本节介绍了ExecPrepareTupleRouting->ExecFindPartition->FormPartitionKeyDatum函数，该函数获取Tuple的分区键值。
一、数据结构
ModifyTable
通过插入、更新或删除，将子计划生成的行应用到结果表。
/* ----------------
* ModifyTable node -
* Apply rows produced by subplan(s) to result table(s),
* by inserting, updating, or deleting.
* 通过插入、更新或删除，将子计划生成的行应用到结果表。
*
* If the originally named target table is a partitioned table, both
* nominalRelation and rootRelation contain the RT index of the partition
* root, which is not otherwise mentioned in the plan. Otherwise rootRelation
* is zero. However, nominalRelation will always be set, as it's the rel that
* EXPLAIN should claim is the INSERT/UPDATE/DELETE target.
* 如果最初命名的目标表是分区表，则nominalRelation和rootRelation都包含分区根的RT索引，计划中没有另外提到这个索引。
* 否则，根关系为零。但是，总是会设置名义关系，nominalRelation因为EXPLAIN应该声明的rel是INSERT/UPDATE/DELETE目标关系。
*
* Note that rowMarks and epqParam are presumed to be valid for all the
* subplan(s); they can't contain any info that varies across subplans.
* 注意，rowMarks和epqParam被假定对所有子计划有效;
* 它们不能包含任何在子计划中变化的信息。
* ----------------
*/
typedef struct ModifyTable
{
Plan plan;
CmdType operation; /* 操作类型;INSERT, UPDATE, or DELETE */
bool canSetTag; /* 是否需要设置tag?do we set the command tag/es_processed? */
Index nominalRelation; /* 用于EXPLAIN的父RT索引;Parent RT index for use of EXPLAIN */
Index rootRelation; /* 根Root RT索引(如目标为分区表);Root RT index, if target is partitioned */
bool partColsUpdated; /* 更新了层次结构中的分区关键字;some part key in hierarchy updated */
List *resultRelations; /* RT索引的整型链表;integer list of RT indexes */
int resultRelIndex; /* 计划链表中第一个resultRel的索引;index of first resultRel in plan's list */
int rootResultRelIndex; /* 分区表根索引;index of the partitioned table root */
List *plans; /* 生成源数据的计划链表;plan(s) producing source data */
List *withCheckOptionLists; /* 每一个目标表均具备的WCO链表;per-target-table WCO lists */
List *returningLists; /* 每一个目标表均具备的RETURNING链表;per-target-table RETURNING tlists */
List *fdwPrivLists; /* 每一个目标表的FDW私有数据链表;per-target-table FDW private data lists */
Bitmapset *fdwDirectModifyPlans; /* FDW DM计划索引位图;indices of FDW DM plans */
List *rowMarks; /* rowMarks链表;PlanRowMarks (non-locking only) */
int epqParam; /* EvalPlanQual再解析使用的参数ID;ID of Param for EvalPlanQual re-eval */
OnConflictAction onConflictAction; /* ON CONFLICT action */
List *arbiterIndexes; /* 冲突仲裁器索引表;List of ON CONFLICT arbiter index OIDs */
List *onConflictSet; /* SET for INSERT ON CONFLICT DO UPDATE */
Node *onConflictWhere; /* WHERE for ON CONFLICT UPDATE */
Index exclRelRTI; /* RTI of the EXCLUDED pseudo relation */
List *exclRelTlist; /* 已排除伪关系的投影列链表;tlist of the EXCLUDED pseudo relation */
} ModifyTable;
ResultRelInfo
ResultRelInfo结构体
每当更新一个现有的关系时，我们必须更新关系上的索引，也许还需要触发触发器。ResultRelInfo保存关于结果关系所需的所有信息，包括索引。
/*
* ResultRelInfo
* ResultRelInfo结构体
*
* Whenever we update an existing relation, we have to update indexes on the
* relation, and perhaps also fire triggers. ResultRelInfo holds all the
* information needed about a result relation, including indexes.
* 每当更新一个现有的关系时，我们必须更新关系上的索引，也许还需要触发触发器。
* ResultRelInfo保存关于结果关系所需的所有信息，包括索引。
*
* Normally, a ResultRelInfo refers to a table that is in the query's
* range table; then ri_RangeTableIndex is the RT index and ri_RelationDesc
* is just a copy of the relevant es_relations[] entry. But sometimes,
* in ResultRelInfos used only for triggers, ri_RangeTableIndex is zero
* and ri_RelationDesc is a separately-opened relcache pointer that needs
* to be separately closed. See ExecGetTriggerResultRel.
* 通常，ResultRelInfo是指查询范围表中的表;
* ri_RangeTableIndex是RT索引，而ri_RelationDesc只是相关es_relations[]条目的副本。
* 但有时，在只用于触发器的ResultRelInfos中，ri_RangeTableIndex为零(NULL)，
* 而ri_RelationDesc是一个需要单独关闭单独打开的relcache指针。
* 具体可参考ExecGetTriggerResultRel结构体。
*/
typedef struct ResultRelInfo
{
NodeTag type;
/* result relation's range table index, or 0 if not in range table */
//RTE索引
Index ri_RangeTableIndex;
/* relation descriptor for result relation */
//结果/目标relation的描述符
Relation ri_RelationDesc;
/* # of indices existing on result relation */
//目标关系中索引数目
int ri_NumIndices;
/* array of relation descriptors for indices */
//索引的关系描述符数组(索引视为一个relation)
RelationPtr ri_IndexRelationDescs;
/* array of key/attr info for indices */
//索引的键/属性数组
IndexInfo **ri_IndexRelationInfo;
/* triggers to be fired, if any */
//触发的索引
TriggerDesc *ri_TrigDesc;
/* cached lookup info for trigger functions */
//触发器函数(缓存)
FmgrInfo *ri_TrigFunctions;
/* array of trigger WHEN expr states */
//WHEN表达式状态的触发器数组
ExprState **ri_TrigWhenExprs;
/* optional runtime measurements for triggers */
//可选的触发器运行期度量器
Instrumentation *ri_TrigInstrument;
/* FDW callback functions, if foreign table */
//FDW回调函数
struct FdwRoutine *ri_FdwRoutine;
/* available to save private state of FDW */
//可用于存储FDW的私有状态
void *ri_FdwState;
/* true when modifying foreign table directly */
//直接更新FDW时为T
bool ri_usesFdwDirectModify;
/* list of WithCheckOption's to be checked */
//WithCheckOption链表
List *ri_WithCheckOptions;
/* list of WithCheckOption expr states */
//WithCheckOption表达式链表
List *ri_WithCheckOptionExprs;
/* array of constraint-checking expr states */
//约束检查表达式状态数组
ExprState **ri_ConstraintExprs;
/* for removing junk attributes from tuples */
//用于从元组中删除junk属性
JunkFilter *ri_junkFilter;
/* list of RETURNING expressions */
//RETURNING表达式链表
List *ri_returningList;
/* for computing a RETURNING list */
//用于计算RETURNING链表
ProjectionInfo *ri_projectReturning;
/* list of arbiter indexes to use to check conflicts */
//用于检查冲突的仲裁器索引的列表
List *ri_onConflictArbiterIndexes;
/* ON CONFLICT evaluation state */
//ON CONFLICT解析状态
OnConflictSetState *ri_onConflict;
/* partition check expression */
//分区检查表达式链表
List *ri_PartitionCheck;
/* partition check expression state */
//分区检查表达式状态
ExprState *ri_PartitionCheckExpr;
/* relation descriptor for root partitioned table */
//分区root根表描述符
Relation ri_PartitionRoot;
/* Additional information specific to partition tuple routing */
//额外的分区元组路由信息
struct PartitionRoutingInfo *ri_PartitionInfo;
} ResultRelInfo;
PartitionRoutingInfo
PartitionRoutingInfo结构体
分区路由信息,用于将元组路由到表分区的结果关系信息。
/*
* PartitionRoutingInfo
* PartitionRoutingInfo - 分区路由信息
*
* Additional result relation information specific to routing tuples to a
* table partition.
* 用于将元组路由到表分区的结果关系信息。
*/
typedef struct PartitionRoutingInfo
{
/*
* Map for converting tuples in root partitioned table format into
* partition format, or NULL if no conversion is required.
* 映射，用于将根分区表格式的元组转换为分区格式，如果不需要转换，则转换为NULL。
*/
TupleConversionMap *pi_RootToPartitionMap;
/*
* Map for converting tuples in partition format into the root partitioned
* table format, or NULL if no conversion is required.
* 映射，用于将分区格式的元组转换为根分区表格式，如果不需要转换，则转换为NULL。
*/
TupleConversionMap *pi_PartitionToRootMap;
/*
* Slot to store tuples in partition format, or NULL when no translation
* is required between root and partition.
* 以分区格式存储元组的slot.在根分区和分区之间不需要转换时为NULL。
*/
TupleTableSlot *pi_PartitionTupleSlot;
} PartitionRoutingInfo;
TupleConversionMap
TupleConversionMap结构体,用于存储元组转换映射信息.
typedef struct TupleConversionMap
{
TupleDesc indesc; /* 源行类型的描述符;tupdesc for source rowtype */
TupleDesc outdesc; /* 结果行类型的描述符;tupdesc for result rowtype */
AttrNumber *attrMap; /* 输入字段的索引信息,0表示NULL;indexes of input fields, or 0 for null */
Datum *invalues; /* 析构源数据的工作空间;workspace for deconstructing source */
bool *inisnull; //是否为NULL标记数组
Datum *outvalues; /* 构造结果的工作空间;workspace for constructing result */
bool *outisnull; //null标记
} TupleConversionMap;
二、源码解读
FormPartitionKeyDatum函数获取Tuple的分区键值,返回键值values[]数组和是否为null标记isnull[]数组.
/* ----------------
* FormPartitionKeyDatum
* Construct values[] and isnull[] arrays for the partition key
* of a tuple.
* 构造values[]数组和isnull[]数组
*
* pd Partition dispatch object of the partitioned table
* pd 分区表的分区分发器(dispatch)对象
*
* slot Heap tuple from which to extract partition key
* slot 从其中提前分区键的heap tuple
*
* estate executor state for evaluating any partition key
* expressions (must be non-NULL)
* estate 解析分区键表达式(必须非NULL)的执行器状态
*
* values Array of partition key Datums (output area)
* 分区键Datums数组(输出参数)
* isnull Array of is-null indicators (output area)
* is-null标记数组(输出参数)
*
* the ecxt_scantuple slot of estate's per-tuple expr context must point to
* the heap tuple passed in.
* estate的per-tuple上下文的ecxt_scantuple必须指向传入的heap tuple
* ----------------
*/
static void
FormPartitionKeyDatum(PartitionDispatch pd,
TupleTableSlot *slot,
EState *estate,
Datum *values,
bool *isnull)
{
ListCell *partexpr_item;
int i;
if (pd->key->partexprs != NIL && pd->keystate == NIL)
{
/* Check caller has set up context correctly */
//检查调用者是否已正确配置内存上下文
Assert(estate != NULL &&
GetPerTupleExprContext(estate)->ecxt_scantuple == slot);
/* First time through, set up expression evaluation state */
//第一次进入,配置表达式解析器状态
pd->keystate = ExecPrepareExprList(pd->key->partexprs, estate);
}
partexpr_item = list_head(pd->keystate);//获取分区键表达式状态
for (i = 0; i < pd->key->partnatts; i++)//循环遍历分区键
{
AttrNumber keycol = pd->key->partattrs[i];//分区键属性编号
Datum datum;// typedef uintptr_t Datum;sizeof(Datum) == sizeof(void *) == 4 or 8
bool isNull;//是否null
if (keycol != 0)//编号不为0
{
/* Plain column; get the value directly from the heap tuple */
//扁平列,直接从堆元组中提取值
datum = slot_getattr(slot, keycol, &isNull);
}
else
{
/* Expression; need to evaluate it */
//表达式,需要解析
if (partexpr_item == NULL)//分区键表达式状态为NULL,报错
elog(ERROR, "wrong number of partition key expressions");
//获取表达式值
datum = ExecEvalExprSwitchContext((ExprState *) lfirst(partexpr_item),
GetPerTupleExprContext(estate),
&isNull);
//切换至下一个
partexpr_item = lnext(partexpr_item);
}
values[i] = datum;//赋值
isnull[i] = isNull;
}
if (partexpr_item != NULL)//参数设置有误?报错
elog(ERROR, "wrong number of partition key expressions");
}
/*
* slot_getattr - fetch one attribute of the slot's contents.
* slot_getattr - 提取slot中的某个属性值
*/
static inline Datum
slot_getattr(TupleTableSlot *slot, int attnum,
bool *isnull)
{
AssertArg(attnum > 0);
if (attnum > slot->tts_nvalid)
slot_getsomeattrs(slot, attnum);
*isnull = slot->tts_isnull[attnum - 1];
return slot->tts_values[attnum - 1];
}
/*
* This function forces the entries of the slot's Datum/isnull arrays to be
* valid at least up through the attnum'th entry.
* 这个函数强制slot的Datum/isnull数组的条目至少在attnum的第一个条目上是有效的。
*/
static inline void
slot_getsomeattrs(TupleTableSlot *slot, int attnum)
{
if (slot->tts_nvalid < attnum)
slot_getsomeattrs_int(slot, attnum);
}
/*
* slot_getsomeattrs_int - workhorse for slot_getsomeattrs()
* slot_getsomeattrs_int - slot_getsomeattrs()函数的实际实现
*/
void
slot_getsomeattrs_int(TupleTableSlot *slot, int attnum)
{
/* Check for caller errors */
//检查调用者输入参数是否有误
Assert(slot->tts_nvalid < attnum); /* slot_getsomeattr checked */
Assert(attnum > 0);
//attnum参数判断
if (unlikely(attnum > slot->tts_tupleDescriptor->natts))
elog(ERROR, "invalid attribute number %d", attnum);
/* Fetch as many attributes as possible from the underlying tuple. */
//从元组中获取尽可能多的属性。
slot->tts_ops->getsomeattrs(slot, attnum);
/*
* If the underlying tuple doesn't have enough attributes, tuple descriptor
* must have the missing attributes.
* 如果底层元组没有足够的属性，那么元组描述符必须具有缺少的属性。
*/
if (unlikely(slot->tts_nvalid < attnum))
{
slot_getmissingattrs(slot, slot->tts_nvalid, attnum);
slot->tts_nvalid = attnum;
}
}
三、跟踪分析
测试脚本如下
-- Hash Partition
drop table if exists t_hash_partition;
create table t_hash_partition (c1 int not null,c2 varchar(40),c3 varchar(40)) partition by hash(c1);
create table t_hash_partition_1 partition of t_hash_partition for values with (modulus 6,remainder 0);
create table t_hash_partition_2 partition of t_hash_partition for values with (modulus 6,remainder 1);
create table t_hash_partition_3 partition of t_hash_partition for values with (modulus 6,remainder 2);
create table t_hash_partition_4 partition of t_hash_partition for values with (modulus 6,remainder 3);
create table t_hash_partition_5 partition of t_hash_partition for values with (modulus 6,remainder 4);
create table t_hash_partition_6 partition of t_hash_partition for values with (modulus 6,remainder 5);
insert into t_hash_partition(c1,c2,c3) VALUES(20,'HASH0','HAHS0');
启动gdb,设置断点
(gdb) b FormPartitionKeyDatum
Breakpoint 5 at 0x6e30d2: file execPartition.c, line 1087.
(gdb) b slot_getattr
Breakpoint 6 at 0x489d9b: file heaptuple.c, line 1510.
(gdb) c
Continuing.
Breakpoint 5, FormPartitionKeyDatum (pd=0x2e1bfa0, slot=0x2e1b8a0, estate=0x2e1aeb8, values=0x7fff4e2407a0,
isnull=0x7fff4e240780) at execPartition.c:1087
1087 if (pd->key->partexprs != NIL && pd->keystate == NIL)
循环,根据分区键获取相应的键值
1087 if (pd->key->partexprs != NIL && pd->keystate == NIL)
(gdb) n
1097 partexpr_item = list_head(pd->keystate);
(gdb)
1098 for (i = 0; i < pd->key->partnatts; i++)
(gdb)
1100 AttrNumber keycol = pd->key->partattrs[i];
(gdb)
1104 if (keycol != 0)
(gdb)
1107 datum = slot_getattr(slot, keycol, &isNull);
进入函数slot_getattr
(gdb) step
Breakpoint 6, slot_getattr (slot=0x2e1b8a0, attnum=1, isnull=0x7fff4e240735) at heaptuple.c:1510
1510 HeapTuple tuple = slot->tts_tuple;
获取结果,分区键值为20
...
(gdb) p *isnull
$31 = false
(gdb) p slot->tts_values[attnum - 1]
$32 = 20
返回到FormPartitionKeyDatum函数中
(gdb) n
1593 }
(gdb)
FormPartitionKeyDatum (pd=0x2e1bfa0, slot=0x2e1b8a0, estate=0x2e1aeb8, values=0x7fff4e2407a0, isnull=0x7fff4e240780)
at execPartition.c:1119
1119 values[i] = datum;
完成调用
1119 values[i] = datum;
(gdb) n
1120 isnull[i] = isNull;
(gdb)
1098 for (i = 0; i < pd->key->partnatts; i++)
(gdb)
1123 if (partexpr_item != NULL)
(gdb)
1125 }
(gdb)
ExecFindPartition (resultRelInfo=0x2e1b108, pd=0x2e1c5b8, slot=0x2e1b8a0, estate=0x2e1aeb8) at execPartition.c:282
282 if (partdesc->nparts == 0)
DONE!
四、参考资料
PG 11.1 Source Code.
注: doxygen上的源代码与PG 11.1源代码并不一致,本节基于11.1进行分析.