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本篇内容介绍了“怎么使用PostgreSQ中的ExecMaterial函数”的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！
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SubPlanState
子计划运行期状态
/* ----------------
* 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; /* 组合表达式状态；state of combining expression */
List *args; /* 参数表达式状态；states of argument expression(s) */
HeapTuple curTuple; /* subplan最近的元组；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; /* 投影后的子查询描述符；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
子查询计划
/*
* 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.)
* 查询规划器在完成子查询的规划后使用SubPlan节点替换表达式树中的SubLink节点。
* SubPlan引用了存储在高层PlannedStmt中的subplans链表中的sub-plantree。
* （避免使用直接链接，从而使得拷贝表达式树相对比较简单）
*
* 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.
* 常规情况下，testexpr指向用于组合操作的可执行表达式（OpExpr、OpExprs的AND/OR树或者RowCompareExpr）；
* 左参数是原始的左表达式，右参数是PARAM_EXEC参数节点用以表示子查询的输出。
* 与原始SubLink节点的testexpr具有相同的表达式树，但PARAM_SUBLINK节点则使用合适的已编号PARAM_EXEC节点替代。
*
* 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.
* 如果子查询成了initplan而不是subplan，可执行的表达式是外层plan表达式树的一部分。
* 这种情况下，testexpr为NULL以避免重复。
*
* 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.)
* 规划器还派生了需要传入和传出子计划的值的链表。
* 输入值标识位表达式的“args”链表，在外层查询上下文中进行解析。
* （这些args通常是Vars，但原则上它们可以是任意表达式）
* 这些值以parParam为索引给全局PARAM_EXEC参数赋值。
* setParam是PARAM_EXEC参数链表，通过子查询（如为initplan）计算所得。
* 它们按子查询输出列的位置进行排序组织为链表形式。
* （parParam和setParam是整型链表，而不是Bitmapsets链表）
*
* 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.
* 同时，规划器计算SubPlan启动和每次调用的成本。注意：包括子查询正常解析testexpr的成本以及哈希表管理成本。
*/
typedef struct SubPlan
{
Expr xpr;//表达式
/* Fields copied from original SubLink: */
//从SubLink中拷贝而来
SubLinkType subLinkType; /* see above */
/* The combining operators, transformed to an executable expression: */
//组合操作符,转换为可执行的表达式
Node *testexpr; /* OpExpr or RowCompareExpr expression tree */
List *paramIds; /* 参数IDs;IDs of Params embedded in the above */
/* Identification of the Plan tree to use: */
//Plan tree标识
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标识
char *plan_name; /* A name assigned during planning */
/* Extra data useful for determining subplan's output type: */
//用于确定subplan输出类型的额外信息
Oid firstColType; /* subplan结果的第一个列类型;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: */
//执行阶段的相关信息
bool useHashTable; /* 是否使用哈希表存储子查询输出;true to store subselect output in a hash
* table (implies we are doing "IN") */
bool unknownEqFalse; /* 如OK为T,如为未知则为F;快速处理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; /* 是否并行安全?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: */
//用于给子查询传入和传出参数的信息
/* setParam and parParam are lists of integers (param IDs) */
//setParam和parParam是整型链表(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值进行传递的表达式；exprs to pass as parParam values */
/* Estimated execution costs: */
//估算执行成本
Cost startup_cost; /* one-time setup cost */
Cost per_call_cost; /* cost for each subplan evaluation */
} SubPlan;SubLinkType
SubLink类型
/*
* 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结构体
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状态
/* ----------------
* MaterialState information
*
* materialize nodes are used to materialize the results
* of a subplan into a temporary file.
* materialize节点用于物化subplan的结果为临时文件。
*
* ss.ss_ScanTupleSlot refers to output of underlying plan.
* ss.ss_ScanTupleSlot指向underlyling plan的输出（subplan）
* ----------------
*/
typedef struct MaterialState
{
ScanState ss; /* its first field is NodeTag */
int eflags; /* 传递给tuplestore的capability标记；capability flags to pass to tuplestore */
bool eof_underlying; /* 已经到达underlying plan的末尾？reached end of underlying plan? */
Tuplestorestate *tuplestorestate;
} MaterialState;/* ----------------------------------------------------------------
* 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中数据收集结束时，就会在每次调用时从subplan中收集一条新行，
* 并在返回之前将其保存在tuplestore中。
* 只要在往后扫描、重新扫描或标记/恢复时tuplestore才会读取。
*
* ----------------------------------------------------------------
*/
static TupleTableSlot * /* 从subplan中返回的结果；result tuple from subplan */
ExecMaterial(PlanState *pstate)
{
MaterialState *node = castNode(MaterialState, pstate);//物化节点
EState *estate;//运行期状态
ScanDirection dir;//扫描方向
bool forward;//是否往前扫描
Tuplestorestate *tuplestorestate;//Tuplestorestate结构体指针
bool eof_tuplestore;//是否完成?
TupleTableSlot *slot;//存储元组的slot
CHECK_FOR_INTERRUPTS();
/*
* get state info from node
* 从物化节点中获取相关信息
*/
estate = node->ss.ps.state;
dir = estate->es_direction;//方向
forward = ScanDirectionIsForward(dir);//是否往前扫描
tuplestorestate = node->tuplestorestate;
/*
* If first time through, and we need a tuplestore, initialize it.
* 第一次，需要tuplestore并初始化
*/
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.
* 分配用于mark的读指针
*/
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的末尾或者正在往后扫描，尝试从tuplestore中提取一个元组
*/
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处反转方向，第一次的gettupleslot调用会提取最后添加的元组；
* 但如可能，希望返回在此之前的元组，执行额外的提取操作。
*/
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.
* 如能从tuplestore中提取另外一个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），尝试从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.
* 追加返回的元组到tuplestore中。
* 注意：因为tuplestore当前处于EOF状态，读取的位置会前移至已添加的tuple前面，这是我们希望看到的。
*/
if (tuplestorestate)
tuplestore_puttupleslot(tuplestorestate, outerslot);
ExecCopySlot(slot, outerslot);
return slot;
}
/*
* Nothing left ...
*/
return ExecClearTuple(slot);
}执行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);
启动gdb跟踪
(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)
输入参数
(gdb) p *pstate
$4 = {type = T_MaterialState, plan = 0x1211858, state = 0x122fe88,
ExecProcNode = 0x720ecf , ExecProcNodeReal = 0x720ecf ,
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 ,
outerops = 0x0, innerops = 0x0, resultops = 0xc3e720 ,
scanopsfixed = true, outeropsfixed = false, inneropsfixed = false,
resultopsfixed = true, scanopsset = true, outeropsset = false, inneropsset = false,
resultopsset = true}
(gdb) MaterialState结构体指针数据
(gdb) p *node
$1 = {ss = {ps = {type = T_MaterialState, plan = 0x1211858, state = 0x122fe88,
ExecProcNode = 0x720ecf , ExecProcNodeReal = 0x720ecf ,
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 , outerops = 0x0, innerops = 0x0,
resultops = 0xc3e720 , 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) 运行期信息和方向
(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 ,
writetup = 0xaba811 , readtup = 0xaba9d9 ,
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 ,
writetup = 0xaba811 , readtup = 0xaba9d9 ,
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) 既不是往后扫描也没有到达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)
如能从tuplestore中提取另外一个tuple，则返回此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 , 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) 如扫描方向为往前，则设置eof_tuplestore为T，填充tuple到tuplestore中
112 if (forward) (gdb) 113 eof_tuplestore = true; (gdb)
如需要（处于tuplestore末尾），尝试从subplan（扫描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 , ExecProcNodeReal = 0x72b904 ,
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 , outerops = 0x0, innerops = 0x0,
resultops = 0xc3e780 , 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 , 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)
### 拷贝到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 , 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) 继续执行
... (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) ...
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