本节简单解释了PostgreSQL NOT IN在执行时为何会出现时快时慢的现象。
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测试数据如下：
[local]:5432 pg12@testdb=# select count(*) from tbl;
count
-------
1
(1 row)
Time: 6.009 ms
[local]:5432 pg12@testdb=# select count(*) from t_big_null;
count
----------
10000001
(1 row)
Time: 633.248 ms
[local]:5432 pg12@testdb=# \d tbl
Table "public.tbl"
Column | Type | Collation | Nullable | Default
--------+---------+-----------+----------+---------
id | integer | | not null |
value | integer | | not null |
Indexes:
"tbl_pkey" PRIMARY KEY, btree (id)
Rules:
rule_tbl_update AS
ON INSERT TO tbl
WHERE (EXISTS ( SELECT tbl_1.id,
tbl_1.value
FROM tbl tbl_1
WHERE tbl_1.id = new.id)) DO INSTEAD UPDATE tbl SET value = tbl.value + 1
WHERE tbl.id = new.id
[local]:5432 pg12@testdb=# \d t_big_null
Table "public.t_big_null"
Column | Type | Collation | Nullable | Default
--------+---------+-----------+----------+---------
id | integer | | |
[local]:5432 pg12@testdb=#
注意tbl表只有一行数据(id = 1)，而t_big_null表在插入”id = 1”这一行时有意放在最后才插入
truncate table t_big_null;
insert into t_big_null select generate_series(2,10000000);
insert into t_big_null values(1);
一、数据结构
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)
* 我们使用SubLink表示在表达式中出现的子查询，在某些情况下组合操作符会出现在SubLink之上。
* subLinkType表示表达式的形式：
* 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.
* 对于ALL,ANY和ROWCOMPARE,左操作符是与子查询目标链表长度一致的表达式链表。
* ROWCOMPARE通常有超过一个条目的链表；如果子查询刚好只有一个目标列，那么解析器会创建EXPR_SUBLINK
* （同时所有在子查询之上的操作符会单独表示）
* ROWCOMPARE, EXPR, 和MULTIEXPR要求子查询至少输出一行（如返回0行，则结果为NULL）。
* ALL,ANY和ROWCOMPARE要求组合操作符输出布尔型结果。
* ALL/ANY使用AND/OR语义来组合每一行的结果。
*
* 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.
* SubLink归类为Expr节点，但实际上并不是可执行的，必须在计划阶段通过SubPlan替代。
*
* 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.
* 注意：在gram.y的裸输出中，testexpr只包含左表达式的裸形式，operName是组合操作符的字符串名称。
* 同时，子查询是裸parsetree。在解析分析期间，
* 解析器转换testexpr为完整的布尔表达式用于比较左操作符值与PARAM_SUBLINK节点所代表的子查询输出列值。
* 子查询会转换为Query结构体。
* 在已存储的规则和重写时可见的表示形式。
*
* In EXISTS, EXPR, MULTIEXPR, and ARRAY SubLinks, testexpr and operName
* are unused and are always null.
* 在EXISTS/EXPR/MULTEXPR/ARRAY SubLinks中，testexpr和operName不再使用通常是NULL值。
*
* 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.
* subLinkId当前只用于MULTIEXPR，在其他SubLinks中取值为0.
* 该数字标识了在UPDATE语句SET链表中不同的多个赋值子查询。
* 只有在特定的targetlist内是唯一的。
* 出现在tlist其他地方的PARAM_MULTIEXPR参数依赖于MULTIEXPR的输出列。
*
* The CTE_SUBLINK case never occurs in actual SubLink nodes, but it is used
* in SubPlans generated for WITH subqueries.
* CTE_SUBLINK不会出现在实际的SubLink节点中，但用于WITH子查询所产生的SubPlans中。
*/
typedef enum SubLinkType
{
EXISTS_SUBLINK,
ALL_SUBLINK,
ANY_SUBLINK,
ROWCOMPARE_SUBLINK,
EXPR_SUBLINK,
MULTIEXPR_SUBLINK,
ARRAY_SUBLINK,
CTE_SUBLINK /* 仅用于SubPlans中；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;
Tuplestorestate
Tuplestore相关操作的私有状态。
/*
* Possible states of a Tuplestore object. These denote the states that
* persist between calls of Tuplestore routines.
*/
typedef enum
{
TSS_INMEM, /* Tuples still fit in memory */
TSS_WRITEFILE, /* Writing to temp file */
TSS_READFILE /* Reading from temp file */
} TupStoreStatus;
/*
* Private state of a Tuplestore operation.
*/
struct Tuplestorestate
{
TupStoreStatus status; /* 状态枚举值；enumerated value as shown above */
int eflags; /* capability flags (OR of pointers' flags) */
bool backward; /* store extra length words in file? */
bool interXact; /* keep open through transactions? */
bool truncated; /* tuplestore_trim has removed tuples? */
int64 availMem; /* remaining memory available, in bytes */
int64 allowedMem; /* total memory allowed, in bytes */
int64 tuples; /* number of tuples added */
BufFile *myfile; /* underlying file, or NULL if none */
MemoryContext context; /* memory context for holding tuples */
ResourceOwner resowner; /* resowner for holding temp files */
/*
* These function pointers decouple the routines that must know what kind
* of tuple we are handling from the routines that don't need to know it.
* They are set up by the tuplestore_begin_xxx routines.
*
* (Although tuplestore.c currently only supports heap tuples, I've copied
* this part of tuplesort.c so that extension to other kinds of objects
* will be easy if it's ever needed.)
*
* Function to copy a supplied input tuple into palloc'd space. (NB: we
* assume that a single pfree() is enough to release the tuple later, so
* the representation must be "flat" in one palloc chunk.) state->availMem
* must be decreased by the amount of space used.
*/
void *(*copytup) (Tuplestorestate *state, void *tup);
/*
* Function to write a stored tuple onto tape. The representation of the
* tuple on tape need not be the same as it is in memory; requirements on
* the tape representation are given below. After writing the tuple,
* pfree() it, and increase state->availMem by the amount of memory space
* thereby released.
*/
void (*writetup) (Tuplestorestate *state, void *tup);
/*
* Function to read a stored tuple from tape back into memory. 'len' is
* the already-read length of the stored tuple. Create and return a
* palloc'd copy, and decrease state->availMem by the amount of memory
* space consumed.
*/
void *(*readtup) (Tuplestorestate *state, unsigned int len);
/*
* This array holds pointers to tuples in memory if we are in state INMEM.
* In states WRITEFILE and READFILE it's not used.
*
* When memtupdeleted > 0, the first memtupdeleted pointers are already
* released due to a tuplestore_trim() operation, but we haven't expended
* the effort to slide the remaining pointers down. These unused pointers
* are set to NULL to catch any invalid accesses. Note that memtupcount
* includes the deleted pointers.
*/
void **memtuples; /* array of pointers to palloc'd tuples */
int memtupdeleted; /* the first N slots are currently unused */
int memtupcount; /* number of tuples currently present */
int memtupsize; /* allocated length of memtuples array */
bool growmemtuples; /* memtuples' growth still underway? */
/*
* These variables are used to keep track of the current positions.
*
* In state WRITEFILE, the current file seek position is the write point;
* in state READFILE, the write position is remembered in writepos_xxx.
* (The write position is the same as EOF, but since BufFileSeek doesn't
* currently implement SEEK_END, we have to remember it explicitly.)
*/
TSReadPointer *readptrs; /* array of read pointers */
int activeptr; /* index of the active read pointer */
int readptrcount; /* number of pointers currently valid */
int readptrsize; /* allocated length of readptrs array */
int writepos_file; /* file# (valid if READFILE state) */
off_t writepos_offset; /* offset (valid if READFILE state) */
};
#define COPYTUP(state,tup) ((*(state)->copytup) (state, tup))
#define WRITETUP(state,tup) ((*(state)->writetup) (state, tup))
#define READTUP(state,len) ((*(state)->readtup) (state, len))
#define LACKMEM(state) ((state)->availMem < 0)
#define USEMEM(state,amt) ((state)->availMem -= (amt))
#define FREEMEM(state,amt) ((state)->availMem += (amt))
TSReadPointer
tuplestore读指针
/*
* Possible states of a Tuplestore object. These denote the states that
* persist between calls of Tuplestore routines.
*/
typedef enum
{
TSS_INMEM, /* Tuples still fit in memory */
TSS_WRITEFILE, /* Writing to temp file */
TSS_READFILE /* Reading from temp file */
} TupStoreStatus;
/*
* State for a single read pointer. If we are in state INMEM then all the
* read pointers' "current" fields denote the read positions. In state
* WRITEFILE, the file/offset fields denote the read positions. In state
* READFILE, inactive read pointers have valid file/offset, but the active
* read pointer implicitly has position equal to the temp file's seek position.
*
* Special case: if eof_reached is true, then the pointer's read position is
* implicitly equal to the write position, and current/file/offset aren't
* maintained. This way we need not update all the read pointers each time
* we write.
*/
typedef struct
{
int eflags; /* capability flags */
bool eof_reached; /* read has reached EOF */
int current; /* next array index to read */
int file; /* temp file# */
off_t offset; /* byte offset in file */
} TSReadPointer;
二、源码解读
NOT IN在实际执行时会转换为ALL_SUBLINK，执行的快慢取决于什么时候会碰到符合条件的记录，一旦遇到马上返回。因此，SQL的执行时间与数据表的扫描顺序有紧密的关系，符合条件的行越早出现，程序越早返回，需要的时间越短。
相关代码如下：
...
//解析表达式
rowresult = ExecEvalExprSwitchContext(node->testexpr, econtext,
&rownull);
if (subLinkType == ANY_SUBLINK)
{
//ANY : 使用OR语义组合
/* combine across rows per OR semantics */
if (rownull)
*isNull = true;
else if (DatumGetBool(rowresult))
{
result = BoolGetDatum(true);
*isNull = false;
break; /* needn't look at any more rows */
}
}
如上代码所示，在全表扫描物化的时候一旦textexpr表达式测试到其中一行满足条件，那么就会马上退出循环，而这一行如果非常幸运的出现在扫描的最开始的地方，那执行时间将会很快（扫描几个数据块 vs 全表扫描）。
新建一张表，插入2条记录，其中id = 2的行出现在block编号最小的地方，而id = 1出现在block编号最大的地方，这时候pg就会出现时快时慢的情况，两者相差3个数量级。
[local]:5432 pg12@testdb=# create table tbl3(id int);
CREATE TABLE
Time: 1.852 ms
[local]:5432 pg12@testdb=# insert into tbl3 values(1);
INSERT 0 1
Time: 1.276 ms
[local]:5432 pg12@testdb=# insert into tbl3 values(2);
INSERT 0 1
Time: 1.089 ms
[local]:5432 pg12@testdb=# select * from tbl3 where id not in (select b.id from t_big_null b);
id
----
(0 rows)
Time: 3.676 ms
[local]:5432 pg12@testdb=# select * from tbl3 where id not in (select b.id from t_big_null b);
id
----
(0 rows)
Time: 4925.893 ms (00:04.926)
[local]:5432 pg12@testdb=# select * from tbl3 where id not in (select b.id from t_big_null b);
id
----
(0 rows)
Time: 2.858 ms
[local]:5432 pg12@testdb=# select * from tbl3 where id not in (select b.id from t_big_null b);
id
----
(0 rows)
Time: 4588.436 ms (00:04.588)
[local]:5432 pg12@testdb=# select * from tbl3 where id not in (select b.id from t_big_null b);
id
----
(0 rows)
Time: 1.896 ms
[local]:5432 pg12@testdb=# select * from tbl3 where id not in (select b.id from t_big_null b);
id
----
(0 rows)
Time: 4653.525 ms (00:04.654)
[local]:5432 pg12@testdb=#
ExecScanSubPlan
/*
* ExecScanSubPlan: default case where we have to rescan subplan each time
* 默认情况下每次都不得不重新扫描subplan
*/
static Datum
ExecScanSubPlan(SubPlanState *node,
ExprContext *econtext,
bool *isNull)
{
SubPlan *subplan = node->subplan;//子计划
PlanState *planstate = node->planstate;//计划运行期状态
SubLinkType subLinkType = subplan->subLinkType;//子链接类型
MemoryContext oldcontext;//原内存上下文
TupleTableSlot *slot;//元组slot
Datum result;//结果指针
bool found = false; /* 如找到至少一个元组,则返回T;true if got at least one subplan tuple */
ListCell *pvar;//临时变量
ListCell *l;//临时变量
ArrayBuildStateAny *astate = NULL;//
/*
* MULTIEXPR subplans, when "executed", just return NULL; but first we
* mark the subplan's output parameters as needing recalculation. (This
* is a bit of a hack: it relies on the subplan appearing later in its
* targetlist than any of the referencing Params, so that all the Params
* have been evaluated before we re-mark them for the next evaluation
* cycle. But in general resjunk tlist items appear after non-resjunk
* ones, so this should be safe.) Unlike ExecReScanSetParamPlan, we do
* *not* set bits in the parent plan node's chgParam, because we don't
* want to cause a rescan of the parent.
*
* MULTIEXPR处理逻辑
*/
if (subLinkType == MULTIEXPR_SUBLINK)
{
EState *estate = node->parent->state;
foreach(l, subplan->setParam)
{
int paramid = lfirst_int(l);
ParamExecData *prm = &(estate->es_param_exec_vals[paramid]);
prm->execPlan = node;
}
*isNull = true;
return (Datum) 0;
}
/* Initialize ArrayBuildStateAny in caller's context, if needed */
//数组
if (subLinkType == ARRAY_SUBLINK)
astate = initArrayResultAny(subplan->firstColType,
CurrentMemoryContext, true);
/*
* We are probably in a short-lived expression-evaluation context. Switch
* to the per-query context for manipulating the child plan's chgParam,
* calling ExecProcNode on it, etc.
*/
//切换上下文
oldcontext = MemoryContextSwitchTo(econtext->ecxt_per_query_memory);
/*
* Set Params of this plan from parent plan correlation values. (Any
* calculation we have to do is done in the parent econtext, since the
* Param values don't need to have per-query lifetime.)
*/
//通过父计划相关值中设置子计划参数
Assert(list_length(subplan->parParam) == list_length(node->args));
forboth(l, subplan->parParam, pvar, node->args)
{
int paramid = lfirst_int(l);
ParamExecData *prm = &(econtext->ecxt_param_exec_vals[paramid]);
prm->value = ExecEvalExprSwitchContext((ExprState *) lfirst(pvar),
econtext,
&(prm->isnull));
planstate->chgParam = bms_add_member(planstate->chgParam, paramid);
}
/*
* Now that we've set up its parameters, we can reset the subplan.
*/
//执行ReScan
//Reset a plan node so that its output can be re-scanned.
ExecReScan(planstate);
/*
* For all sublink types except EXPR_SUBLINK and ARRAY_SUBLINK, the result
* is boolean as are the results of the combining operators. We combine
* results across tuples (if the subplan produces more than one) using OR
* semantics for ANY_SUBLINK or AND semantics for ALL_SUBLINK.
* (ROWCOMPARE_SUBLINK doesn't allow multiple tuples from the subplan.)
* NULL results from the combining operators are handled according to the
* usual SQL semantics for OR and AND. The result for no input tuples is
* FALSE for ANY_SUBLINK, TRUE for ALL_SUBLINK, NULL for
* ROWCOMPARE_SUBLINK.
* 除EXPR_SUBLINK和ARRAY_SUBLINK外的所有sublink,结果是布尔值(组合运算符的结果).
* PG通过跨元组(如子计划产生多个元组)合并结果,对于ANY_SUBLINK使用OR语义,ALL_SUBLINK则使用AND语义.
* (ROWCOMPARE_SUBLINK不允许子计划返回多个元组)
* 从组合操作符中返回的NULL遵循SQL中的OR和AND语义.
* 如没有输入元组,ANY_SUBLINK为FALSE,ALL_SUBLINK为TRUE,ROWCOMPARE_SUBLINK为NULL.
*
* For EXPR_SUBLINK we require the subplan to produce no more than one
* tuple, else an error is raised. If zero tuples are produced, we return
* NULL. Assuming we get a tuple, we just use its first column (there can
* be only one non-junk column in this case).
* 对于EXPR_SUBLINK,需要subplan产生不超过一个元组,否则报错.如果没有元组产生,返回NULL.
* 假定获取到一个元组,则使用第一个列(这种情况下只有一个non-junk列).
*
* For ARRAY_SUBLINK we allow the subplan to produce any number of tuples,
* and form an array of the first column's values. Note in particular
* that we produce a zero-element array if no tuples are produced (this is
* a change from pre-8.3 behavior of returning NULL).
* 对于ARRAY_SUBLINK,允许subplan产生任意数目的元组,使用第一个列值组成数组.
* 特别注意的是如没有元组产生则产生0个元素的数组(8.3以前是返回NULL).
*/
result = BoolGetDatum(subLinkType == ALL_SUBLINK);//ALL为T,否则为F
*isNull = false;
for (slot = ExecProcNode(planstate);
!TupIsNull(slot);
slot = ExecProcNode(planstate))//循环获取元组,直至没有元组为NULL(即已完成)
{
//元组描述符
TupleDesc tdesc = slot->tts_tupleDescriptor;
Datum rowresult;//结果
bool rownull;//是否为空?
int col;//列计数器
ListCell *plst;//临时变量
if (subLinkType == EXISTS_SUBLINK)//EXISTS
{
found = true;
result = BoolGetDatum(true);
break;
}
if (subLinkType == EXPR_SUBLINK)//EXPR表达式
{
/* cannot allow multiple input tuples for EXPR sublink */
if (found)
ereport(ERROR,
(errcode(ERRCODE_CARDINALITY_VIOLATION),
errmsg("more than one row returned by a subquery used as an expression")));
found = true;
/*
* We need to copy the subplan's tuple in case the result is of
* pass-by-ref type --- our return value will point into this
* copied tuple! Can't use the subplan's instance of the tuple
* since it won't still be valid after next ExecProcNode() call.
* node->curTuple keeps track of the copied tuple for eventual
* freeing.
*/
if (node->curTuple)
heap_freetuple(node->curTuple);
node->curTuple = ExecCopySlotHeapTuple(slot);
result = heap_getattr(node->curTuple, 1, tdesc, isNull);
/* keep scanning subplan to make sure there's only one tuple */
continue;
}
if (subLinkType == ARRAY_SUBLINK)//数组
{
Datum dvalue;
bool disnull;
found = true;
/* stash away current value */
Assert(subplan->firstColType == TupleDescAttr(tdesc, 0)->atttypid);
dvalue = slot_getattr(slot, 1, &disnull);
astate = accumArrayResultAny(astate, dvalue, disnull,
subplan->firstColType, oldcontext);
/* keep scanning subplan to collect all values */
continue;
}
/* cannot allow multiple input tuples for ROWCOMPARE sublink either */
if (subLinkType == ROWCOMPARE_SUBLINK && found)//行比较
ereport(ERROR,
(errcode(ERRCODE_CARDINALITY_VIOLATION),
errmsg("more than one row returned by a subquery used as an expression")));
found = true;//初始为T
/*
* For ALL, ANY, and ROWCOMPARE sublinks, load up the Params
* representing the columns of the sub-select, and then evaluate the
* combining expression.
* 对于ALL,ANY和ROWCOMPARE子链接,加载表示子查询列的Params,并解析组合表达式
*/
col = 1;//列从1计数
foreach(plst, subplan->paramIds)//循环遍历子查询参数
{
int paramid = lfirst_int(plst);
ParamExecData *prmdata;
prmdata = &(econtext->ecxt_param_exec_vals[paramid]);
Assert(prmdata->execPlan == NULL);
//获取参数值
prmdata->value = slot_getattr(slot, col, &(prmdata->isnull));
//下一个列
col++;
}
//解析表达式
rowresult = ExecEvalExprSwitchContext(node->testexpr, econtext,
&rownull);
if (subLinkType == ANY_SUBLINK)
{
//ANY : 使用OR语义组合
/* combine across rows per OR semantics */
if (rownull)
*isNull = true;
else if (DatumGetBool(rowresult))
{
result = BoolGetDatum(true);
*isNull = false;
break; /* needn't look at any more rows */
}
}
else if (subLinkType == ALL_SUBLINK)
{
//ALL : 使用AND语义
/* combine across rows per AND semantics */
if (rownull)
*isNull = true;
else if (!DatumGetBool(rowresult))
{
result = BoolGetDatum(false);
*isNull = false;
break; /* needn't look at any more rows */
}
}
else
{
/* must be ROWCOMPARE_SUBLINK */
//这里一定是ROWCOMPARE
result = rowresult;
*isNull = rownull;
}
}
MemoryContextSwitchTo(oldcontext);
if (subLinkType == ARRAY_SUBLINK)
{
/* We return the result in the caller's context */
//在调用者上下文中返回结果
result = makeArrayResultAny(astate, oldcontext, true);
}
else if (!found)
{
/*
* deal with empty subplan result. result/isNull were previously
* initialized correctly for all sublink types except EXPR and
* ROWCOMPARE; for those, return NULL.
* subplan没有结果返回,设置result&isNull值
*/
if (subLinkType == EXPR_SUBLINK ||
subLinkType == ROWCOMPARE_SUBLINK)
{
result = (Datum) 0;
*isNull = true;
}
}
//返回结果
return result;
}
三、跟踪分析
执行SQL：
[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，设置断点，观察到断点hit 1760次后就会退出，因此设置为忽略前1758次，只跟踪最后2次。
(gdb) info b
Num Type Disp Enb Address What
13 breakpoint keep y 0x0000000000721126 in ExecMaterial at nodeMaterial.c:150
breakpoint already hit 1760 times
ignore next 3360 hits
...
(gdb) b nodeSubplan.c:328
Breakpoint 17 at 0x7303b9: file nodeSubplan.c, line 328.
(gdb) del 16
(gdb) info b
Num Type Disp Enb Address What
17 breakpoint keep y 0x00000000007303b9 in ExecScanSubPlan at nodeSubplan.c:328
(gdb) ignore 17 1758
Will ignore next 1758 crossings of breakpoint 17.
(gdb) c
Continuing.
开始跟踪，这是第1759次，这时候从SubPlan获取的数据是id = 10000000
Breakpoint 17, ExecScanSubPlan (node=0x3069268, econtext=0x3068aa0, isNull=0x3068dbd)
at nodeSubplan.c:328
328 TupleDesc tdesc = slot->tts_tupleDescriptor;
(gdb) n
334 if (subLinkType == EXISTS_SUBLINK)
(gdb)
341 if (subLinkType == EXPR_SUBLINK)
(gdb)
367 if (subLinkType == ARRAY_SUBLINK)
(gdb)
383 if (subLinkType == ROWCOMPARE_SUBLINK && found)
(gdb)
388 found = true;
(gdb)
395 col = 1;
(gdb)
396 foreach(plst, subplan->paramIds)
(gdb)
398 int paramid = lfirst_int(plst);
(gdb)
401 prmdata = &(econtext->ecxt_param_exec_vals[paramid]);
(gdb)
402 Assert(prmdata->execPlan == NULL);
(gdb)
403 prmdata->value = slot_getattr(slot, col, &(prmdata->isnull));
(gdb) p *prmdata
$109 = {execPlan = 0x0, value = 9999999, isnull = false}
(gdb) n
404 col++;
(gdb) p *prmdata
$110 = {execPlan = 0x0, value = 10000000, isnull = false}
(gdb) n
396 foreach(plst, subplan->paramIds)
(gdb)
解析表达式
407 rowresult = ExecEvalExprSwitchContext(node->testexpr, econtext,
(gdb) step
ExecEvalExprSwitchContext (state=0x3069380, econtext=0x3068aa0, isNull=0x7ffd184750ef)
at ../../../src/include/executor/executor.h:306
306 oldContext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
(gdb) n
307 retDatum = state->evalfunc(state, econtext, isNull);
(gdb) step
ExecInterpExpr (state=0x3069380, econtext=0x3068aa0, isnull=0x7ffd184750ef)
at execExprInterp.c:404
404 if (unlikely(state == NULL))
(gdb) n
411 op = state->steps;
(gdb) p *state
$111 = {tag = {type = T_ExprState}, flags = 6 '\006', resnull = false, resvalue = 0,
resultslot = 0x0, steps = 0x3069418, evalfunc = 0x6e2d4d ,
expr = 0x30917a8, evalfunc_private = 0x6e2d4d , steps_len = 5,
steps_alloc = 16, parent = 0x3068988, ext_params = 0x0, innermost_caseval = 0x0,
innermost_casenull = 0x0, innermost_domainval = 0x0, innermost_domainnull = 0x0}
(gdb) n
412 resultslot = state->resultslot;
(gdb)
413 innerslot = econtext->ecxt_innertuple;
(gdb)
414 outerslot = econtext->ecxt_outertuple;
(gdb)
415 scanslot = econtext->ecxt_scantuple;
(gdb) p *innerslot
Cannot access memory at address 0x0
(gdb) p *outerslot
Cannot access memory at address 0x0
(gdb) n
418 EEO_DISPATCH();
(gdb) p *scanslot
$112 = {type = T_TupleTableSlot, tts_flags = 16, tts_nvalid = 1,
tts_ops = 0xc3e780 , tts_tupleDescriptor = 0x7fab449c99f0,
tts_values = 0x3068bd0, tts_isnull = 0x3068be0, tts_mcxt = 0x3067da0, tts_tid = {
ip_blkid = {bi_hi = 0, bi_lo = 0}, ip_posid = 2}, tts_tableOid = 40960}
(gdb) p *scanslot->tts_values
$113 = 1
(gdb) n
448 CheckOpSlotCompatibility(op, scanslot);
(gdb) n
450 slot_getsomeattrs(scanslot, op->d.fetch.last_var);
(gdb)
452 EEO_NEXT();
(gdb)
487 int attnum = op->d.var.attnum;
(gdb)
491 Assert(attnum >= 0 && attnum < scanslot->tts_nvalid);
(gdb)
492 *op->resvalue = scanslot->tts_values[attnum];
(gdb)
493 *op->resnull = scanslot->tts_isnull[attnum];
(gdb)
495 EEO_NEXT();
(gdb) p *op->resvalue
$114 = 1
(gdb) n
962 ExecEvalParamExec(state, op, econtext);
(gdb)
964 EEO_NEXT();
(gdb) p *op
$115 = {opcode = 7224136, resvalue = 0x30698b8, resnull = 0x30698c0, d = {fetch = {
last_var = 0, fixed = 23, known_desc = 0x0, kind = 0x0}, var = {attnum = 0,
vartype = 23}, wholerow = {var = 0x1700000000, first = false, slow = false,
tupdesc = 0x0, junkFilter = 0x0}, assign_var = {resultnum = 0, attnum = 23},
assign_tmp = {resultnum = 0}, constval = {value = 98784247808, isnull = false},
func = {finfo = 0x1700000000, fcinfo_data = 0x0, fn_addr = 0x0, nargs = 0},
boolexpr = {anynull = 0x1700000000, jumpdone = 0}, qualexpr = {jumpdone = 0}, jump = {
jumpdone = 0}, nulltest_row = {argdesc = 0x1700000000}, param = {paramid = 0,
paramtype = 23}, cparam = {paramfunc = 0x1700000000, paramarg = 0x0, paramid = 0,
paramtype = 0}, casetest = {value = 0x1700000000, isnull = 0x0}, make_readonly = {
value = 0x1700000000, isnull = 0x0}, iocoerce = {finfo_out = 0x1700000000,
fcinfo_data_out = 0x0, finfo_in = 0x0, fcinfo_data_in = 0x0}, sqlvaluefunction = {
svf = 0x1700000000}, nextvalueexpr = {seqid = 0, seqtypid = 23}, arrayexpr = {
elemvalues = 0x1700000000, elemnulls = 0x0, nelems = 0, elemtype = 0,
elemlength = 0, elembyval = false, elemalign = 0 '\000', multidims = false},
arraycoerce = {elemexprstate = 0x1700000000, resultelemtype = 0, amstate = 0x0},
row = {tupdesc = 0x1700000000, elemvalues = 0x0, elemnulls = 0x0}, rowcompare_step = {
finfo = 0x1700000000, fcinfo_data = 0x0, fn_addr = 0x0, jumpnull = 0,
jumpdone = 0}, rowcompare_final = {rctype = 0}, minmax = {values = 0x1700000000,
nulls = 0x0, nelems = 0, op = IS_GREATEST, finfo = 0x0, fcinfo_data = 0x0},
fieldselect = {fieldnum = 0, resulttype = 23, argdesc = 0x0}, fieldstore = {
fstore = 0x1700000000, argdesc = 0x0, values = 0x0, nulls = 0x0, ncolumns = 0},
sbsref_subscript = {state = 0x1700000000, off = 0, isupper = false, jumpdone = 0},
sbsref = {state = 0x1700000000}, domaincheck = {
constraintname = 0x1700000000 ,
checkvalue = 0x0, checknull = 0x0, resulttype = 0}, convert_rowtype = {
convert = 0x1700000000, indesc = 0x0, outdesc = 0x0, map = 0x0,
initialized = false}, scalararrayop = {element_type = 0, useOr = 23, typlen = 0,
typbyval = false, typalign = 0 '\000', finfo = 0x0, fcinfo_data = 0x0,
fn_addr = 0x0}, xmlexpr = {xexpr = 0x1700000000, named_argvalue = 0x0,
named_argnull = 0x0, argvalue = 0x0, argnull = 0x0}, aggref = {
astate = 0x1700000000}, grouping_func = {parent = 0x1700000000, clauses = 0x0},
window_func = {wfstate = 0x1700000000}, subplan = {sstate = 0x1700000000},
alternative_subplan = {asstate = 0x1700000000}, agg_deserialize = {
aggstate = 0x1700000000, fcinfo_data = 0x0, jumpnull = 0},
agg_strict_input_check = {args = 0x1700000000, nulls = 0x0, nargs = 0, jumpnull = 0},
agg_init_trans = {aggstate = 0x1700000000, pertrans = 0x0, aggcontext = 0x0,
setno = 0, transno = 0, setoff = 0, jumpnull = 0}, agg_strict_trans_check = {
aggstate = 0x1700000000, setno = 0, transno = 0, setoff = 0, jumpnull = 0},
agg_trans = {aggstate = 0x1700000000, pertrans = 0x0, aggcontext = 0x0, setno = 0,
transno = 0, setoff = 0}}}
(gdb) p *state
$116 = {tag = {type = T_ExprState}, flags = 6 '\006', resnull = false, resvalue = 0,
resultslot = 0x0, steps = 0x3069418, evalfunc = 0x6e2d4d ,
expr = 0x30917a8, evalfunc_private = 0x6e2d4d , steps_len = 5,
steps_alloc = 16, parent = 0x3068988, ext_params = 0x0, innermost_caseval = 0x0,
innermost_casenull = 0x0, innermost_domainval = 0x0, innermost_domainnull = 0x0}
(gdb) n
634 FunctionCallInfo fcinfo = op->d.func.fcinfo_data;
(gdb)
635 NullableDatum *args = fcinfo->args;
(gdb) p *fcinfo
$117 = {flinfo = 0x3069830, context = 0x0, resultinfo = 0x0, fncollation = 0,
isnull = false, nargs = 2, args = 0x30698a8}
(gdb) p *fcinfo->args
$118 = {value = 1, isnull = false}
(gdb) n
640 for (argno = 0; argno < op->d.func.nargs; argno++)
(gdb) p op->d.func.nargs
$119 = 2
(gdb) p *op
$120 = {opcode = 7222440, resvalue = 0x3069388, resnull = 0x3069385, d = {fetch = {
last_var = 50763824, fixed = false, known_desc = 0x3069888,
kind = 0x96c2b2 }, var = {attnum = 50763824, vartype = 0}, wholerow = {
var = 0x3069830, first = 136, slow = 152, tupdesc = 0x96c2b2 ,
junkFilter = 0x2}, assign_var = {resultnum = 50763824, attnum = 0}, assign_tmp = {
resultnum = 50763824}, constval = {value = 50763824, isnull = 136}, func = {
finfo = 0x3069830, fcinfo_data = 0x3069888, fn_addr = 0x96c2b2 ,
nargs = 2}, boolexpr = {anynull = 0x3069830, jumpdone = 50763912}, qualexpr = {
jumpdone = 50763824}, jump = {jumpdone = 50763824}, nulltest_row = {
argdesc = 0x3069830}, param = {paramid = 50763824, paramtype = 0}, cparam = {
paramfunc = 0x3069830, paramarg = 0x3069888, paramid = 9880242, paramtype = 0},
casetest = {value = 0x3069830, isnull = 0x3069888}, make_readonly = {
value = 0x3069830, isnull = 0x3069888}, iocoerce = {finfo_out = 0x3069830,
fcinfo_data_out = 0x3069888, finfo_in = 0x96c2b2 , fcinfo_data_in = 0x2},
sqlvaluefunction = {svf = 0x3069830}, nextvalueexpr = {seqid = 50763824,
seqtypid = 0}, arrayexpr = {elemvalues = 0x3069830, elemnulls = 0x3069888,
nelems = 9880242, elemtype = 0, elemlength = 2, elembyval = false,
elemalign = 0 '\000', multidims = false}, arraycoerce = {elemexprstate = 0x3069830,
resultelemtype = 50763912, amstate = 0x96c2b2 }, row = {
tupdesc = 0x3069830, elemvalues = 0x3069888, elemnulls = 0x96c2b2 },
rowcompare_step = {finfo = 0x3069830, fcinfo_data = 0x3069888,
fn_addr = 0x96c2b2 , jumpnull = 2, jumpdone = 0}, rowcompare_final = {
rctype = 50763824}, minmax = {values = 0x3069830, nulls = 0x3069888,
nelems = 9880242, op = IS_GREATEST, finfo = 0x2, fcinfo_data = 0x0}, fieldselect = {
fieldnum = -26576, resulttype = 0, argdesc = 0x3069888}, fieldstore = {
fstore = 0x3069830, argdesc = 0x3069888, values = 0x96c2b2 , nulls = 0x2,
ncolumns = 0}, sbsref_subscript = {state = 0x3069830, off = 50763912,
isupper = false, jumpdone = 9880242}, sbsref = {state = 0x3069830}, domaincheck = {
constraintname = 0x3069830 "\262\302\226", checkvalue = 0x3069888,
checknull = 0x96c2b2 , resulttype = 2}, convert_rowtype = {
convert = 0x3069830, indesc = 0x3069888, outdesc = 0x96c2b2 , map = 0x2,
initialized = false}, scalararrayop = {element_type = 50763824, useOr = false,
typlen = 0, typbyval = 136, typalign = -104 '\230', finfo = 0x96c2b2 ,
fcinfo_data = 0x2, fn_addr = 0x0}, xmlexpr = {xexpr = 0x3069830,
named_argvalue = 0x3069888, named_argnull = 0x96c2b2 , argvalue = 0x2,
argnull = 0x0}, aggref = {astate = 0x3069830}, grouping_func = {parent = 0x3069830,
clauses = 0x3069888}, window_func = {wfstate = 0x3069830}, subplan = {
sstate = 0x3069830}, alternative_subplan = {asstate = 0x3069830},
agg_deserialize = {aggstate = 0x3069830, fcinfo_data = 0x3069888,
jumpnull = 9880242}, agg_strict_input_check = {args = 0x3069830, nulls = 0x3069888,
nargs = 9880242, jumpnull = 0}, agg_init_trans = {aggstate = 0x3069830,
pertrans = 0x3069888, aggcontext = 0x96c2b2 , setno = 2, transno = 0,
setoff = 0, jumpnull = 0}, agg_strict_trans_check = {aggstate = 0x3069830,
setno = 50763912, transno = 0, setoff = 9880242, jumpnull = 0}, agg_trans = {
aggstate = 0x3069830, pertrans = 0x3069888, aggcontext = 0x96c2b2 ,
setno = 2, transno = 0, setoff = 0}}}
(gdb) p op->d->func
$121 = {finfo = 0x3069830, fcinfo_data = 0x3069888, fn_addr = 0x96c2b2 ,
nargs = 2}
(gdb) p op->d->func->finfo
$122 = (FmgrInfo *) 0x3069830
(gdb) p *op->d->func->finfo
$123 = {fn_addr = 0x96c2b2 , fn_oid = 65, fn_nargs = 2, fn_strict = true,
fn_retset = false, fn_stats = 2 '\002', fn_extra = 0x0, fn_mcxt = 0x3067da0,
fn_expr = 0x30917a8}
(gdb) p *op->d->func->fcinfo_data
$124 = {flinfo = 0x3069830, context = 0x0, resultinfo = 0x0, fncollation = 0,
isnull = false, nargs = 2, args = 0x30698a8}
(gdb) p *op->d->func->fcinfo_data->flinfo
$125 = {fn_addr = 0x96c2b2 , fn_oid = 65, fn_nargs = 2, fn_strict = true,
fn_retset = false, fn_stats = 2 '\002', fn_extra = 0x0, fn_mcxt = 0x3067da0,
fn_expr = 0x30917a8}
(gdb) p *op->d->func->fcinfo_data->args
$126 = {value = 1, isnull = false}
(gdb) n
642 if (args[argno].isnull)
(gdb)
640 for (argno = 0; argno < op->d.func.nargs; argno++)
(gdb)
642 if (args[argno].isnull)
(gdb)
640 for (argno = 0; argno < op->d.func.nargs; argno++)
(gdb)
648 fcinfo->isnull = false;
(gdb) p *args
$127 = {value = 1, isnull = false}
(gdb) n
649 d = op->d.func.fn_addr(fcinfo);
(gdb)
650 *op->resvalue = d;
(gdb) p d
$128 = 0
(gdb) n
651 *op->resnull = fcinfo->isnull;
(gdb)
654 EEO_NEXT();
(gdb)
425 goto out;
(gdb) n
1747 *isnull = state->resnull;
(gdb)
1748 return state->resvalue;
(gdb) p *state
$129 = {tag = {type = T_ExprState}, flags = 6 '\006', resnull = false, resvalue = 0,
resultslot = 0x0, steps = 0x3069418, evalfunc = 0x6e2d4d ,
expr = 0x30917a8, evalfunc_private = 0x6e2d4d , steps_len = 5,
steps_alloc = 16, parent = 0x3068988, ext_params = 0x0, innermost_caseval = 0x0,
innermost_casenull = 0x0, innermost_domainval = 0x0, innermost_domainnull = 0x0}
(gdb) n
1749 }
(gdb)
ExecEvalExprSwitchContext (state=0x3069380, econtext=0x3068aa0, isNull=0x7ffd184750ef)
at ../../../src/include/executor/executor.h:308
308 MemoryContextSwitchTo(oldContext);
(gdb)
309 return retDatum;
(gdb) p retDatum
$130 = 0
(gdb) n
310 }
(gdb)
这是第1760次调用
ExecScanSubPlan (node=0x3069268, econtext=0x3068aa0, isNull=0x3068dbd)
at nodeSubplan.c:410
410 if (subLinkType == ANY_SUBLINK)
(gdb)
413 if (rownull)
(gdb)
415 else if (DatumGetBool(rowresult))
(gdb) p rowresult
$131 = 0
(gdb) n
326 slot = ExecProcNode(planstate))
(gdb)
324 for (slot = ExecProcNode(planstate);
(gdb)
325 !TupIsNull(slot);
(gdb)
Breakpoint 17, ExecScanSubPlan (node=0x3069268, econtext=0x3068aa0, isNull=0x3068dbd)
at nodeSubplan.c:328
328 TupleDesc tdesc = slot->tts_tupleDescriptor;
(gdb)
334 if (subLinkType == EXISTS_SUBLINK)
(gdb)
341 if (subLinkType == EXPR_SUBLINK)
(gdb)
367 if (subLinkType == ARRAY_SUBLINK)
(gdb)
383 if (subLinkType == ROWCOMPARE_SUBLINK && found)
(gdb)
388 found = true;
(gdb)
395 col = 1;
(gdb) p *slot->tts_values
$132 = 10000000 --> 上一次的数据
(gdb) n
396 foreach(plst, subplan->paramIds)
(gdb)
398 int paramid = lfirst_int(plst);
(gdb)
401 prmdata = &(econtext->ecxt_param_exec_vals[paramid]);
(gdb)
402 Assert(prmdata->execPlan == NULL);
(gdb) p *prmdata
$133 = {execPlan = 0x0, value = 10000000, isnull = false}
(gdb) n
403 prmdata->value = slot_getattr(slot, col, &(prmdata->isnull));
(gdb)
404 col++;
(gdb) p *prmdata
$134 = {execPlan = 0x0, value = 1, isnull = false} --> 本次数据，值为1
(gdb) info b
Num Type Disp Enb Address What
17 breakpoint keep y 0x00000000007303b9 in ExecScanSubPlan at nodeSubplan.c:328
breakpoint already hit 1760 times
(gdb) n
396 foreach(plst, subplan->paramIds)
(gdb)
407 rowresult = ExecEvalExprSwitchContext(node->testexpr, econtext,
(gdb)
410 if (subLinkType == ANY_SUBLINK)
(gdb)
413 if (rownull)
(gdb)
415 else if (DatumGetBool(rowresult))
(gdb)
417 result = BoolGetDatum(true);
(gdb)
418 *isNull = false;
(gdb)
419 break; /* needn't look at any more rows */
(gdb)
442 MemoryContextSwitchTo(oldcontext);
(gdb)
444 if (subLinkType == ARRAY_SUBLINK)
(gdb)
449 else if (!found)
(gdb)
464 return result;
(gdb)
(gdb) p result
$135 = 1 --> 满足条件
DONE
四、参考资料
N/A
