PostgreSQL 源码解读（79）- 查询语句#64（create_plan函数#3-Se...

本节介绍了创建计划create_plan函数中扫描计划的实现过程，主要的逻辑在函数create_scan_plan中实现。

一、数据结构

Plan
所有计划节点通过将Plan结构作为第一个字段从Plan结构"派生"。这确保了在将节点转换为计划节点时，一切都能正常工作。(在执行器中以通用方式传递时，节点指针经常被转换为Plan *)

/* ---------------- *      Plan node * * All plan nodes "derive" from the Plan structure by having the * Plan structure as the first field.  This ensures that everything works * when nodes are cast to Plan's.  (node pointers are frequently cast to Plan* * when passed around generically in the executor) * 所有计划节点通过将Plan结构作为第一个字段从Plan结构"派生"。 * 这确保了在将节点转换为计划节点时，一切都能正常工作。 * (在执行器中以通用方式传递时，节点指针经常被转换为Plan *) * * We never actually instantiate any Plan nodes; this is just the common * abstract superclass for all Plan-type nodes. * 从未实例化任何Plan节点;这只是所有Plan-type节点的通用抽象超类。 * ---------------- */typedef struct Plan{    NodeTag     type;//节点类型    /*     * 成本估算信息;estimated execution costs for plan (see costsize.c for more info)     */    Cost        startup_cost;   /* 启动成本;cost expended before fetching any tuples */    Cost        total_cost;     /* 总成本;total cost (assuming all tuples fetched) */    /*     * 优化器估算信息;planner's estimate of result size of this plan step     */    double      plan_rows;      /* 行数;number of rows plan is expected to emit */    int         plan_width;     /* 平均行大小(Byte为单位);average row width in bytes */    /*     * 并行执行相关的信息;information needed for parallel query     */    bool        parallel_aware; /* 是否参与并行执行逻辑?engage parallel-aware logic? */    bool        parallel_safe;  /* 是否并行安全;OK to use as part of parallel plan? */    /*     * Plan类型节点通用的信息.Common structural data for all Plan types.     */    int         plan_node_id;   /* unique across entire final plan tree */    List       *targetlist;     /* target list to be computed at this node */    List       *qual;           /* implicitly-ANDed qual conditions */    struct Plan *lefttree;      /* input plan tree(s) */    struct Plan *righttree;    List       *initPlan;       /* Init Plan nodes (un-correlated expr                                 * subselects) */    /*     * Information for management of parameter-change-driven rescanning     * parameter-change-driven重扫描的管理信息.     *      * extParam includes the paramIDs of all external PARAM_EXEC params     * affecting this plan node or its children.  setParam params from the     * node's initPlans are not included, but their extParams are.     *     * allParam includes all the extParam paramIDs, plus the IDs of local     * params that affect the node (i.e., the setParams of its initplans).     * These are _all_ the PARAM_EXEC params that affect this node.     */    Bitmapset  *extParam;    Bitmapset  *allParam;} Plan;

二、源码解读

create_scan_plan函数创建Scan Plan.扫描可以分为顺序扫描(全表扫描)/索引扫描/索引快速扫描/TID扫描等多种扫描方式,这里主要介绍常见的顺序扫描和索引扫描,相应的实现函数是create_seqscan_plan和create_indexscan_plan.

//--------------------------------------------------- create_scan_plan/* * create_scan_plan *   Create a scan plan for the parent relation of 'best_path'. *   为relation best_path创建相应的扫描计划 */static Plan *create_scan_plan(PlannerInfo *root, Path *best_path, int flags){    RelOptInfo *rel = best_path->parent;    List       *scan_clauses;    List       *gating_clauses;    List       *tlist;    Plan       *plan;    /*     * Extract the relevant restriction clauses from the parent relation. The     * executor must apply all these restrictions during the scan, except for     * pseudoconstants which we'll take care of below.     * 从父关系中提取相关的限制条件。     * 执行器必须在扫描期间应用所有这些限制条件，除了伪常量，将在下面处理这些限制。     *     * If this is a plain indexscan or index-only scan, we need not consider     * restriction clauses that are implied by the index's predicate, so use     * indrestrictinfo not baserestrictinfo.  Note that we can't do that for     * bitmap indexscans, since there's not necessarily a single index     * involved; but it doesn't matter since create_bitmap_scan_plan() will be     * able to get rid of such clauses anyway via predicate proof.     * 如果这是一个普通的indexscan或index-only扫描，     * 则不需要考虑由索引谓词隐含的限制条款，因此使用indrestrictinfo而不是baserestrictinfo。     * 注意，对于位图索引扫描，我们不能这样做，因为不需要一个索引;     * 但是这并不重要，因为create_bitmap_scan_plan()将能够通过谓词证明消除这些子句。     */    switch (best_path->pathtype)    {        case T_IndexScan:        case T_IndexOnlyScan://索引扫描,使用索引约束条件            scan_clauses = castNode(IndexPath, best_path)->indexinfo->indrestrictinfo;            break;        default:            scan_clauses = rel->baserestrictinfo;//默认使用关系中的约束条件            break;    }    /*     * If this is a parameterized scan, we also need to enforce all the join     * clauses available from the outer relation(s).     * 如果这是一个参数化扫描,需要从连接外关系中加入所有可用的连接约束条件     *     * For paranoia's sake, don't modify the stored baserestrictinfo list.     * 由于paranoia's sake,不更新baserestrictinfo链表     */    if (best_path->param_info)        scan_clauses = list_concat(list_copy(scan_clauses),                                   best_path->param_info->ppi_clauses);    /*     * Detect whether we have any pseudoconstant quals to deal with.  Then, if     * we'll need a gating Result node, it will be able to project, so there     * are no requirements on the child's tlist.     * 检测是否有伪常数函数需要处理。     * 然后，需要一个能够执行投影的出口结果节点，因此对子tlist没有需求。     */    gating_clauses = get_gating_quals(root, scan_clauses);    if (gating_clauses)        flags = 0;    /*     * For table scans, rather than using the relation targetlist (which is     * only those Vars actually needed by the query), we prefer to generate a     * tlist containing all Vars in order.  This will allow the executor to     * optimize away projection of the table tuples, if possible.     * 对于表扫描，不使用关系targetlist(它只是查询实际需要的Vars)，     * 我们更喜欢按照顺序生成一个包含所有Vars的tlist。     * 如果可能的话，这将允许执行程序优化表元组的投影。     *     * But if the caller is going to ignore our tlist anyway, then don't     * bother generating one at all.  We use an exact equality test here, so     * that this only applies when CP_IGNORE_TLIST is the only flag set.     * 但是，如果调用者不管怎样都要忽略tlist，那么就根本不用去生成一个。     * 在这里使用了一个完全相等的测试，因此只有当CP_IGNORE_TLIST是唯一的标志设置时才适用。     */    if (flags == CP_IGNORE_TLIST)    {        tlist = NULL;//使用CP_IGNORE_TLIST标志,则设置tlist为NULL    }    else if (use_physical_tlist(root, best_path, flags))    {        if (best_path->pathtype == T_IndexOnlyScan)//索引快速扫描        {            /* For index-only scan, the preferred tlist is the index's */            //对于所有快速扫描,tlist中的列应在索引中            tlist = copyObject(((IndexPath *) best_path)->indexinfo->indextlist);            /*             * Transfer sortgroupref data to the replacement tlist, if             * requested (use_physical_tlist checked that this will work).             * 如需要,转换sortgroupref数据为tlist(use_physical_tlist检查是否可行)             */            if (flags & CP_LABEL_TLIST)                apply_pathtarget_labeling_to_tlist(tlist, best_path->pathtarget);        }        else//非索引快速扫描        {            tlist = build_physical_tlist(root, rel);//构建物理的tlist            if (tlist == NIL)            {                /* Failed because of dropped cols, so use regular method */                //build_physical_tlist无法构建,则使用常规方法构建                tlist = build_path_tlist(root, best_path);            }            else            {                /* As above, transfer sortgroupref data to replacement tlist */                if (flags & CP_LABEL_TLIST)                    apply_pathtarget_labeling_to_tlist(tlist, best_path->pathtarget);            }        }    }    else    {        tlist = build_path_tlist(root, best_path);//使用常规方法构建    }    switch (best_path->pathtype)//根据路径类型进行相应的处理    {        case T_SeqScan://顺序扫描            plan = (Plan *) create_seqscan_plan(root,                                                best_path,                                                tlist,                                                scan_clauses);            break;        case T_SampleScan:            plan = (Plan *) create_samplescan_plan(root,                                                   best_path,                                                   tlist,                                                   scan_clauses);            break;        case T_IndexScan:            plan = (Plan *) create_indexscan_plan(root,                                                  (IndexPath *) best_path,                                                  tlist,                                                  scan_clauses,                                                  false);            break;        case T_IndexOnlyScan:            plan = (Plan *) create_indexscan_plan(root,                                                  (IndexPath *) best_path,                                                  tlist,                                                  scan_clauses,                                                  true);            break;        case T_BitmapHeapScan:            plan = (Plan *) create_bitmap_scan_plan(root,                                                    (BitmapHeapPath *) best_path,                                                    tlist,                                                    scan_clauses);            break;        case T_TidScan:            plan = (Plan *) create_tidscan_plan(root,                                                (TidPath *) best_path,                                                tlist,                                                scan_clauses);            break;        case T_SubqueryScan:            plan = (Plan *) create_subqueryscan_plan(root,                                                     (SubqueryScanPath *) best_path,                                                     tlist,                                                     scan_clauses);            break;        case T_FunctionScan:            plan = (Plan *) create_functionscan_plan(root,                                                     best_path,                                                     tlist,                                                     scan_clauses);            break;        case T_TableFuncScan:            plan = (Plan *) create_tablefuncscan_plan(root,                                                      best_path,                                                      tlist,                                                      scan_clauses);            break;        case T_ValuesScan:            plan = (Plan *) create_valuesscan_plan(root,                                                   best_path,                                                   tlist,                                                   scan_clauses);            break;        case T_CteScan:            plan = (Plan *) create_ctescan_plan(root,                                                best_path,                                                tlist,                                                scan_clauses);            break;        case T_NamedTuplestoreScan:            plan = (Plan *) create_namedtuplestorescan_plan(root,                                                            best_path,                                                            tlist,                                                            scan_clauses);            break;        case T_WorkTableScan:            plan = (Plan *) create_worktablescan_plan(root,                                                      best_path,                                                      tlist,                                                      scan_clauses);            break;        case T_ForeignScan:            plan = (Plan *) create_foreignscan_plan(root,                                                    (ForeignPath *) best_path,                                                    tlist,                                                    scan_clauses);            break;        case T_CustomScan:            plan = (Plan *) create_customscan_plan(root,                                                   (CustomPath *) best_path,                                                   tlist,                                                   scan_clauses);            break;        default:            elog(ERROR, "unrecognized node type: %d",                 (int) best_path->pathtype);            plan = NULL;        /* keep compiler quiet */            break;    }    /*     * If there are any pseudoconstant clauses attached to this node, insert a     * gating Result node that evaluates the pseudoconstants as one-time     * quals.     * 如果这个节点上附加了伪常量子句，插入一个Result节点，该节点将伪常量计算为一次性的条件quals。     */    if (gating_clauses)        plan = create_gating_plan(root, best_path, plan, gating_clauses);    return plan;}//------------------------------------- create_seqscan_plan/* * create_seqscan_plan *   Returns a seqscan plan for the base relation scanned by 'best_path' *   with restriction clauses 'scan_clauses' and targetlist 'tlist'. *   返回seqscan顺序扫描计划(基于基本关系中的best_path),同时考虑了约束条件scan_clauses和投影列tlist */static SeqScan *create_seqscan_plan(PlannerInfo *root, Path *best_path,                    List *tlist, List *scan_clauses){    SeqScan    *scan_plan;    Index       scan_relid = best_path->parent->relid;    /* it should be a base rel... */    //基本关系    Assert(scan_relid > 0);    Assert(best_path->parent->rtekind == RTE_RELATION);    /* Sort clauses into best execution order */    //约束条件排序为最佳的执行顺序    scan_clauses = order_qual_clauses(root, scan_clauses);    /* Reduce RestrictInfo list to bare expressions; ignore pseudoconstants */    //规约限制条件信息链表到裸表达式,同时忽略pseudoconstants    scan_clauses = extract_actual_clauses(scan_clauses, false);    /* Replace any outer-relation variables with nestloop params */    //参数化访问,则使用内嵌循环参数替换外表变量    if (best_path->param_info)    {        scan_clauses = (List *)            replace_nestloop_params(root, (Node *) scan_clauses);//约束条件    }    scan_plan = make_seqscan(tlist,                             scan_clauses,                             scan_relid);//构建扫描计划    copy_generic_path_info(&scan_plan->plan, best_path);    return scan_plan;//返回}//------------------------------------- copy_generic_path_info /*  * Copy cost and size info from a Path node to the Plan node created from it.  * The executor usually won't use this info, but it's needed by EXPLAIN.  * Also copy the parallel-related flags, which the executor *will* use.  */ static void copy_generic_path_info(Plan *dest, Path *src) {     dest->startup_cost = src->startup_cost;     dest->total_cost = src->total_cost;     dest->plan_rows = src->rows;     dest->plan_width = src->pathtarget->width;     dest->parallel_aware = src->parallel_aware;     dest->parallel_safe = src->parallel_safe; } //------------------------------------- make_seqscanstatic SeqScan *make_seqscan(List *qptlist,             List *qpqual,             Index scanrelid){    SeqScan    *node = makeNode(SeqScan);    Plan       *plan = &node->plan;    plan->targetlist = qptlist;    plan->qual = qpqual;    plan->lefttree = NULL;    plan->righttree = NULL;    node->scanrelid = scanrelid;    return node;//创建节点}//------------------------------------- create_indexscan_plan/* * create_indexscan_plan *    Returns an indexscan plan for the base relation scanned by 'best_path' *    with restriction clauses 'scan_clauses' and targetlist 'tlist'. *    返回索引扫描计划 * * We use this for both plain IndexScans and IndexOnlyScans, because the * qual preprocessing work is the same for both.  Note that the caller tells * us which to build --- we don't look at best_path->path.pathtype, because * create_bitmap_subplan needs to be able to override the prior decision. * 此过程用于普通的indexscan和indexonlyscan，因为两者的条件qual预处理工作是相同的。 * 注意，调用者明确指示构建哪个--不需要查看best_path->path.pathtype， * 因为create_bitmap_subplan需要能够覆盖之前的决定。 */static Scan *create_indexscan_plan(PlannerInfo *root,                      IndexPath *best_path,                      List *tlist,                      List *scan_clauses,                      bool indexonly){    Scan       *scan_plan;    List       *indexquals = best_path->indexquals;    List       *indexorderbys = best_path->indexorderbys;    Index       baserelid = best_path->path.parent->relid;    Oid         indexoid = best_path->indexinfo->indexoid;    List       *qpqual;    List       *stripped_indexquals;    List       *fixed_indexquals;    List       *fixed_indexorderbys;    List       *indexorderbyops = NIL;    ListCell   *l;    /* it should be a base rel... */    //基本关系    Assert(baserelid > 0);    Assert(best_path->path.parent->rtekind == RTE_RELATION);    /*     * Build "stripped" indexquals structure (no RestrictInfos) to pass to     * executor as indexqualorig     * 构建"stripped"索引约束条件结构(非RestrictInfos),作为执行器的调用参数indexqualorig     */    stripped_indexquals = get_actual_clauses(indexquals);    /*     * The executor needs a copy with the indexkey on the left of each clause     * and with index Vars substituted for table ones.     * 执行器需要在每个子句的左边加上indexkey，并用索引变量替换表变量。     */    fixed_indexquals = fix_indexqual_references(root, best_path);    /*     * Likewise fix up index attr references in the ORDER BY expressions.     * 同样，修正ORDER BY 表达式的索引属性attr引用。     */    fixed_indexorderbys = fix_indexorderby_references(root, best_path);    /*     * The qpqual list must contain all restrictions not automatically handled     * by the index, other than pseudoconstant clauses which will be handled     * by a separate gating plan node.  All the predicates in the indexquals     * will be checked (either by the index itself, or by nodeIndexscan.c),     * but if there are any "special" operators involved then they must be     * included in qpqual.  The upshot is that qpqual must contain     * scan_clauses minus whatever appears in indexquals.     * qpqual链表必须包含索引未处理的其他限制条件，伪常量子句除外，伪常量子句将由单独的gating计划节点处理。     * indexquals中的所有谓词都将被检查(可以通过索引本身检查，也可以通过nodeIndexscan.c检查)，     * 但是如果涉及到任何"特殊"运算符，那么它们必须包含在qpqual中。     * 结果是，qpqual必须包含scan_clause，除去indexquals中出现的任何内容。     *      * In normal cases simple pointer equality checks will be enough to spot     * duplicate RestrictInfos, so we try that first.     * 在通常情况下，简单的指针相等检查将足以发现双重的RestrictInfos，因此首先执行此检查操作。     *     * Another common case is that a scan_clauses entry is generated from the     * same EquivalenceClass as some indexqual, and is therefore redundant     * with it, though not equal.  (This happens when indxpath.c prefers a     * different derived equality than what generate_join_implied_equalities     * picked for a parameterized scan's ppi_clauses.)     * 另一种常见的情况是scan_clauses entry是由与indexqual相同的EC生成的，因此尽管不相等但它是多余的。     * (这发生在indxpath.c与为参数化扫描的ppi_clauses与generate_join_implied_equalities选择的是不同的派生等式时)。     *     * In some situations (particularly with OR'd index conditions) we may     * have scan_clauses that are not equal to, but are logically implied by,     * the index quals; so we also try a predicate_implied_by() check to see     * if we can discard quals that way.  (predicate_implied_by assumes its     * first input contains only immutable functions, so we have to check     * that.)     * 在某些情况下(特别是在索引条件下)，可能有scan_clauses，虽然不等价,但逻辑上由索引quals表示;     * 因此，我们还尝试使用predicate_implied_by()检验是否这样丢弃quals。     * (predicate_implied_by假设它的第一个输入只包含不可变函数，所以必须检查它。)     *     * Note: if you change this bit of code you should also look at     * extract_nonindex_conditions() in costsize.c.     * 注意:如果需要这部分代码,需要检查costsize.c中的extract_nonindex_conditions()函数     */    qpqual = NIL;    foreach(l, scan_clauses)//遍历scan_clauses链表    {        RestrictInfo *rinfo = lfirst_node(RestrictInfo, l);        if (rinfo->pseudoconstant)            continue;           /* 不理会pseudoconstants;we may drop pseudoconstants here */        if (list_member_ptr(indexquals, rinfo))            continue;           /* 重复不处理;simple duplicate */        if (is_redundant_derived_clause(rinfo, indexquals))            continue;           /* 从EC中派生的不处理;derived from same EquivalenceClass */        if (!contain_mutable_functions((Node *) rinfo->clause) &&            predicate_implied_by(list_make1(rinfo->clause), indexquals, false))            continue;           /* 通过indexquals可隐式证明;provably implied by indexquals */        qpqual = lappend(qpqual, rinfo);    }    /* Sort clauses into best execution order */    //条件排序    qpqual = order_qual_clauses(root, qpqual);    /* Reduce RestrictInfo list to bare expressions; ignore pseudoconstants */    //规约    qpqual = extract_actual_clauses(qpqual, false);    /*     * We have to replace any outer-relation variables with nestloop params in     * the indexqualorig, qpqual, and indexorderbyorig expressions.  A bit     * annoying to have to do this separately from the processing in     * fix_indexqual_references --- rethink this when generalizing the inner     * indexscan support.  But note we can't really do this earlier because     * it'd break the comparisons to predicates above ... (or would it?  Those     * wouldn't have outer refs)     * 我们必须用indexqualorig、qpqual和indexorderbyorig表达式中的nestloop参数替换任何外关系变量。     * 与fix_indexqual_references中的处理分开来完成这一工作有点烦人--在泛化内部indexscan支持时重新考虑这一点。     * 但是请注意，不能提前做这个事情，因为它会打断与上面谓词的比较……(可能发生吗?因为它们没有外部依赖)     */    if (best_path->path.param_info)//存在参数信息,使用内嵌循环参数替换    {        stripped_indexquals = (List *)            replace_nestloop_params(root, (Node *) stripped_indexquals);        qpqual = (List *)            replace_nestloop_params(root, (Node *) qpqual);        indexorderbys = (List *)            replace_nestloop_params(root, (Node *) indexorderbys);    }    /*     * If there are ORDER BY expressions, look up the sort operators for their     * result datatypes.     * //存在ORDER BY表达式     */    if (indexorderbys)    {        ListCell   *pathkeyCell,                   *exprCell;        /*         * PathKey contains OID of the btree opfamily we're sorting by, but         * that's not quite enough because we need the expression's datatype         * to look up the sort operator in the operator family.         * PathKey已经包含我们正在排序的btree opfamily的OID，         * 但这还不足够，因为需要表达式的数据类型来查找操作符家族中的sort操作符。         */        Assert(list_length(best_path->path.pathkeys) == list_length(indexorderbys));        forboth(pathkeyCell, best_path->path.pathkeys, exprCell, indexorderbys)        {            PathKey    *pathkey = (PathKey *) lfirst(pathkeyCell);            Node       *expr = (Node *) lfirst(exprCell);            Oid         exprtype = exprType(expr);            Oid         sortop;            /* Get sort operator from opfamily */            sortop = get_opfamily_member(pathkey->pk_opfamily,                                         exprtype,                                         exprtype,                                         pathkey->pk_strategy);            if (!OidIsValid(sortop))                elog(ERROR, "missing operator %d(%u,%u) in opfamily %u",                     pathkey->pk_strategy, exprtype, exprtype, pathkey->pk_opfamily);            indexorderbyops = lappend_oid(indexorderbyops, sortop);        }    }    /* Finally ready to build the plan node */    //OK,下面可以构建计划节点了    if (indexonly)        scan_plan = (Scan *) make_indexonlyscan(tlist,                                                qpqual,                                                baserelid,                                                indexoid,                                                fixed_indexquals,                                                fixed_indexorderbys,                                                best_path->indexinfo->indextlist,                                                best_path->indexscandir);    else        scan_plan = (Scan *) make_indexscan(tlist,                                            qpqual,                                            baserelid,                                            indexoid,                                            fixed_indexquals,                                            stripped_indexquals,                                            fixed_indexorderbys,                                            indexorderbys,                                            indexorderbyops,                                            best_path->indexscandir);    copy_generic_path_info(&scan_plan->plan, &best_path->path);    return scan_plan;}//------------------------------------- make_indexscan/make_indexonlyscanstatic IndexScan *make_indexscan(List *qptlist,               List *qpqual,               Index scanrelid,               Oid indexid,               List *indexqual,               List *indexqualorig,               List *indexorderby,               List *indexorderbyorig,               List *indexorderbyops,               ScanDirection indexscandir){    IndexScan  *node = makeNode(IndexScan);    Plan       *plan = &node->scan.plan;    plan->targetlist = qptlist;    plan->qual = qpqual;    plan->lefttree = NULL;    plan->righttree = NULL;    node->scan.scanrelid = scanrelid;    node->indexid = indexid;    node->indexqual = indexqual;    node->indexqualorig = indexqualorig;    node->indexorderby = indexorderby;    node->indexorderbyorig = indexorderbyorig;    node->indexorderbyops = indexorderbyops;    node->indexorderdir = indexscandir;    return node;}static IndexOnlyScan *make_indexonlyscan(List *qptlist,                   List *qpqual,                   Index scanrelid,                   Oid indexid,                   List *indexqual,                   List *indexorderby,                   List *indextlist,                   ScanDirection indexscandir){    IndexOnlyScan *node = makeNode(IndexOnlyScan);    Plan       *plan = &node->scan.plan;    plan->targetlist = qptlist;    plan->qual = qpqual;    plan->lefttree = NULL;    plan->righttree = NULL;    node->scan.scanrelid = scanrelid;    node->indexid = indexid;    node->indexqual = indexqual;    node->indexorderby = indexorderby;    node->indextlist = indextlist;    node->indexorderdir = indexscandir;    return node;}

三、跟踪分析

测试脚本如下

testdb=# explain select dw.*,grjf.grbh,grjf.xm,grjf.ny,grjf.je testdb-# from t_dwxx dw,lateral (select gr.grbh,gr.xm,jf.ny,jf.je testdb(#                         from t_grxx gr inner join t_jfxx jf testdb(#                                        on gr.dwbh = dw.dwbh testdb(#                                           and gr.grbh = jf.grbh) grjftestdb-# where dw.dwbh in ('1001','1002')testdb-# order by dw.dwbh;                                          QUERY PLAN                                               ------------------------------------------------------------------------------------------------- Sort  (cost=2010.12..2010.17 rows=20 width=47)   Sort Key: dw.dwbh   ->  Nested Loop  (cost=14.24..2009.69 rows=20 width=47)         ->  Hash Join  (cost=13.95..2002.56 rows=20 width=32)               Hash Cond: ((gr.dwbh)::text = (dw.dwbh)::text)               ->  Seq Scan on t_grxx gr  (cost=0.00..1726.00 rows=100000 width=16)               ->  Hash  (cost=13.92..13.92 rows=2 width=20)                     ->  Index Scan using t_dwxx_pkey on t_dwxx dw  (cost=0.29..13.92 rows=2 width=20)                           Index Cond: ((dwbh)::text = ANY ('{1001,1002}'::text[]))         ->  Index Scan using idx_t_jfxx_grbh on t_jfxx jf  (cost=0.29..0.35 rows=1 width=20)               Index Cond: ((grbh)::text = (gr.grbh)::text)(11 rows)

启动gdb,设置断点,进入函数create_scan_plan

(gdb) b create_scan_planBreakpoint 1 at 0x7b7b78: file createplan.c, line 514.(gdb) cContinuing.Breakpoint 1, create_scan_plan (root=0x2d36d00, best_path=0x2d57ad0, flags=0) at createplan.c:514514     RelOptInfo *rel = best_path->parent;

pathtype为T_SeqScan

(gdb) p best_path->pathtype$1 = T_SeqScan

进入相应的分支,约束条件直接使用Relation的限制条件

(gdb) n532     switch (best_path->pathtype)(gdb) 539             scan_clauses = rel->baserestrictinfo;(gdb) 540             break;

非索引快速扫描,构建目标投影列

(gdb) n559     if (gating_clauses)(gdb) 572     if (flags == CP_IGNORE_TLIST)(gdb) 576     else if (use_physical_tlist(root, best_path, flags))(gdb) 578         if (best_path->pathtype == T_IndexOnlyScan)(gdb) 592             tlist = build_physical_tlist(root, rel);(gdb) 593             if (tlist == NIL)(gdb) 601                 if (flags & CP_LABEL_TLIST)(gdb) (gdb) p *tlist$4 = {type = T_List, length = 5, head = 0x2d89440, tail = 0x2d897d8}(gdb) p *(Node *)tlist->head->data.ptr_value$5 = {type = T_TargetEntry}(gdb) p *(TargetEntry *)tlist->head->data.ptr_value$6 = {xpr = {type = T_TargetEntry}, expr = 0x2d89390, resno = 1, resname = 0x0, ressortgroupref = 0, resorigtbl = 0,   resorigcol = 0, resjunk = false}

根据pathtype进入相应的处理逻辑,调用函数create_seqscan_plan

(gdb) n614             plan = (Plan *) create_seqscan_plan(root,(gdb) stepcreate_seqscan_plan (root=0x2d36d00, best_path=0x2d57ad0, tlist=0x2d89468, scan_clauses=0x0) at createplan.c:24442444        Index       scan_relid = best_path->parent->relid;

构建扫描条件,为NULL

2451        scan_clauses = order_qual_clauses(root, scan_clauses);(gdb) 2454        scan_clauses = extract_actual_clauses(scan_clauses, false);(gdb) 2457        if (best_path->param_info)(gdb) (gdb) p *scan_clausesCannot access memory at address 0x0

生成SeqScan Plan节点,并把启动成本/总成本等相关信息拷贝到该Plan中

(gdb) n2463        scan_plan = make_seqscan(tlist,(gdb) 2467        copy_generic_path_info(&scan_plan->plan, best_path);

完成创建,返回Plan

(gdb) n2469        return scan_plan;(gdb) p *scan_plan$1 = {plan = {type = T_SeqScan, startup_cost = 0, total_cost = 1726, plan_rows = 100000, plan_width = 16,     parallel_aware = false, parallel_safe = true, plan_node_id = 0, targetlist = 0x2db4e38, qual = 0x0, lefttree = 0x0,     righttree = 0x0, initPlan = 0x0, extParam = 0x0, allParam = 0x0}, scanrelid = 3}

下面跟踪分析create_indexscan_plan函数
设置断点,进入函数

(gdb) b create_indexscan_planBreakpoint 2 at 0x7badad: file createplan.c, line 2536.(gdb) cContinuing.Breakpoint 1, create_scan_plan (root=0x2d50a00, best_path=0x2da9e98, flags=2) at createplan.c:514514     RelOptInfo *rel = best_path->parent;(gdb) cContinuing.Breakpoint 2, create_indexscan_plan (root=0x2d50a00, best_path=0x2da9e98, tlist=0x2db5250, scan_clauses=0x2da8998,     indexonly=false) at createplan.c:25362536        List       *indexquals = best_path->indexquals;(gdb) 

赋值并获取相关信息

2536        List       *indexquals = best_path->indexquals;(gdb) n2537        List       *indexorderbys = best_path->indexorderbys;(gdb) 2538        Index       baserelid = best_path->path.parent->relid;(gdb) 2539        Oid         indexoid = best_path->indexinfo->indexoid;(gdb) 2544        List       *indexorderbyops = NIL;(gdb) 2548        Assert(baserelid > 0);(gdb) 2549        Assert(best_path->path.parent->rtekind == RTE_RELATION);(gdb) 2555        stripped_indexquals = get_actual_clauses(indexquals);(gdb) n2561        fixed_indexquals = fix_indexqual_references(root, best_path);(gdb) 2566        fixed_indexorderbys = fix_indexorderby_references(root, best_path);(gdb) 2596        qpqual = NIL;(gdb) (gdb) p baserelid$3 = 1(gdb) p indexoid$4 = 16738#t_dwxx_pkeytestdb=# select relname from pg_class where oid=16738;   relname   ------------- t_dwxx_pkey(1 row)

遍历扫描条件

2597        foreach(l, scan_clauses)(gdb) p *scan_clauses$5 = {type = T_List, length = 1, head = 0x2da8970, tail = 0x2da8970}

重复的约束条件,不需要处理

2603            if (list_member_ptr(indexquals, rinfo))(gdb) 2604                continue;           /* simple duplicate */

对条件进行排序&规约

2614        qpqual = order_qual_clauses(root, qpqual);(gdb) n2617        qpqual = extract_actual_clauses(qpqual, false);(gdb) n2628        if (best_path->path.param_info)(gdb) p *qpqualCannot access memory at address 0x0

创建IndexScan节点

(gdb) n2642        if (indexorderbys)(gdb) 2673        if (indexonly)(gdb) 2683            scan_plan = (Scan *) make_indexscan(tlist,(gdb) 2694        copy_generic_path_info(&scan_plan->plan, &best_path->path);(gdb) 2696        return scan_plan;(gdb) 2697    }(gdb) p *scan_plan$6 = {plan = {type = T_IndexScan, startup_cost = 0.28500000000000003, total_cost = 13.924222117799655, plan_rows = 2,     plan_width = 20, parallel_aware = false, parallel_safe = true, plan_node_id = 0, targetlist = 0x2db5250, qual = 0x0,     lefttree = 0x0, righttree = 0x0, initPlan = 0x0, extParam = 0x0, allParam = 0x0}, scanrelid = 1}(gdb) 

回到create_scan_plan

(gdb) ncreate_scan_plan (root=0x2d50a00, best_path=0x2da9e98, flags=2) at createplan.c:633633             break;(gdb) 732     if (gating_clauses)(gdb) 735     return plan;(gdb) 736 }

调用完成.

四、参考资料

createplan.c
PG Document:Query Planning