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。

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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_seqscan

static 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_indexonlyscan
static 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) grjf
testdb-# 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_plan
Breakpoint 1 at 0x7b7b78: file createplan.c, line 514.
(gdb) c
Continuing.

Breakpoint 1, create_scan_plan (root=0x2d36d00, best_path=0x2d57ad0, flags=0) at createplan.c:514
514     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) n
532     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) n
559     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) n
614             plan = (Plan *) create_seqscan_plan(root,
(gdb) step
create_seqscan_plan (root=0x2d36d00, best_path=0x2d57ad0, tlist=0x2d89468, scan_clauses=0x0) at createplan.c:2444
2444        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_clauses
Cannot 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) n
2463        scan_plan = make_seqscan(tlist,
(gdb) 
2467        copy_generic_path_info(&scan_plan->plan, best_path);

完成创建,返回Plan

(gdb) n
2469        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_plan
Breakpoint 2 at 0x7badad: file createplan.c, line 2536.
(gdb) c
Continuing.

Breakpoint 1, create_scan_plan (root=0x2d50a00, best_path=0x2da9e98, flags=2) at createplan.c:514
514     RelOptInfo *rel = best_path->parent;
(gdb) c
Continuing.

Breakpoint 2, create_indexscan_plan (root=0x2d50a00, best_path=0x2da9e98, tlist=0x2db5250, scan_clauses=0x2da8998, 
    indexonly=false) at createplan.c:2536
2536        List       *indexquals = best_path->indexquals;
(gdb) 

赋值并获取相关信息

2536        List       *indexquals = best_path->indexquals;
(gdb) n
2537        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) n
2561        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_pkey
testdb=# 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) n
2617        qpqual = extract_actual_clauses(qpqual, false);
(gdb) n
2628        if (best_path->path.param_info)
(gdb) p *qpqual
Cannot access memory at address 0x0

创建IndexScan节点

(gdb) n
2642        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) n
create_scan_plan (root=0x2d50a00, best_path=0x2da9e98, flags=2) at createplan.c:633
633             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