Executor

执行器生命周期

阶段	核心函数	关键动作	节点操作
Init	ExecutorStart	解析计划树，构建运行时状态树，打开表，编译表达式。	ExecInitNode: Plan -> PlanState
Run	ExecutorRun	循环拉取数据，逐行处理，发送给客户端	ExecProcNode: TupleTableSlot, ExprContext
Finish	ExecutorFinish	执行排队的 AFTER 触发器，更新统计信息	AfterTriggerEndQuery
End	ExecutorEnd	关闭文件/扫描描述符，销毁临时占用资源	ExecEndNode

执行流程梳理

/* Portal & Executor */

CreatePortal

PortalDefineQuery // portal->stmts = plantree_list;

PortalStart // Prepare a portal for execution. params, strategy, queryDesc
    ExecutorStart // prepare the plan for execution
        standard_ExecutorStart
            InitPlan /* Initialize the plan state tree */
                ExecInitNode
                    ExecInitSeqScan
                        ExecOpenScanRelation
    PORTAL_READY

PortalRun - PortalRunSelect

    /* Executor */
    ExecutorRun - tandard_ExecutorRun - ExecutePlan // Processes the query plan until retrieved 'numberTuples' tuples
        ExecProcNode - ExecSeqScan
            ExecScan - ExecScanFetch - SeqNext // executor module
                /* Access + Storage*/
                table_scan_getnextslot - heap_getnextslot - heapgettup_pagemode
                    heapgetpage - ReadBufferExtended -  ReadBuffer_common

                        LockBuffer(buffer, BUFFER_LOCK_SHARE);

                        BufferGetPage - BufferGetBlock
                            return (Block) (BufferBlocks + ((Size) (buffer - 1)) * BLCKSZ);
                        for (lineoff = FirstOffsetNumber; lineoff <= lines; lineoff++)
                            PageGetItemId // Returns an item identifier of a page.
                                return &((PageHeader) page)->pd_linp[offsetNumber - 1];
                            PageGetItem // Retrieves an item on the given page.
                                return (Item) (((char *) page) + ItemIdGetOffset(itemId));

                        // True if heap tuple satisfies a time qual
                        HeapTupleSatisfiesVisibility - HeapTupleSatisfiesMVCC

                        LockBuffer(buffer, BUFFER_LOCK_UNLOCK);

                    ExecStorePinnedBufferHeapTuple // buffer tuple -> tuple table
                        tts_buffer_heap_store_tuple
                            IncrBufferRefCount
                            return slot;
                ExecProject

PortalDrop
    PortalCleanup
        ExecutorFinish
            ExecPostprocessPlan
            AfterTriggerEndQuery
        ExecutorEnd
            ExecEndPlan
                ExecEndNode
        FreeQueryDesc

    PortalHashTableDelete(portal)
    ResourceOwnerRelease
    MemoryContextDelete(portal->portalContext);
    pfree(portal);

finish_xact_command
    CommitTransactionCommand
        CommitTransaction

核心数据结构(TODO)

• Portal
• QueryDesc
• EState
• PlanState
• TupleTableSlot
• TupleDesc