PostgreSQL 源码解读（192）- 查询#108(排序#1 - ExecInitSort)

本节介绍排序的实现,排序的实现函数是ExecSort,与聚合函数类似,也有要一个初始化的过程ExecInitSort,本节主要介绍该函数的实现.

下面是测试SQL执行排序的计划树:

",,,,,"select bh,c1 from t_sort order by t_sort;",,,"psql"2019-05-17 15:12:42.494 CST,"xdb","testdb",1519,"[local]",5cde5e9e.5ef,15,"SELECT",2019-05-17 15:11:26 CST,3/10,0,LOG,00000,"plan:","   {PLANNEDSTMT    :commandType 1    :queryId 0    :hasReturning false    :hasModifyingCTE false    :canSetTag true    :transientPlan false    :dependsOnRole false    :parallelModeNeeded false    :jitFlags 0    :planTree       {SORT       :startup_cost 14142.82       :total_cost 14392.82       :plan_rows 100000       :plan_width 66       :parallel_aware false       :parallel_safe true       :plan_node_id 0       :targetlist (...      )      :qual <>       :lefttree          {SEQSCAN          :startup_cost 0.00          :total_cost 1736.00          :plan_rows 100000          :plan_width 66          :parallel_aware false          :parallel_safe true          :plan_node_id 1          :targetlist (...         )         :qual <>          :lefttree <>          :righttree <>          :initPlan <>          :extParam (b)         :allParam (b)         :scanrelid 1         }      :righttree <>       :initPlan <>       :extParam (b)      :allParam (b)      :numCols 1       :sortColIdx 3       :sortOperators 2990       :collations 0       :nullsFirst false      }   :rtable (...   )   :resultRelations <>    :nonleafResultRelations <>    :rootResultRelations <>    :subplans <>    :rewindPlanIDs (b)   :rowMarks <>    :relationOids (o 278567)   :invalItems <>    :paramExecTypes <>    :utilityStmt <>    :stmt_location 0    :stmt_len 40   }",,,,,"select bh,c1 from t_sort order by t_sort;",,,"psql"

一、数据结构

SortState
排序运行期状态信息

/* ---------------- *     SortState information *     排序运行期状态信息 * ---------------- */typedef struct SortState{    //基类    ScanState    ss;                /* its first field is NodeTag */    //是否需要随机访问排序输出?    bool        randomAccess;    /* need random access to sort output? */    //结果集是否存在边界?    bool        bounded;        /* is the result set bounded? */    //如存在边界,需要多少个元组?    int64        bound;            /* if bounded, how many tuples are needed */    //是否已完成排序?    bool        sort_Done;        /* sort completed yet? */    //是否使用有界值?    bool        bounded_Done;    /* value of bounded we did the sort with */    //使用的有界值?    int64        bound_Done;        /* value of bound we did the sort with */    //tuplesort.c的私有状态    void       *tuplesortstate; /* private state of tuplesort.c */    //是否worker?    bool        am_worker;        /* are we a worker? */    //每个worker对应一个条目    SharedSortInfo *shared_info;    /* one entry per worker */} SortState;/* ---------------- *     Shared memory container for per-worker sort information *     per-worker排序信息的共享内存容器 * ---------------- */typedef struct SharedSortInfo{    //worker个数?    int            num_workers;    //排序机制    TuplesortInstrumentation sinstrument[FLEXIBLE_ARRAY_MEMBER];} SharedSortInfo;

TuplesortInstrumentation
报告排序统计的数据结构.

/* * Data structures for reporting sort statistics.  Note that * TuplesortInstrumentation can't contain any pointers because we * sometimes put it in shared memory. * 报告排序统计的数据结构. * 注意TuplesortInstrumentation不能包含指针因为有时候会把该结构体放在共享内存中. */typedef enum{    SORT_TYPE_STILL_IN_PROGRESS = 0,//仍然在排序中    SORT_TYPE_TOP_N_HEAPSORT,//TOP N 堆排序    SORT_TYPE_QUICKSORT,//快速排序    SORT_TYPE_EXTERNAL_SORT,//外部排序    SORT_TYPE_EXTERNAL_MERGE//外部排序后的合并} TuplesortMethod;//排序方法typedef enum{    SORT_SPACE_TYPE_DISK,//需要用上磁盘    SORT_SPACE_TYPE_MEMORY//使用内存} TuplesortSpaceType;typedef struct TuplesortInstrumentation{    //使用的排序算法    TuplesortMethod sortMethod; /* sort algorithm used */    //排序使用空间类型    TuplesortSpaceType spaceType;    /* type of space spaceUsed represents */    //空间消耗(以K为单位)    long        spaceUsed;        /* space consumption, in kB */} TuplesortInstrumentation;

二、源码解读

ExecInitSort为排序节点创建运行期信息并初始化outer子树,逻辑较为简单.

/* ---------------------------------------------------------------- *        ExecInitSort * *        Creates the run-time state information for the sort node *        produced by the planner and initializes its outer subtree. * ---------------------------------------------------------------- */SortState *ExecInitSort(Sort *node, EState *estate, int eflags){    SortState  *sortstate;//排序运行期信息    SO1_printf("ExecInitSort: %s\n",               "initializing sort node");    /*     * create state structure     * 创建运行期状态节点结构体     */    sortstate = makeNode(SortState);    sortstate->ss.ps.plan = (Plan *) node;    sortstate->ss.ps.state = estate;    sortstate->ss.ps.ExecProcNode = ExecSort;    /*     * We must have random access to the sort output to do backward scan or     * mark/restore.  We also prefer to materialize the sort output if we     * might be called on to rewind and replay it many times.     * 需要随机访问用于排序输出用于执行后端搜索或者标记/存储.     * 同时,如果可能在rewind或replay很多次的情况下,会倾向于物化排序输出     */    sortstate->randomAccess = (eflags & (EXEC_FLAG_REWIND |                                         EXEC_FLAG_BACKWARD |                                         EXEC_FLAG_MARK)) != 0;    sortstate->bounded = false;//结果集不存在边界    sortstate->sort_Done = false;//未完成排序    sortstate->tuplesortstate = NULL;//元组排序状态为NULL    /*     * Miscellaneous initialization     * 执行各种初始化     *     * Sort nodes don't initialize their ExprContexts because they never call     * ExecQual or ExecProject.     * 排序节点不需要初始化ExprContexts,因为排序不会调用ExecQual/ExecProject     */    /*     * initialize child nodes     * 初始化子节点     *     * We shield the child node from the need to support REWIND, BACKWARD, or     * MARK/RESTORE.     * 子节点不需要支持REWIND, BACKWARD, MARK/RESTORE     */    eflags &= ~(EXEC_FLAG_REWIND | EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK);    //外(左)子节点往往是扫描节点,如SeqScan等    outerPlanState(sortstate) = ExecInitNode(outerPlan(node), estate, eflags);    /*     * Initialize scan slot and type.     * 初始化扫描slot和类型     */    ExecCreateScanSlotFromOuterPlan(estate, &sortstate->ss);    /*     * Initialize return slot and type. No need to initialize projection info     * because this node doesn't do projections.     * 初始化返回slot和类型.     * 不需要初始化投影信息因为排序节点不需要投影.     */    ExecInitResultTupleSlotTL(estate, &sortstate->ss.ps);    sortstate->ss.ps.ps_ProjInfo = NULL;    SO1_printf("ExecInitSort: %s\n",               "sort node initialized");    return sortstate;}/* ---------------- *        ExecCreateSlotFromOuterPlan * ---------------- */voidExecCreateScanSlotFromOuterPlan(EState *estate, ScanState *scanstate){    PlanState  *outerPlan;    TupleDesc    tupDesc;    outerPlan = outerPlanState(scanstate);    tupDesc = ExecGetResultType(outerPlan);    ExecInitScanTupleSlot(estate, scanstate, tupDesc);}/* ---------------- *        ExecInitScanTupleSlot * ---------------- */voidExecInitScanTupleSlot(EState *estate, ScanState *scanstate, TupleDesc tupledesc){    scanstate->ss_ScanTupleSlot = ExecAllocTableSlot(&estate->es_tupleTable,                                                     tupledesc);    scanstate->ps.scandesc = tupledesc;}

三、跟踪分析

N/A

四、参考资料

N/A