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#yyds干货盘点#GreenPlum7聚合

悄然丝语 2022-03-19 阅读 52

聚合的执行需要状态描述信息,由AggState结构体管理。该结构体如下:

typedef struct AggState
{
ScanState ss; /* its first field is NodeTag */
List *aggs; /* all Aggref nodes in targetlist & quals */
int numaggs; /* length of list (could be zero!) */
int numtrans; /* number of pertrans items */
AggStrategy aggstrategy; /* strategy mode */
AggSplit aggsplit; /* agg-splitting mode, see nodes.h */
AggStatePerPhase phase; /* pointer to current phase data */
int numphases; /* number of phases (including phase 0) */
int current_phase; /* current phase number */
AggStatePerAgg peragg; /* per-Aggref information */
AggStatePerTrans pertrans; /* per-Trans state information */
ExprContext *hashcontext; /* econtexts for long-lived data (hashtable) */
ExprContext **aggcontexts; /* econtexts for long-lived data (per GS) */
ExprContext *tmpcontext; /* econtext for input expressions */
#define FIELDNO_AGGSTATE_CURAGGCONTEXT 14
ExprContext *curaggcontext; /* currently active aggcontext */
AggStatePerAgg curperagg; /* currently active aggregate, if any */
#define FIELDNO_AGGSTATE_CURPERTRANS 16
AggStatePerTrans curpertrans; /* currently active trans state, if any */
bool input_done; /* indicates end of input */
bool agg_done; /* indicates completion of Agg scan */
int projected_set; /* The last projected grouping set */
#define FIELDNO_AGGSTATE_CURRENT_SET 20
int current_set; /* The current grouping set being evaluated */
Bitmapset *grouped_cols; /* grouped cols in current projection */
List *all_grouped_cols; /* list of all grouped cols in DESC order */
/* These fields are for grouping set phase data */
int maxsets; /* The max number of sets in any phase */
AggStatePerPhase phases; /* array of all phases */
Tuplesortstate *sort_in; /* sorted input to phases > 1 */
Tuplesortstate *sort_out; /* input is copied here for next phase */
TupleTableSlot *sort_slot; /* slot for sort results */
/* these fields are used in AGG_PLAIN and AGG_SORTED modes: */
AggStatePerGroup *pergroups; /* grouping set indexed array of per-group
* pointers */
HeapTuple grp_firstTuple; /* copy of first tuple of current group */
/* these fields are used in AGG_HASHED and AGG_MIXED modes: */
bool table_filled; /* hash table filled yet? */
int num_hashes;
MemoryContext hash_metacxt; /* memory for hash table itself */
struct HashTapeInfo *hash_tapeinfo; /* metadata for spill tapes */
struct HashAggSpill *hash_spills; /* HashAggSpill for each grouping set,
exists only during first pass */
TupleTableSlot *hash_spill_slot; /* slot for reading from spill files */
List *hash_batches; /* hash batches remaining to be processed */
bool hash_ever_spilled; /* ever spilled during this execution? */
bool hash_spill_mode; /* we hit a limit during the current batch
and we must not create new groups */
Size hash_mem_limit; /* limit before spilling hash table */
uint64 hash_ngroups_limit; /* limit before spilling hash table */
int hash_planned_partitions; /* number of partitions planned
for first pass */
double hashentrysize; /* estimate revised during execution */
Size hash_mem_peak; /* peak hash table memory usage */
uint64 hash_ngroups_current; /* number of groups currently in
memory in all hash tables */
uint64 hash_disk_used; /* kB of disk space used */
int hash_batches_used; /* batches used during entire execution */

AggStatePerHash perhash; /* array of per-hashtable data */
AggStatePerGroup *hash_pergroup; /* grouping set indexed array of
* per-group pointers */

/* support for evaluation of agg input expressions: */
#define FIELDNO_AGGSTATE_ALL_PERGROUPS 49
AggStatePerGroup *all_pergroups; /* array of first ->pergroups, than
* ->hash_pergroup */
ProjectionInfo *combinedproj; /* projection machinery */

int group_id; /* GROUP_ID in current projection. This is passed
* to GroupingSetId expressions, similar to the
* 'grouped_cols' value. */
int gset_id;

/* if input tuple has an AggExprId, save the Attribute Number */
Index AggExprId_AttrNum;
} AggState;

他们之间的关系如下图所示:以投影中有聚合操作为例

#yyds干货盘点#GreenPlum7聚合_sed

下面分布对AggState中成员进行介绍。

ScanState中存储有聚合算子操作的计划节点描述信息PlanState。PlanState中有投影信息和执行计划树节点。计划节点Plan里的targetlist链表为聚合操作的一些相关信息。比如Aggref,aggref.args链表有针对哪一列进行聚合操作的信息。

AggState中的aggs链表存储有所有聚合操作函数的描述信息,最终aggref指向Plan的targetlist中。

aggstrategy指定聚合模式:有3中:
typedef enum AggStrategy
{
AGG_PLAIN, /* simple agg across all input rows */
AGG_SORTED, /* grouped agg, input must be sorted */
AGG_HASHED, /* grouped agg, use internal hashtable */
AGG_MIXED /* grouped agg, hash and sort both used */
} AggStrategy;

phase:聚合操作中间函数,比如avg的求和函数,的计算步骤。针对最终函数,并未为其进行表达式生成计算步骤,而是在finalize_aggregate函数中直接调用其函数进行计算。

peragg:聚合操作最终计算函数的元数据信息。这是一个数组,描述所有聚合操作的最终计算函数

pertrans:聚合操作中间函数的元数据信息。这也是一个数组。

pergroups:每个中间操作函数的返回值

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