PostgreSQL源码解读（189）-查询#105(聚合函数#10-agg_retrieve_hash_table)
本节继续介绍聚合函数的实现,主要介绍了agg_retrieve_hash_table函数中与投影相关的实现逻辑,包括函数prepare_projection_slot/finalize_aggregates/project_aggregates.
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一、数据结构
AggState
聚合函数执行时状态结构体,内含AggStatePerAgg等结构体
/* ---------------------
* AggState information
*
* ss.ss_ScanTupleSlot refers to output of underlying plan.
* ss.ss_ScanTupleSlot指的是基础计划的输出.
* (ss = ScanState,ps = PlanState)
*
* Note: ss.ps.ps_ExprContext contains ecxt_aggvalues and
* ecxt_aggnulls arrays, which hold the computed agg values for the current
* input group during evaluation of an Agg node's output tuple(s). We
* create a second ExprContext, tmpcontext, in which to evaluate input
* expressions and run the aggregate transition functions.
* 注意:ss.ps.ps_ExprContext包含了ecxt_aggvalues和ecxt_aggnulls数组,
* 这两个数组保存了在计算agg节点的输出元组时当前输入组已计算的agg值.
* ---------------------
*/
/* these structs are private in nodeAgg.c: */
//在nodeAgg.c中私有的结构体
typedef struct AggStatePerAggData *AggStatePerAgg;
typedef struct AggStatePerTransData *AggStatePerTrans;
typedef struct AggStatePerGroupData *AggStatePerGroup;
typedef struct AggStatePerPhaseData *AggStatePerPhase;
typedef struct AggStatePerHashData *AggStatePerHash;
typedef struct AggState
{
//第一个字段是NodeTag(继承自ScanState)
ScanState ss; /* its first field is NodeTag */
//targetlist和quals中所有的Aggref
List *aggs; /* all Aggref nodes in targetlist & quals */
//链表的大小(可以为0)
int numaggs; /* length of list (could be zero!) */
//pertrans条目大小
int numtrans; /* number of pertrans items */
//Agg策略模式
AggStrategy aggstrategy; /* strategy mode */
//agg-splitting模式,参见nodes.h
AggSplit aggsplit; /* agg-splitting mode, see nodes.h */
//指向当前步骤数据的指针
AggStatePerPhase phase; /* pointer to current phase data */
//步骤数(包括0)
int numphases; /* number of phases (including phase 0) */
//当前步骤
int current_phase; /* current phase number */
//per-Aggref信息
AggStatePerAgg peragg; /* per-Aggref information */
//per-Trans状态信息
AggStatePerTrans pertrans; /* per-Trans state information */
//长生命周期数据的ExprContexts(hashtable)
ExprContext *hashcontext; /* econtexts for long-lived data (hashtable) */
////长生命周期数据的ExprContexts(每一个GS使用)
ExprContext **aggcontexts; /* econtexts for long-lived data (per GS) */
//输入表达式的ExprContext
ExprContext *tmpcontext; /* econtext for input expressions */
#define FIELDNO_AGGSTATE_CURAGGCONTEXT 14
//当前活跃的aggcontext
ExprContext *curaggcontext; /* currently active aggcontext */
//当前活跃的aggregate(如存在)
AggStatePerAgg curperagg; /* currently active aggregate, if any */
#define FIELDNO_AGGSTATE_CURPERTRANS 16
//当前活跃的trans state
AggStatePerTrans curpertrans; /* currently active trans state, if any */
//输入结束?
bool input_done; /* indicates end of input */
//Agg扫描结束?
bool agg_done; /* indicates completion of Agg scan */
//最后一个grouping set
int projected_set; /* The last projected grouping set */
#define FIELDNO_AGGSTATE_CURRENT_SET 20
//将要解析的当前grouping set
int current_set; /* The current grouping set being evaluated */
//当前投影操作的分组列
Bitmapset *grouped_cols; /* grouped cols in current projection */
//倒序的分组列链表
List *all_grouped_cols; /* list of all grouped cols in DESC order */
/* These fields are for grouping set phase data */
//-------- 下面的列用于grouping set步骤数据
//所有步骤中最大的sets大小
int maxsets; /* The max number of sets in any phase */
//所有步骤的数组
AggStatePerPhase phases; /* array of all phases */
//对于phases > 1,已排序的输入信息
Tuplesortstate *sort_in; /* sorted input to phases > 1 */
//对于下一个步骤,输入已拷贝
Tuplesortstate *sort_out; /* input is copied here for next phase */
//排序结果的slot
TupleTableSlot *sort_slot; /* slot for sort results */
/* these fields are used in AGG_PLAIN and AGG_SORTED modes: */
//------- 下面的列用于AGG_PLAIN和AGG_SORTED模式:
//per-group指针的grouping set编号数组
AggStatePerGroup *pergroups; /* grouping set indexed array of per-group
* pointers */
//当前组的第一个元组拷贝
HeapTuple grp_firstTuple; /* copy of first tuple of current group */
/* these fields are used in AGG_HASHED and AGG_MIXED modes: */
//--------- 下面的列用于AGG_HASHED和AGG_MIXED模式:
//是否已填充hash表?
bool table_filled; /* hash table filled yet? */
//hash桶数?
int num_hashes;
//相应的哈希表数据数组
AggStatePerHash perhash; /* array of per-hashtable data */
//per-group指针的grouping set编号数组
AggStatePerGroup *hash_pergroup; /* grouping set indexed array of
* per-group pointers */
/* support for evaluation of agg input expressions: */
//---------- agg输入表达式解析支持
#define FIELDNO_AGGSTATE_ALL_PERGROUPS 34
//首先是->pergroups,然后是hash_pergroup
AggStatePerGroup *all_pergroups; /* array of first ->pergroups, than
* ->hash_pergroup */
//投影实现机制
ProjectionInfo *combinedproj; /* projection machinery */
} AggState;
/* Primitive options supported by nodeAgg.c: */
//nodeag .c支持的基本选项
#define AGGSPLITOP_COMBINE 0x01 /* substitute combinefn for transfn */
#define AGGSPLITOP_SKIPFINAL 0x02 /* skip finalfn, return state as-is */
#define AGGSPLITOP_SERIALIZE 0x04 /* apply serializefn to output */
#define AGGSPLITOP_DESERIALIZE 0x08 /* apply deserializefn to input */
/* Supported operating modes (i.e., useful combinations of these options): */
//支持的操作模式
typedef enum AggSplit
{
/* Basic, non-split aggregation: */
//基本 : 非split聚合
AGGSPLIT_SIMPLE = 0,
/* Initial phase of partial aggregation, with serialization: */
//部分聚合的初始步骤,序列化
AGGSPLIT_INITIAL_SERIAL = AGGSPLITOP_SKIPFINAL | AGGSPLITOP_SERIALIZE,
/* Final phase of partial aggregation, with deserialization: */
//部分聚合的最终步骤,反序列化
AGGSPLIT_FINAL_DESERIAL = AGGSPLITOP_COMBINE | AGGSPLITOP_DESERIALIZE
} AggSplit;
/* Test whether an AggSplit value selects each primitive option: */
//测试AggSplit选择了哪些基本选项
#define DO_AGGSPLIT_COMBINE(as) (((as) & AGGSPLITOP_COMBINE) != 0)
#define DO_AGGSPLIT_SKIPFINAL(as) (((as) & AGGSPLITOP_SKIPFINAL) != 0)
#define DO_AGGSPLIT_SERIALIZE(as) (((as) & AGGSPLITOP_SERIALIZE) != 0)
#define DO_AGGSPLIT_DESERIALIZE(as) (((as) & AGGSPLITOP_DESERIALIZE) != 0)
二、源码解读
prepare_projection_slot
prepare_projection_slot函数基于指定的典型元组slot和grouping set准备finalize和project.
比如初始化isnull数组等.
/*
* Prepare to finalize and project based on the specified representative tuple
* slot and grouping set.
* 基于指定的典型元组slot和grouping set准备finalize和project.
*
* In the specified tuple slot, force to null all attributes that should be
* read as null in the context of the current grouping set. Also stash the
* current group bitmap where GroupingExpr can get at it.
* 在指定的元组slot,强制在当前grouping set上下文中应为null的所有属性值为null.
* 还可以将当前组位图保存在GroupingExpr可以获得的位置.
*
* This relies on three conditions:
* 这取决于下面3个条件:
*
* 1) Nothing is ever going to try and extract the whole tuple from this slot,
* only reference it in evaluations, which will only access individual
* attributes.
* 1) 永远不会尝试从该slot中提取整个元组,只是在解析中依赖它,这只会访问单个属性.
*
* 2) No system columns are going to need to be nulled. (If a system column is
* referenced in a group clause, it is actually projected in the outer plan
* tlist.)
* 2) 系统列不需要设置为null.
* (如在group语句中依赖系统列,实际上已在outer plan tlist中已完成投影)
*
* 3) Within a given phase, we never need to recover the value of an attribute
* once it has been set to null.
* 3) 在给定的阶段,一旦属性被设置为null,就不需要恢复属性值.
*
* Poking into the slot this way is a bit ugly, but the consensus is that the
* alternative was worse.
* 以这种方法使用slot有点丑陋,但其他方式更糟糕.
*/
static void
prepare_projection_slot(AggState *aggstate, TupleTableSlot *slot, int currentSet)
{
if (aggstate->phase->grouped_cols)
{
Bitmapset *grouped_cols = aggstate->phase->grouped_cols[currentSet];
aggstate->grouped_cols = grouped_cols;
if (slot->tts_isempty)
{
/*
* Force all values to be NULL if working on an empty input tuple
* (i.e. an empty grouping set for which no input rows were
* supplied).
* 如输入tuple为空,则强制所有值为NULL.
* (如不提供输入行的空grouping set)
*/
ExecStoreAllNullTuple(slot);
}
else if (aggstate->all_grouped_cols)
{
ListCell *lc;
/* all_grouped_cols is arranged in desc order */
//all_grouped_cols以倒序的方式组织
slot_getsomeattrs(slot, linitial_int(aggstate->all_grouped_cols));
foreach(lc, aggstate->all_grouped_cols)
{
int attnum = lfirst_int(lc);
if (!bms_is_member(attnum, grouped_cols))
slot->tts_isnull[attnum - 1] = true;
}
}
}
}
finalize_aggregates
finalize_aggregates函数计算某一组所有聚合的最终值,实现函数是finalize_aggregate,该实现函数下节再行介绍.
/*
* Compute the final value of all aggregates for one group.
* 计算某一组所有聚合的最终值
*
* This function handles only one grouping set at a time, which the caller must
* have selected. It's also the caller's responsibility to adjust the supplied
* pergroup parameter to point to the current set's transvalues.
* 该函数一次只会处理一个grouping set(调用者负责选择).
* 调用者同样有职责调整提供的pergroup参数为指向当前集合的transvalues.
*
* Results are stored in the output econtext aggvalues/aggnulls.
*/
static void
finalize_aggregates(AggState *aggstate,
AggStatePerAgg peraggs,
AggStatePerGroup pergroup)
{
ExprContext *econtext = aggstate->ss.ps.ps_ExprContext;
Datum *aggvalues = econtext->ecxt_aggvalues;
bool *aggnulls = econtext->ecxt_aggnulls;
int aggno;
int transno;
/*
* If there were any DISTINCT and/or ORDER BY aggregates, sort their
* inputs and run the transition functions.
* 如存在DISTINCT或ORDER BY 聚合,排序这些输入并执行转换函数.
*/
//遍历转换函数
for (transno = 0; transno < aggstate->numtrans; transno++)
{
//转换函数
AggStatePerTrans pertrans = &aggstate->pertrans[transno];
//pergroup
AggStatePerGroup pergroupstate;
pergroupstate = &pergroup[transno];
if (pertrans->numSortCols > 0)
{
//--- 存在DISTINCT/ORDER BY
//验证,Hash不需要排序
Assert(aggstate->aggstrategy != AGG_HASHED &&
aggstate->aggstrategy != AGG_MIXED);
if (pertrans->numInputs == 1)
//单独
process_ordered_aggregate_single(aggstate,
pertrans,
pergroupstate);
else
//多个
process_ordered_aggregate_multi(aggstate,
pertrans,
pergroupstate);
}
}
/*
* Run the final functions.
* 执行获取最终值的函数
*/
//遍历聚合
for (aggno = 0; aggno < aggstate->numaggs; aggno++)
{
//获取peragg
AggStatePerAgg peragg = &peraggs[aggno];
int transno = peragg->transno;
AggStatePerGroup pergroupstate;
//pergroup
pergroupstate = &pergroup[transno];
if (DO_AGGSPLIT_SKIPFINAL(aggstate->aggsplit))
//并行处理结果
finalize_partialaggregate(aggstate, peragg, pergroupstate,
&aggvalues[aggno], &aggnulls[aggno]);
else
//调用finalize_aggregate获取结果
finalize_aggregate(aggstate, peragg, pergroupstate,
&aggvalues[aggno], &aggnulls[aggno]);
}
}
project_aggregates
project_aggregates函数投影某一组的结果(该组结果已通过finalize_aggregates函数计算得到).
/*
* Project the result of a group (whose aggs have already been calculated by
* finalize_aggregates). Returns the result slot, or NULL if no row is
* projected (suppressed by qual).
* 投影某一组的结果(该组结果已通过finalize_aggregates函数计算得到).
* 返回结果slot,如无结果行投影(通过qual处理)则返回NULL.
*/
static TupleTableSlot *
project_aggregates(AggState *aggstate)
{
ExprContext *econtext = aggstate->ss.ps.ps_ExprContext;
/*
* Check the qual (HAVING clause); if the group does not match, ignore it.
* 检查条件表达式(HAVING子句).如跟group不匹配,则忽略之.
*/
if (ExecQual(aggstate->ss.ps.qual, econtext))
{
/*
* Form and return projection tuple using the aggregate results and
* the representative input tuple.
* 使用聚合结果和相应的输入tuple组成并返回投影元组.
*/
return ExecProject(aggstate->ss.ps.ps_ProjInfo);
}
else
InstrCountFiltered1(aggstate, 1);
return NULL;
}
#define InstrCountFiltered1(node, delta) \
do { \
if (((PlanState *)(node))->instrument) \
((PlanState *)(node))->instrument->nfiltered1 += (delta); \
} while(0)
ExecProject
ExecProject函数基于投影信息投影元组并把元组存储在传递给ExecBuildProjectInfo()的slot参数中.
/*
* ExecProject
*
* Projects a tuple based on projection info and stores it in the slot passed
* to ExecBuildProjectInfo().
* 基于投影信息投影元组并把元组存储在传递给ExecBuildProjectInfo()的slot参数中.
*
* Note: the result is always a virtual tuple; therefore it may reference
* the contents of the exprContext's scan tuples and/or temporary results
* constructed in the exprContext. If the caller wishes the result to be
* valid longer than that data will be valid, he must call ExecMaterializeSlot
* on the result slot.
* 注意:结果通常是虚拟元组.因此该元组可能会依赖exprContext扫描元组的内容和/或在exprContext中构建的临时结果.
* 如果调用者希望结果比数据更长久有效,调用者必须调用在结果slot上调用ExecMaterializeSlot(物化).
*/
#ifndef FRONTEND
static inline TupleTableSlot *
ExecProject(ProjectionInfo *projInfo)
{
ExprContext *econtext = projInfo->pi_exprContext;
ExprState *state = &projInfo->pi_state;
TupleTableSlot *slot = state->resultslot;
bool isnull;
/*
* Clear any former contents of the result slot. This makes it safe for
* us to use the slot's Datum/isnull arrays as workspace.
* 清理结果slot的形式内容.
* 这可以确保slot的Datum/isnull数组是OK的.
*/
ExecClearTuple(slot);
/* Run the expression, discarding scalar result from the last column. */
//执行表达式解析,丢弃scalar结果.
(void) ExecEvalExprSwitchContext(state, econtext, &isnull);
/*
* Successfully formed a result row. Mark the result slot as containing a
* valid virtual tuple (inlined version of ExecStoreVirtualTuple()).
* 成功组成一个结果行.
* 标记结果slot为包含有效虚拟元组(内联版本的ExecStoreVirtualTuple)
*/
slot->tts_isempty = false;
slot->tts_nvalid = slot->tts_tupleDescriptor->natts;
return slot;
}
#endif
三、跟踪分析
N/A
四、参考资料
PostgreSQL 源码解读（178）- 查询#95(聚合函数)#1相关数据结构
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