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,主要是finalize_aggregates->finalize_aggregate. ### 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 **finalize_aggregate** finalize_aggregate计算聚合的最终结果,逻辑不复杂,自行查看源码. ``` /* * Compute the final value of one aggregate. * 计算聚合的最终结果 * * This function handles only one grouping set (already set in * aggstate->current_set). * 该函数只处理一个grouping set(已在aggstate->current_set中设置) * * The finalfunction will be run, and the result delivered, in the * output-tuple context; caller's CurrentMemoryContext does not matter. * 将执行finalfunction获得最终结果并存储在output-tuple上下文中. * 调用者的CurrentMemoryContext并不需要关心. * * The finalfn uses the state as set in the transno. This also might be * being used by another aggregate function, so it's important that we do * nothing destructive here. * finalfn使用在transno中设置运行状态. * 这可能会被其他聚合函数使用,因此不要做任何的重组. */ static void finalize_aggregate(AggState *aggstate, AggStatePerAgg peragg, AggStatePerGroup pergroupstate, Datum *resultVal, bool *resultIsNull) { FunctionCallInfoData fcinfo; bool anynull = false; MemoryContext oldContext; int i; ListCell *lc; AggStatePerTrans pertrans = &aggstate->pertrans[peragg->transno]; oldContext = MemoryContextSwitchTo(aggstate->ss.ps.ps_ExprContext->ecxt_per_tuple_memory); /* * Evaluate any direct arguments. We do this even if there's no finalfn * (which is unlikely anyway), so that side-effects happen as expected. * The direct arguments go into arg positions 1 and up, leaving position 0 * for the transition state value. * 解析所有的直接参数. * 就算没有任何finalfn(这看起来不太可能)也会做这个事情,因此会如期产生一些其他影响. * 直接参数进入arg位置1及以上，留出了位置0作为过渡状态值的位置。 */ i = 1; foreach(lc, peragg->aggdirectargs) { ExprState *expr = (ExprState *) lfirst(lc); //函数调用参数 fcinfo.arg[i] = ExecEvalExpr(expr, aggstate->ss.ps.ps_ExprContext, &fcinfo.argnull[i]); anynull |= fcinfo.argnull[i]; i++; } /* * Apply the agg's finalfn if one is provided, else return transValue. * 如有finalfn则执行该函数,否则直接返回transValue */ if (OidIsValid(peragg->finalfn_oid)) { int numFinalArgs = peragg->numFinalArgs; /* set up aggstate->curperagg for AggGetAggref() */ //为AggGetAggref()设置aggstate->curperagg aggstate->curperagg = peragg; //初始化函数调用信息 InitFunctionCallInfoData(fcinfo, &peragg->finalfn, numFinalArgs, pertrans->aggCollation, (void *) aggstate, NULL); /* Fill in the transition state value */ //填充转换状态值 fcinfo.arg[0] = MakeExpandedObjectReadOnly(pergroupstate->transValue, pergroupstate->transValueIsNull, pertrans->transtypeLen); fcinfo.argnull[0] = pergroupstate->transValueIsNull; anynull |= pergroupstate->transValueIsNull; /* Fill any remaining argument positions with nulls */ //使用nulls填充其他剩余参数 for (; i < numFinalArgs; i++) { fcinfo.arg[i] = (Datum) 0; fcinfo.argnull[i] = true; anynull = true; } if (fcinfo.flinfo->fn_strict && anynull) { /* don't call a strict function with NULL inputs */ //不要在调用严格函数时传递NULL参数 *resultVal = (Datum) 0; *resultIsNull = true; } else { //调用函数,获取结果值 *resultVal = FunctionCallInvoke(&fcinfo); *resultIsNull = fcinfo.isnull; } aggstate->curperagg = NULL; } else { /* Don't need MakeExpandedObjectReadOnly; datumCopy will copy it */ //不需要MakeExpandedObjectReadOnly,datumCopy会拷贝该数据. *resultVal = pergroupstate->transValue; *resultIsNull = pergroupstate->transValueIsNull; } /* * If result is pass-by-ref, make sure it is in the right context. * 如果结果通过引用传递,确保位于正确的上下文中. */ if (!peragg->resulttypeByVal && !*resultIsNull && !MemoryContextContains(CurrentMemoryContext, DatumGetPointer(*resultVal))) *resultVal = datumCopy(*resultVal, peragg->resulttypeByVal, peragg->resulttypeLen); MemoryContextSwitchTo(oldContext); } ``` ### 三、跟踪分析 测试脚本 ``` -- 禁用并行 set max_parallel_workers_per_gather=0; select bh,avg(c1),min(c1),max(c2) from t_agg_simple group by bh; ``` 跟踪分析 ``` (gdb) b finalize_aggregate Breakpoint 1 at 0x6ed256: file nodeAgg.c, line 901. (gdb) c Continuing. Breakpoint 1, finalize_aggregate (aggstate=0x154a640, peragg=0x154e390, pergroupstate=0x155f850, resultVal=0x154c0c8, resultIsNull=0x154c100) at nodeAgg.c:901 901 bool anynull = false; (gdb) ``` 输入参数 ``` (gdb) p *aggstate $1 = {ss = {ps = {type = T_AggState, plan = 0x1575890, state = 0x154a428, ExecProcNode = 0x6ee438 <ExecAgg>, ExecProcNodeReal = 0x6ee438 <ExecAgg>, instrument = 0x0, worker_instrument = 0x0, worker_jit_instrument = 0x0, qual = 0x0, lefttree = 0x154abb0, righttree = 0x0, initPlan = 0x0, subPlan = 0x0, chgParam = 0x0, ps_ResultTupleSlot = 0x154b7b0, ps_ExprContext = 0x154aaf0, ps_ProjInfo = 0x154b8f0, scandesc = 0x154af00}, ss_currentRelation = 0x0, ss_currentScanDesc = 0x0, ss_ScanTupleSlot = 0x154b458}, aggs = 0x154be00, numaggs = 3, numtrans = 3, aggstrategy = AGG_HASHED, aggsplit = AGGSPLIT_SIMPLE, phase = 0x154bef8, numphases = 1, current_phase = 0, peragg = 0x154e390, pertrans = 0x15673e0, hashcontext = 0x154aa30, aggcontexts = 0x154a858, tmpcontext = 0x154a878, curaggcontext = 0x154aa30, curperagg = 0x0, curpertrans = 0x1568c70, input_done = false, agg_done = false, projected_set = -1, current_set = 0, grouped_cols = 0x154c028, all_grouped_cols = 0x154c090, maxsets = 1, phases = 0x154bef8, sort_in = 0x0, sort_out = 0x0, sort_slot = 0x0, pergroups = 0x0, grp_firstTuple = 0x0, table_filled = true, num_hashes = 1, perhash = 0x154bf50, hash_pergroup = 0x154e5a8, all_pergroups = 0x154e5a8, combinedproj = 0x0} (gdb) p *peragg $2 = {aggref = 0x155b6e8, transno = 0, finalfn_oid = 0, finalfn = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0, fn_strict = false, fn_retset = false, fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0}, numFinalArgs = 1, aggdirectargs = 0x0, resulttypeLen = 4, resulttypeByVal = true, shareable = true} (gdb) p *pergroupstate $3 = {transValue = 5, transValueIsNull = false, noTransValue = false} (gdb) p *resultVal $4 = 0 (gdb) p *resultIsNull $5 = false (gdb) ``` 获取转换函数,切换上下文 ``` (gdb) n 905 AggStatePerTrans pertrans = &aggstate->pertrans[peragg->transno]; (gdb) 907 oldContext = MemoryContextSwitchTo(aggstate->ss.ps.ps_ExprContext->ecxt_per_tuple_memory); (gdb) 915 i = 1; (gdb) p *pertrans $6 = {aggref = 0x155b6e8, aggshared = false, numInputs = 1, numTransInputs = 1, transfn_oid = 768, serialfn_oid = 0, deserialfn_oid = 0, aggtranstype = 23, transfn = {fn_addr = 0x93e877 <int4larger>, fn_oid = 768, fn_nargs = 2, fn_strict = true, fn_retset = false, fn_stats = 2 '\002', fn_extra = 0x0, fn_mcxt = 0x154a310, fn_expr = 0x157a580}, serialfn = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0, fn_strict = false, fn_retset = false, fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0}, deserialfn = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0, fn_strict = false, fn_retset = false, fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0}, aggCollation = 0, numSortCols = 0, numDistinctCols = 0, sortColIdx = 0x0, sortOperators = 0x0, sortCollations = 0x0, sortNullsFirst = 0x0, equalfnOne = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0, fn_strict = false, fn_retset = false, fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0}, equalfnMulti = 0x0, initValue = 0, initValueIsNull = true, inputtypeLen = 0, transtypeLen = 4, inputtypeByVal = false, transtypeByVal = true, sortslot = 0x0, uniqslot = 0x0, sortdesc = 0x0, sortstates = 0x1550348, transfn_fcinfo = {flinfo = 0x1567408, context = 0x154a640, resultinfo = 0x0, fncollation = 0, isnull = false, nargs = 2, arg = {40, 50, 0 <repeats 98 times>}, argnull = {false <repeats 100 times>}}, serialfn_fcinfo = {flinfo = 0x0, context = 0x0, resultinfo = 0x0, fncollation = 0, isnull = false, nargs = 0, arg = {0 <repeats 100 times>}, argnull = { false <repeats 100 times>}}, deserialfn_fcinfo = {flinfo = 0x0, context = 0x0, resultinfo = 0x0, fncollation = 0, isnull = false, nargs = 0, arg = {0 <repeats 100 times>}, argnull = {false <repeats 100 times>}}} (gdb) ``` 解析所有的直接参数(无). ``` (gdb) n 916 foreach(lc, peragg->aggdirectargs) (gdb) p peragg->aggdirectargs $7 = (List *) 0x0 (gdb) n 930 if (OidIsValid(peragg->finalfn_oid)) (gdb) ``` 非有效的finalfn,直接赋值(这是max聚合) ``` (gdb) n 930 if (OidIsValid(peragg->finalfn_oid)) (gdb) p peragg->finalfn_oid $8 = 0 (gdb) n 973 *resultVal = pergroupstate->transValue; (gdb) 974 *resultIsNull = pergroupstate->transValueIsNull; (gdb) (gdb) p *resultVal $9 = 5 ``` 切换回原上下文 ``` (gdb) n 980 if (!peragg->resulttypeByVal && !*resultIsNull && (gdb) 987 MemoryContextSwitchTo(oldContext); (gdb) 988 } ``` 第2个聚合是min,同样没有finalfn ``` (gdb) n finalize_aggregates (aggstate=0x154a640, peraggs=0x154e390, pergroup=0x155f850) at nodeAgg.c:1160 1160 for (aggno = 0; aggno < aggstate->numaggs; aggno++) (gdb) c Continuing. Breakpoint 1, finalize_aggregate (aggstate=0x154a640, peragg=0x154e3e8, pergroupstate=0x155f860, resultVal=0x154c0d0, resultIsNull=0x154c101) at nodeAgg.c:901 901 bool anynull = false; (gdb) n 905 AggStatePerTrans pertrans = &aggstate->pertrans[peragg->transno]; (gdb) p *peragg $10 = {aggref = 0x155b460, transno = 1, finalfn_oid = 0, finalfn = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0, fn_strict = false, fn_retset = false, fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0}, numFinalArgs = 1, aggdirectargs = 0x0, resulttypeLen = 4, resulttypeByVal = true, shareable = true} (gdb) n 907 oldContext = MemoryContextSwitchTo(aggstate->ss.ps.ps_ExprContext->ecxt_per_tuple_memory); (gdb) p *pertrans $11 = {aggref = 0x155b460, aggshared = false, numInputs = 1, numTransInputs = 1, transfn_oid = 769, serialfn_oid = 0, deserialfn_oid = 0, aggtranstype = 23, transfn = {fn_addr = 0x93e8a3 <int4smaller>, fn_oid = 769, fn_nargs = 2, fn_strict = true, fn_retset = false, fn_stats = 2 '\002', fn_extra = 0x0, fn_mcxt = 0x154a310, fn_expr = 0x157a6d0}, serialfn = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0, fn_strict = false, fn_retset = false, fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0}, deserialfn = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0, fn_strict = false, fn_retset = false, fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0}, aggCollation = 0, numSortCols = 0, numDistinctCols = 0, sortColIdx = 0x0, sortOperators = 0x0, sortCollations = 0x0, sortNullsFirst = 0x0, equalfnOne = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0, fn_strict = false, fn_retset = false, fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0}, equalfnMulti = 0x0, initValue = 0, initValueIsNull = true, inputtypeLen = 0, transtypeLen = 4, inputtypeByVal = false, transtypeByVal = true, sortslot = 0x0, uniqslot = 0x0, sortdesc = 0x0, sortstates = 0x154e5d0, transfn_fcinfo = {flinfo = 0x1568050, context = 0x154a640, resultinfo = 0x0, fncollation = 0, isnull = false, nargs = 2, arg = {2, 50, 0 <repeats 98 times>}, argnull = {false <repeats 100 times>}}, serialfn_fcinfo = {flinfo = 0x0, context = 0x0, resultinfo = 0x0, fncollation = 0, isnull = false, nargs = 0, arg = {0 <repeats 100 times>}, argnull = {false <repeats 100 times>}}, deserialfn_fcinfo = {flinfo = 0x0, context = 0x0, resultinfo = 0x0, fncollation = 0, isnull = false, nargs = 0, arg = { 0 <repeats 100 times>}, argnull = {false <repeats 100 times>}}} (gdb) ``` 第3个聚合运算是avg,存在finalfn ``` (gdb) c Continuing. Breakpoint 1, finalize_aggregate (aggstate=0x154a640, peragg=0x154e440, pergroupstate=0x155f870, resultVal=0x154c0d8, resultIsNull=0x154c102) at nodeAgg.c:901 901 bool anynull = false; (gdb) n 905 AggStatePerTrans pertrans = &aggstate->pertrans[peragg->transno]; (gdb) 907 oldContext = MemoryContextSwitchTo(aggstate->ss.ps.ps_ExprContext->ecxt_per_tuple_memory); (gdb) p *pertrans $12 = {aggref = 0x155b1d8, aggshared = false, numInputs = 1, numTransInputs = 1, transfn_oid = 1963, serialfn_oid = 0, deserialfn_oid = 0, aggtranstype = 1016, transfn = {fn_addr = 0x977d8f <int4_avg_accum>, fn_oid = 1963, fn_nargs = 2, fn_strict = true, fn_retset = false, fn_stats = 2 '\002', fn_extra = 0x0, fn_mcxt = 0x154a310, fn_expr = 0x157aa40}, serialfn = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0, fn_strict = false, fn_retset = false, fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0}, deserialfn = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0, fn_strict = false, fn_retset = false, fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0}, aggCollation = 0, numSortCols = 0, numDistinctCols = 0, sortColIdx = 0x0, sortOperators = 0x0, sortCollations = 0x0, sortNullsFirst = 0x0, equalfnOne = {fn_addr = 0x0, fn_oid = 0, fn_nargs = 0, fn_strict = false, fn_retset = false, fn_stats = 0 '\000', fn_extra = 0x0, fn_mcxt = 0x0, fn_expr = 0x0}, equalfnMulti = 0x0, initValue = 22522136, initValueIsNull = false, inputtypeLen = 0, transtypeLen = -1, inputtypeByVal = false, transtypeByVal = false, sortslot = 0x0, uniqslot = 0x0, sortdesc = 0x0, sortstates = 0x154e5f0, transfn_fcinfo = {flinfo = 0x1568c98, context = 0x154a640, resultinfo = 0x0, fncollation = 0, isnull = false, nargs = 2, arg = {22410736, 50, 0 <repeats 98 times>}, argnull = {false <repeats 100 times>}}, serialfn_fcinfo = {flinfo = 0x0, context = 0x0, resultinfo = 0x0, fncollation = 0, isnull = false, nargs = 0, arg = {0 <repeats 100 times>}, argnull = { false <repeats 100 times>}}, deserialfn_fcinfo = {flinfo = 0x0, context = 0x0, resultinfo = 0x0, fncollation = 0, isnull = false, nargs = 0, arg = {0 <repeats 100 times>}, argnull = {false <repeats 100 times>}}} (gdb) p *peragg $13 = {aggref = 0x155b1d8, transno = 2, finalfn_oid = 1964, finalfn = {fn_addr = 0x978251 <int8_avg>, fn_oid = 1964, fn_nargs = 1, fn_strict = true, fn_retset = false, fn_stats = 2 '\002', fn_extra = 0x0, fn_mcxt = 0x154a310, fn_expr = 0x157a7c0}, numFinalArgs = 1, aggdirectargs = 0x0, resulttypeLen = -1, resulttypeByVal = false, shareable = true} (gdb) ``` 存在finalfn(int4_avg_accum) ``` (gdb) n 915 i = 1; (gdb) 916 foreach(lc, peragg->aggdirectargs) (gdb) 930 if (OidIsValid(peragg->finalfn_oid)) (gdb) p peragg->finalfn_oid $14 = 1964 (gdb) ``` 初始化函数调用信息&填充转换状态值&使用nulls填充其他剩余参数 ``` (gdb) n 932 int numFinalArgs = peragg->numFinalArgs; (gdb) 935 aggstate->curperagg = peragg; (gdb) p numFinalArgs $15 = 1 (gdb) n 937 InitFunctionCallInfoData(fcinfo, &peragg->finalfn, (gdb) 943 fcinfo.arg[0] = MakeExpandedObjectReadOnly(pergroupstate->transValue, (gdb) 946 fcinfo.argnull[0] = pergroupstate->transValueIsNull; (gdb) 947 anynull |= pergroupstate->transValueIsNull; (gdb) n 950 for (; i < numFinalArgs; i++) (gdb) p fcinfo $17 = {flinfo = 0x154e450, context = 0x154a640, resultinfo = 0x0, fncollation = 0, isnull = false, nargs = 1, arg = { 22411432, 4696688, 70368744179327, 262183, 0, 22291296, 22291800, 72057594037927952, 139949568947584, 532575944705, 139949566113024, 11508082471248244084, 139950313735104, 22291264, 140735692522224, 8884187, 0, 0, 481036337152, 22088784, 140735692522064, 22324800, 22522520, 22522520, 1, 22519768, 16302624, 140735692522192, 16302624, 139950284069640, 1, 22519768, 140735692522160, 22341032, 140735692522224, 4696688, 140735692525536, 0, 0, 7135662, 12884901892, 22326664, 7124177, 139950314519480, 139949574157416, 139949574157415, 0, 139949574157392, 0, 22449600, 139950314519224, 22410736, 140735692522336, 9928139, 140735692522336, 22449600, 125, 22291296, 4317427920, 536893372416, 140735692522368, 10923480, 536887362208, 22291264, 140735692522432, 8890594, 4294967296, 139949568947584, 22449600, 22410680, 16450208, 9441796618804569664, 140735692522548, 139949568947608, 125, 72057594060219232, 140735692522512, 8881213, 140735692522512, 16450208, 140735692522548, 139949568947608, 140735692522576, 8891011, 4317417729, 139949568947584, 9441796623099544216, 9441796618782244874, 16450208, 536893253520, 140735692522608, 8899958, 139949574149760, 536893253368, 140735692522640, 7227524, 4317293960, 22326664, 140735692522720, 7406960}, argnull = {false, 197, 245, 148, 255, 127, false, false, 176, 171, 84, true, false, false, false, false, 48, false, false, false, true, false <repeats 11 times>, 136, 173, 84, true, false, false, false, false, 232, 132, 87, true, true, false, false, false, 40, 164, 84, true, false, false, false, false, 104, 176, 87, true, false, false, false, false, 48, 197, 245, 148, 255, 127, false, false, 67, 35, 110, false, false, false, false, false, 32, 174, 84, true, false, false, false, false, 118, 5, 113, false, false, false, false, false, 171, 4, 113, false}} (gdb) (gdb) n 957 if (fcinfo.flinfo->fn_strict && anynull) (gdb) ``` 调用函数,获取结果值 ``` (gdb) n 965 *resultVal = FunctionCallInvoke(&fcinfo); (gdb) p *fcinfo.flinfo $18 = {fn_addr = 0x978251 <int8_avg>, fn_oid = 1964, fn_nargs = 1, fn_strict = true, fn_retset = false, fn_stats = 2 '\002', fn_extra = 0x0, fn_mcxt = 0x154a310, fn_expr = 0x157a7c0} (gdb) p *fcinfo.flinfo->fn_expr $19 = {type = T_FuncExpr} (gdb) b int8_avg Breakpoint 2 at 0x97825d: file numeric.c, line 5426. (gdb) ``` 进入int8_avg ``` (gdb) c Continuing. Breakpoint 2, int8_avg (fcinfo=0x7fff94f5c160) at numeric.c:5426 5426 ArrayType *transarray = PG_GETARG_ARRAYTYPE_P(0); (gdb) n 5431 if (ARR_HASNULL(transarray) || (gdb) 5432 ARR_SIZE(transarray) != ARR_OVERHEAD_NONULLS(1) + sizeof(Int8TransTypeData)) (gdb) 5431 if (ARR_HASNULL(transarray) || (gdb) 5434 transdata = (Int8TransTypeData *) ARR_DATA_PTR(transarray); (gdb) n 5437 if (transdata->count == 0) (gdb) p *transarray $1 = {vl_len_ = 160, ndim = 1, dataoffset = 0, elemtype = 20} (gdb) p *transdata $2 = {count = 2, sum = 55} (gdb) ``` 准备参数,调用numeric_div函数 ``` (gdb) n 5440 countd = DirectFunctionCall1(int8_numeric, (gdb) 5442 sumd = DirectFunctionCall1(int8_numeric, (gdb) 5445 PG_RETURN_DATUM(DirectFunctionCall2(numeric_div, sumd, countd)); (gdb) x/1xg countd 0x1572780: 0x0002800000000020 (gdb) x/1xg sumd 0x15727a0: 0x0037800000000020 ``` 调用完毕,回到finalize_aggregate ``` gdb) n 5446 } (gdb) finalize_aggregate (aggstate=0x1578960, peragg=0x157a730, pergroupstate=0x1570b40, resultVal=0x157a3f8, resultIsNull=0x157a422) at nodeAgg.c:966 966 *resultIsNull = fcinfo.isnull; (gdb) (gdb) p *resultVal $10 = 22489080 (gdb) p resultVal $11 = (Datum *) 0x157a3f8 (gdb) x/1xg resultVal 0x157a3f8: 0x00000000015727f8 (gdb) x/1fg resultVal 0x157a3f8: 1.1111081834575461e-316 (gdb) x/1fw resultVal 0x157a3f8: 3.95179395e-38 ``` DONE! ### 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](http://blog.itpub.net/6906/viewspace-2642505/)