfixed = false, 
  resultopsfixed = true, scanopsset = true, outeropsset = false, inneropsset = false, 
  resultopsset = true}
(gdb) 
```
MaterialState結構體指標資料
```
(gdb) p *node
$1 = {ss = {ps = {type = T_MaterialState, plan = 0x1211858, state = 0x122fe88, 
      ExecProcNode = 0x720ecf <execmaterial>, ExecProcNodeReal = 0x720ecf <execmaterial>, 
      instrument = 0x0, worker_instrument = 0x0, worker_jit_instrument = 0x0, qual = 0x0, 
      lefttree = 0x1230240, righttree = 0x0, initPlan = 0x0, subPlan = 0x0, 
      chgParam = 0x0, ps_ResultTupleDesc = 0x1230660, ps_ResultTupleSlot = 0x1230778, 
      ps_ExprContext = 0x0, ps_ProjInfo = 0x0, scandesc = 0x1230548, 
      scanops = 0xc3e720 <ttsopsminimaltuple>, outerops = 0x0, innerops = 0x0, 
      resultops = 0xc3e720 <ttsopsminimaltuple>, scanopsfixed = true, 
      outeropsfixed = false, inneropsfixed = false, resultopsfixed = true, 
      scanopsset = true, outeropsset = false, inneropsset = false, resultopsset = true}, 
    ss_currentRelation = 0x0, ss_currentScanDesc = 0x0, ss_ScanTupleSlot = 0x1230838}, 
  eflags = 2, eof_underlying = false, tuplestorestate = 0x0}
(gdb) p *node->ss->ps->plan
$2 = {type = T_Material, startup_cost = 0, total_cost = 233310.685, plan_rows = 9999979, 
  plan_width = 4, parallel_aware = false, parallel_safe = true, plan_node_id = 1, 
  targetlist = 0x1257600, qual = 0x0, lefttree = 0x1210f58, righttree = 0x0, 
  initPlan = 0x0, extParam = 0x0, allParam = 0x0}
(gdb) 
```
執行期資訊和方向
```
(gdb) p *estate
$5 = {type = T_EState, es_direction = ForwardScanDirection, es_snapshot = 0x1164d50, 
  es_crosscheck_snapshot = 0x0, es_range_table = 0x1257328, 
  es_range_table_array = 0x12300d8, es_range_table_size = 2, es_relations = 0x1230100, 
  es_rowmarks = 0x0, es_plannedstmt = 0x1257748, 
  es_sourceText = 0x113cd88 "select * from tbl a where a.id not in (select b.id from t_big_null b);", es_junkFilter = 0x0, es_output_cid = 0, es_result_relations = 0x0, 
  es_num_result_relations = 0, es_result_relation_info = 0x0, 
  es_root_result_relations = 0x0, es_num_root_result_relations = 0, 
  es_partition_directory = 0x0, es_tuple_routing_result_relations = 0x0, 
  es_trig_target_relations = 0x0, es_param_list_info = 0x0, 
  es_param_exec_vals = 0x12300a0, es_queryEnv = 0x0, es_query_cxt = 0x122fd70, 
  es_tupleTable = 0x1230510, es_processed = 0, es_top_eflags = 16, es_instrument = 0, 
  es_finished = false, es_exprcontexts = 0x1230418, es_subplanstates = 0x1230920, 
  es_auxmodifytables = 0x0, es_per_tuple_exprcontext = 0x0, es_epq_active = 0x0, 
  es_use_parallel_mode = false, es_query_dsa = 0x0, es_jit_flags = 25, es_jit = 0x0, 
  es_jit_worker_instr = 0x0}
(gdb) p dir
$6 = ForwardScanDirection
(gdb) 
```
初始化tuplestore
```
(gdb) n
64			tuplestorestate = tuplestore_begin_heap(true, false, work_mem);
(gdb) n
65			tuplestore_set_eflags(tuplestorestate, node->eflags);
(gdb) p *tuplestorestate
$7 = {status = TSS_INMEM, eflags = 6, backward = false, interXact = false, 
  truncated = false, availMem = 4177896, allowedMem = 4194304, tuples = 0, myfile = 0x0, 
  context = 0x122fd70, resowner = 0x116e308, copytup = 0xaba7bd <copytup_heap>, 
  writetup = 0xaba811 <writetup_heap>, readtup = 0xaba9d9 <readtup_heap>, 
  memtuples = 0x1219e60, memtupdeleted = 0, memtupcount = 0, memtupsize = 2048, 
  growmemtuples = true, readptrs = 0x123ca50, activeptr = 0, readptrcount = 1, 
  readptrsize = 8, writepos_file = 0, writepos_offset = 0}
(gdb) n
66			if (node->eflags & EXEC_FLAG_MARK)
(gdb) 
78			node->tuplestorestate = tuplestorestate;
(gdb) 
85		eof_tuplestore = (tuplestorestate == NULL) ||
(gdb) p *tuplestorestate
$8 = {status = TSS_INMEM, eflags = 2, backward = false, interXact = false, 
  truncated = false, availMem = 4177896, allowedMem = 4194304, tuples = 0, myfile = 0x0, 
  context = 0x122fd70, resowner = 0x116e308, copytup = 0xaba7bd <copytup_heap>, 
  writetup = 0xaba811 <writetup_heap>, readtup = 0xaba9d9 <readtup_heap>, 
  memtuples = 0x1219e60, memtupdeleted = 0, memtupcount = 0, memtupsize = 2048, 
  growmemtuples = true, readptrs = 0x123ca50, activeptr = 0, readptrcount = 1, 
  readptrsize = 8, writepos_file = 0, writepos_offset = 0}
(gdb) 
```
既不是往後掃描也沒有到達EOF
```
(gdb) n
86			tuplestore_ateof(tuplestorestate);
(gdb) 
85		eof_tuplestore = (tuplestorestate == NULL) ||
(gdb) 
88		if (!forward && eof_tuplestore)
(gdb) p eof_tuplestore
$9 = false
(gdb) p forward
$10 = true
(gdb) 
```
如能從tuplestore中提取另外一個tuple，則返回此slot
```
(gdb) n
107		slot = node->ss.ps.ps_ResultTupleSlot;
(gdb) 
108		if (!eof_tuplestore)
(gdb) p *slot
$11 = {type = T_TupleTableSlot, tts_flags = 18, tts_nvalid = 0, 
  tts_ops = 0xc3e720 <ttsopsminimaltuple>, tts_tupleDescriptor = 0x1230660, 
  tts_values = 0x12307e8, tts_isnull = 0x12307f0, tts_mcxt = 0x122fd70, tts_tid = {
    ip_blkid = {bi_hi = 65535, bi_lo = 65535}, ip_posid = 0}, tts_tableOid = 0}
(gdb) p slot->tts_values[0]
$12 = 0
(gdb) n
110			if (tuplestore_gettupleslot(tuplestorestate, forward, false, slot))
(gdb) 
```
如掃描方向為往前，則設定eof_tuplestore為T，填充tuple到tuplestore中
```
112			if (forward)
(gdb) 
113				eof_tuplestore = true;
(gdb) 
```
如需要（處於tuplestore末尾），嘗試從subplan（掃描t_big_null）中提取另外一行
```
124		if (eof_tuplestore && !node->eof_underlying)
(gdb) p node->eof_underlying
$13 = false
(gdb) n
133			outerNode = outerPlanState(node);
(gdb) n
134			outerslot = ExecProcNode(outerNode);
(gdb) 
135			if (TupIsNull(outerslot))
(gdb) p *outerNode
$14 = {type = T_SeqScanState, plan = 0x1210f58, state = 0x122fe88, 
  ExecProcNode = 0x72b904 <execseqscan>, ExecProcNodeReal = 0x72b904 <execseqscan>, 
  instrument = 0x0, worker_instrument = 0x0, worker_jit_instrument = 0x0, qual = 0x0, 
  lefttree = 0x0, righttree = 0x0, initPlan = 0x0, subPlan = 0x0, chgParam = 0x0, 
  ps_ResultTupleDesc = 0x1230548, ps_ResultTupleSlot = 0x0, ps_ExprContext = 0x1230358, 
  ps_ProjInfo = 0x0, scandesc = 0x7f6ec53386a8, 
  scanops = 0xc3e780 <ttsopsbufferheaptuple>, outerops = 0x0, innerops = 0x0, 
  resultops = 0xc3e780 <ttsopsbufferheaptuple>, scanopsfixed = true, 
  outeropsfixed = false, inneropsfixed = false, resultopsfixed = true, scanopsset = true, 
  outeropsset = false, inneropsset = false, resultopsset = true}
(gdb) p *outerslot
$15 = {type = T_TupleTableSlot, tts_flags = 16, tts_nvalid = 0, 
  tts_ops = 0xc3e780 <ttsopsbufferheaptuple>, tts_tupleDescriptor = 0x7f6ec53386a8, 
  tts_values = 0x12304c0, tts_isnull = 0x12304c8, tts_mcxt = 0x122fd70, tts_tid = {
    ip_blkid = {bi_hi = 0, bi_lo = 44240}, ip_posid = 1}, tts_tableOid = 49155}
(gdb) p outerslot->tts_values[0]
$16 = 0
(gdb) p outerslot->tts_values[1]
$17 = 0
(gdb) 
###
[local]:5432 pg12@testdb=# select oid,relname from pg_class where oid = 49155;
  oid  |  relname   
-------+------------
 49155 | t_big_null
(1 row)
###
```
複製到tuplestore中，返回slot
```
(gdb) n
146			if (tuplestorestate)
(gdb) 
147				tuplestore_puttupleslot(tuplestorestate, outerslot);
(gdb) 
149			ExecCopySlot(slot, outerslot);
(gdb) 
150			return slot;
(gdb) p *slot
$18 = {type = T_TupleTableSlot, tts_flags = 20, tts_nvalid = 0, 
  tts_ops = 0xc3e720 <ttsopsminimaltuple>, tts_tupleDescriptor = 0x1230660, 
  tts_values = 0x12307e8, tts_isnull = 0x12307f0, tts_mcxt = 0x122fd70, tts_tid = {
    ip_blkid = {bi_hi = 65535, bi_lo = 65535}, ip_posid = 0}, tts_tableOid = 0}
(gdb) p *slot->tts_values
$19 = 0
(gdb) 
```
繼續執行
```
...
(gdb) p slot->tts_values[0]
$24 = 9998243
(gdb) c
Continuing.

Breakpoint 1, ExecMaterial (pstate=0x1230128) at nodeMaterial.c:41
41		MaterialState *node = castNode(MaterialState, pstate);
(gdb) n
49		CHECK_FOR_INTERRUPTS();
(gdb) 
54		estate = node->ss.ps.state;
(gdb) 
55		dir = estate->es_direction;
(gdb) 
56		forward = ScanDirectionIsForward(dir);
(gdb) 
57		tuplestorestate = node->tuplestorestate;
(gdb) 
62		if (tuplestorestate == NULL && node->eflags != 0)
(gdb) 
85		eof_tuplestore = (tuplestorestate == NULL) ||
(gdb) 
86			tuplestore_ateof(tuplestorestate);
(gdb) 
85		eof_tuplestore = (tuplestorestate == NULL) ||
(gdb) 
88		if (!forward && eof_tuplestore)
(gdb) 
107		slot = node->ss.ps.ps_ResultTupleSlot;
(gdb) 
108		if (!eof_tuplestore)
(gdb) 
124		if (eof_tuplestore && !node->eof_underlying)
(gdb) 
133			outerNode = outerPlanState(node);
(gdb) 
134			outerslot = ExecProcNode(outerNode);
(gdb) 
135			if (TupIsNull(outerslot))
(gdb) 
146			if (tuplestorestate)
(gdb) 
147				tuplestore_puttupleslot(tuplestorestate, outerslot);
(gdb) 
149			ExecCopySlot(slot, outerslot);
(gdb) 
150			return slot;
(gdb) p slot->tts_values[0]
$25 = 9998244
(gdb) 
...
```

**DONE**

### 四、參考資料
N/A</ttsopsminimaltuple></ttsopsbufferheaptuple></ttsopsbufferheaptuple></ttsopsbufferheaptuple></execseqscan></execseqscan></ttsopsminimaltuple></readtup_heap></writetup_heap></copytup_heap></readtup_heap></writetup_heap></copytup_heap></ttsopsminimaltuple></ttsopsminimaltuple></execmaterial></execmaterial></ttsopsminimaltuple></ttsopsminimaltuple></execmaterial></execmaterial>

PostgreSQL 原始碼解讀（231）- 查詢#124(NOT IN實現#2)

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