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PostgreSQL 源码解读(231)- 查询#124(NOT IN实现#2)

原创 PostgreSQL 作者:husthxd 时间:2019-10-17 15:04:34 0 删除 编辑

本节介绍了PostgreSQL含有NOT IN查询语句实现中的ExecMaterial函数.

一、数据结构

SubPlanState
子计划运行期状态


/* ----------------
 *        SubPlanState node
 * ----------------
 */
typedef struct SubPlanState
{
    NodeTag        type;
    SubPlan    *subplan;        /* expression plan node */
    struct PlanState *planstate;    /* subselect plan's state tree */
    struct PlanState *parent;    /* parent plan node's state tree */
    ExprState  *testexpr;        /* 组合表达式状态;state of combining expression */
    List       *args;            /* 参数表达式状态;states of argument expression(s) */
    HeapTuple    curTuple;        /* subplan最近的元组;copy of most recent tuple from subplan */
    Datum        curArray;        /* most recent array from ARRAY() subplan */
    /* these are used when hashing the subselect's output: */
    TupleDesc    descRight;        /* 投影后的子查询描述符;subselect desc after projection */
    ProjectionInfo *projLeft;    /* for projecting lefthand exprs */
    ProjectionInfo *projRight;    /* for projecting subselect output */
    TupleHashTable hashtable;    /* hash table for no-nulls subselect rows */
    TupleHashTable hashnulls;    /* hash table for rows with null(s) */
    bool        havehashrows;    /* true if hashtable is not empty */
    bool        havenullrows;    /* true if hashnulls is not empty */
    MemoryContext hashtablecxt; /* memory context containing hash tables */
    MemoryContext hashtempcxt;    /* temp memory context for hash tables */
    ExprContext *innerecontext; /* econtext for computing inner tuples */
    AttrNumber *keyColIdx;        /* control data for hash tables */
    Oid           *tab_eq_funcoids;    /* equality func oids for table
                                     * datatype(s) */
    Oid           *tab_collations; /* collations for hash and comparison */
    FmgrInfo   *tab_hash_funcs; /* hash functions for table datatype(s) */
    FmgrInfo   *tab_eq_funcs;    /* equality functions for table datatype(s) */
    FmgrInfo   *lhs_hash_funcs; /* hash functions for lefthand datatype(s) */
    FmgrInfo   *cur_eq_funcs;    /* equality functions for LHS vs. table */
    ExprState  *cur_eq_comp;    /* equality comparator for LHS vs. table */
} SubPlanState;

SubPlan
子查询计划


/*
 * SubPlan - executable expression node for a subplan (sub-SELECT)
 *
 * The planner replaces SubLink nodes in expression trees with SubPlan
 * nodes after it has finished planning the subquery.  SubPlan references
 * a sub-plantree stored in the subplans list of the toplevel PlannedStmt.
 * (We avoid a direct link to make it easier to copy expression trees
 * without causing multiple processing of the subplan.)
 * 查询规划器在完成子查询的规划后使用SubPlan节点替换表达式树中的SubLink节点。
 * SubPlan引用了存储在高层PlannedStmt中的subplans链表中的sub-plantree。
 * (避免使用直接链接,从而使得拷贝表达式树相对比较简单)
 *
 * In an ordinary subplan, testexpr points to an executable expression
 * (OpExpr, an AND/OR tree of OpExprs, or RowCompareExpr) for the combining
 * operator(s); the left-hand arguments are the original lefthand expressions,
 * and the right-hand arguments are PARAM_EXEC Param nodes representing the
 * outputs of the sub-select.  (NOTE: runtime coercion functions may be
 * inserted as well.)  This is just the same expression tree as testexpr in
 * the original SubLink node, but the PARAM_SUBLINK nodes are replaced by
 * suitably numbered PARAM_EXEC nodes.
 * 常规情况下,testexpr指向用于组合操作的可执行表达式(OpExpr、OpExprs的AND/OR树或者RowCompareExpr);
 * 左参数是原始的左表达式,右参数是PARAM_EXEC参数节点用以表示子查询的输出。
 * 与原始SubLink节点的testexpr具有相同的表达式树,但PARAM_SUBLINK节点则使用合适的已编号PARAM_EXEC节点替代。
 *
 * If the sub-select becomes an initplan rather than a subplan, the executable
 * expression is part of the outer plan's expression tree (and the SubPlan
 * node itself is not, but rather is found in the outer plan's initPlan
 * list).  In this case testexpr is NULL to avoid duplication.
 * 如果子查询成了initplan而不是subplan,可执行的表达式是外层plan表达式树的一部分。
 * 这种情况下,testexpr为NULL以避免重复。
 *
 * The planner also derives lists of the values that need to be passed into
 * and out of the subplan.  Input values are represented as a list "args" of
 * expressions to be evaluated in the outer-query context (currently these
 * args are always just Vars, but in principle they could be any expression).
 * The values are assigned to the global PARAM_EXEC params indexed by parParam
 * (the parParam and args lists must have the same ordering).  setParam is a
 * list of the PARAM_EXEC params that are computed by the sub-select, if it
 * is an initplan; they are listed in order by sub-select output column
 * position.  (parParam and setParam are integer Lists, not Bitmapsets,
 * because their ordering is significant.)
 * 规划器还派生了需要传入和传出子计划的值的链表。
 * 输入值标识位表达式的“args”链表,在外层查询上下文中进行解析。
 * (这些args通常是Vars,但原则上它们可以是任意表达式)
 * 这些值以parParam为索引给全局PARAM_EXEC参数赋值。
 * setParam是PARAM_EXEC参数链表,通过子查询(如为initplan)计算所得。
 * 它们按子查询输出列的位置进行排序组织为链表形式。
 * (parParam和setParam是整型链表,而不是Bitmapsets链表)
 *
 * Also, the planner computes startup and per-call costs for use of the
 * SubPlan.  Note that these include the cost of the subquery proper,
 * evaluation of the testexpr if any, and any hashtable management overhead.
 * 同时,规划器计算SubPlan启动和每次调用的成本。注意:包括子查询正常解析testexpr的成本以及哈希表管理成本。
 */
typedef struct SubPlan
{
    Expr        xpr;//表达式
    /* Fields copied from original SubLink: */
    //从SubLink中拷贝而来
    SubLinkType subLinkType;    /* see above */
    /* The combining operators, transformed to an executable expression: */
    //组合操作符,转换为可执行的表达式
    Node       *testexpr;        /* OpExpr or RowCompareExpr expression tree */
    List       *paramIds;        /* 参数IDs;IDs of Params embedded in the above */
    /* Identification of the Plan tree to use: */
    //Plan tree标识
    int            plan_id;        /* Index (from 1) in PlannedStmt.subplans */
    /* Identification of the SubPlan for EXPLAIN and debugging purposes: */
    //EXPLAIN和debug目的的SubPlan标识
    char       *plan_name;        /* A name assigned during planning */
    /* Extra data useful for determining subplan's output type: */
    //用于确定subplan输出类型的额外信息
    Oid            firstColType;    /* subplan结果的第一个列类型;Type of first column of subplan result */
    int32        firstColTypmod; /* 第一列的Typmod;Typmod of first column of subplan result */
    Oid            firstColCollation;    /* 第一列的Collation;Collation of first column of subplan
                                     * result */
    /* Information about execution strategy: */
    //执行阶段的相关信息
    bool        useHashTable;    /* 是否使用哈希表存储子查询输出;true to store subselect output in a hash
                                 * table (implies we are doing "IN") */
    bool        unknownEqFalse; /* 如OK为T,如为未知则为F;快速处理null值;true if it's okay to return FALSE when the
                                 * spec result is UNKNOWN; this allows much
                                 * simpler handling of null values */
    bool        parallel_safe;    /* 是否并行安全?is the subplan parallel-safe? */
    /* Note: parallel_safe does not consider contents of testexpr or args */
    /* Information for passing params into and out of the subselect: */
    //用于给子查询传入和传出参数的信息
    /* setParam and parParam are lists of integers (param IDs) */
    //setParam和parParam是整型链表(param IDs)
    List       *setParam;        /* initplan subqueries have to set these
                                 * Params for parent plan */
    List       *parParam;        /* indices of input Params from parent plan */
    List       *args;            /* 以parParam值进行传递的表达式;exprs to pass as parParam values */
    /* Estimated execution costs: */
    //估算执行成本
    Cost        startup_cost;    /* one-time setup cost */
    Cost        per_call_cost;    /* cost for each subplan evaluation */
} SubPlan;

SubLinkType
SubLink类型


/*
 * SubLink
 *
 * A SubLink represents a subselect appearing in an expression, and in some
 * cases also the combining operator(s) just above it.  The subLinkType
 * indicates the form of the expression represented:
 *    EXISTS_SUBLINK        EXISTS(SELECT ...)
 *    ALL_SUBLINK            (lefthand) op ALL (SELECT ...)
 *    ANY_SUBLINK            (lefthand) op ANY (SELECT ...)
 *    ROWCOMPARE_SUBLINK    (lefthand) op (SELECT ...)
 *    EXPR_SUBLINK        (SELECT with single targetlist item ...)
 *    MULTIEXPR_SUBLINK    (SELECT with multiple targetlist items ...)
 *    ARRAY_SUBLINK        ARRAY(SELECT with single targetlist item ...)
 *    CTE_SUBLINK            WITH query (never actually part of an expression)
 * For ALL, ANY, and ROWCOMPARE, the lefthand is a list of expressions of the
 * same length as the subselect's targetlist.  ROWCOMPARE will *always* have
 * a list with more than one entry; if the subselect has just one target
 * then the parser will create an EXPR_SUBLINK instead (and any operator
 * above the subselect will be represented separately).
 * ROWCOMPARE, EXPR, and MULTIEXPR require the subselect to deliver at most
 * one row (if it returns no rows, the result is NULL).
 * ALL, ANY, and ROWCOMPARE require the combining operators to deliver boolean
 * results.  ALL and ANY combine the per-row results using AND and OR
 * semantics respectively.
 * ARRAY requires just one target column, and creates an array of the target
 * column's type using any number of rows resulting from the subselect.
 *
 * SubLink is classed as an Expr node, but it is not actually executable;
 * it must be replaced in the expression tree by a SubPlan node during
 * planning.
 *
 * NOTE: in the raw output of gram.y, testexpr contains just the raw form
 * of the lefthand expression (if any), and operName is the String name of
 * the combining operator.  Also, subselect is a raw parsetree.  During parse
 * analysis, the parser transforms testexpr into a complete boolean expression
 * that compares the lefthand value(s) to PARAM_SUBLINK nodes representing the
 * output columns of the subselect.  And subselect is transformed to a Query.
 * This is the representation seen in saved rules and in the rewriter.
 *
 * In EXISTS, EXPR, MULTIEXPR, and ARRAY SubLinks, testexpr and operName
 * are unused and are always null.
 *
 * subLinkId is currently used only for MULTIEXPR SubLinks, and is zero in
 * other SubLinks.  This number identifies different multiple-assignment
 * subqueries within an UPDATE statement's SET list.  It is unique only
 * within a particular targetlist.  The output column(s) of the MULTIEXPR
 * are referenced by PARAM_MULTIEXPR Params appearing elsewhere in the tlist.
 *
 * The CTE_SUBLINK case never occurs in actual SubLink nodes, but it is used
 * in SubPlans generated for WITH subqueries.
 */
typedef enum SubLinkType
{
    EXISTS_SUBLINK,
    ALL_SUBLINK,
    ANY_SUBLINK,
    ROWCOMPARE_SUBLINK,
    EXPR_SUBLINK,
    MULTIEXPR_SUBLINK,
    ARRAY_SUBLINK,
    CTE_SUBLINK                    /* for SubPlans only */
} SubLinkType;

SubLink
SubLink结构体


typedef struct SubLink
{
    Expr        xpr;
    SubLinkType subLinkType;    /* see above */
    int            subLinkId;        /* ID (1..n); 0 if not MULTIEXPR */
    Node       *testexpr;        /* outer-query test for ALL/ANY/ROWCOMPARE */
    List       *operName;        /* originally specified operator name */
    Node       *subselect;        /* subselect as Query* or raw parsetree */
    int            location;        /* token location, or -1 if unknown */
} SubLink;

MaterialState
Material状态

/* ----------------
 *     MaterialState information
 *
 *        materialize nodes are used to materialize the results
 *        of a subplan into a temporary file.
 *        materialize节点用于物化subplan的结果为临时文件。
 *
 *        ss.ss_ScanTupleSlot refers to output of underlying plan.
 *        ss.ss_ScanTupleSlot指向underlyling plan的输出(subplan)
 * ----------------
 */
typedef struct MaterialState
{
    ScanState    ss;                /* its first field is NodeTag */
    int            eflags;            /* 传递给tuplestore的capability标记;capability flags to pass to tuplestore */
    bool        eof_underlying; /* 已经到达underlying plan的末尾?reached end of underlying plan? */
    Tuplestorestate *tuplestorestate;
} MaterialState;

二、源码解读



/* ----------------------------------------------------------------
 *        ExecMaterial
 *
 *        As long as we are at the end of the data collected in the tuplestore,
 *        we collect one new row from the subplan on each call, and stash it
 *        aside in the tuplestore before returning it.  The tuplestore is
 *        only read if we are asked to scan backwards, rescan, or mark/restore.
 *      只要在tuplestore中数据收集结束时,就会在每次调用时从subplan中收集一条新行,
 *      并在返回之前将其保存在tuplestore中。
 *      只要在往后扫描、重新扫描或标记/恢复时tuplestore才会读取。
 *
 * ----------------------------------------------------------------
 */
static TupleTableSlot *            /* 从subplan中返回的结果;result tuple from subplan */
ExecMaterial(PlanState *pstate)
{
    MaterialState *node = castNode(MaterialState, pstate);//物化节点
    EState       *estate;//运行期状态
    ScanDirection dir;//扫描方向
    bool        forward;//是否往前扫描
    Tuplestorestate *tuplestorestate;//Tuplestorestate结构体指针
    bool        eof_tuplestore;//是否完成?
    TupleTableSlot *slot;//存储元组的slot
    CHECK_FOR_INTERRUPTS();
    /*
     * get state info from node
     * 从物化节点中获取相关信息
     */
    estate = node->ss.ps.state;
    dir = estate->es_direction;//方向
    forward = ScanDirectionIsForward(dir);//是否往前扫描
    tuplestorestate = node->tuplestorestate;
    /*
     * If first time through, and we need a tuplestore, initialize it.
     * 第一次,需要tuplestore并初始化
     */
    if (tuplestorestate == NULL && node->eflags != 0)
    {
        tuplestorestate = tuplestore_begin_heap(true, false, work_mem);
        tuplestore_set_eflags(tuplestorestate, node->eflags);
        if (node->eflags & EXEC_FLAG_MARK)
        {
            /*
             * Allocate a second read pointer to serve as the mark. We know it
             * must have index 1, so needn't store that.
             * 分配用于mark的读指针
             */
            int            ptrno PG_USED_FOR_ASSERTS_ONLY;
            ptrno = tuplestore_alloc_read_pointer(tuplestorestate,
                                                  node->eflags);
            Assert(ptrno == 1);
        }
        node->tuplestorestate = tuplestorestate;
    }
    /*
     * If we are not at the end of the tuplestore, or are going backwards, try
     * to fetch a tuple from tuplestore.
     * 如果不在tuplestore的末尾或者正在往后扫描,尝试从tuplestore中提取一个元组
     */
    eof_tuplestore = (tuplestorestate == NULL) ||
        tuplestore_ateof(tuplestorestate);
    if (!forward && eof_tuplestore)
    {
        if (!node->eof_underlying)
        {
            /*
             * When reversing direction at tuplestore EOF, the first
             * gettupleslot call will fetch the last-added tuple; but we want
             * to return the one before that, if possible. So do an extra
             * fetch.
             * 在EOF处反转方向,第一次的gettupleslot调用会提取最后添加的元组;
             * 但如可能,希望返回在此之前的元组,执行额外的提取操作。
             */
            if (!tuplestore_advance(tuplestorestate, forward))
                return NULL;    /* the tuplestore must be empty */
        }
        eof_tuplestore = false;
    }
    /*
     * If we can fetch another tuple from the tuplestore, return it.
     * 如能从tuplestore中提取另外一个tuple,返回
     */
    slot = node->ss.ps.ps_ResultTupleSlot;
    if (!eof_tuplestore)
    {
        if (tuplestore_gettupleslot(tuplestorestate, forward, false, slot))
            return slot;
        if (forward)
            eof_tuplestore = true;
    }
    /*
     * If necessary, try to fetch another row from the subplan.
     * 如需要(tuplestore末尾),尝试从subplan中提取另外一行
     *
     * Note: the eof_underlying state variable exists to short-circuit further
     * subplan calls.  It's not optional, unfortunately, because some plan
     * node types are not robust about being called again when they've already
     * returned NULL.
     */
    if (eof_tuplestore && !node->eof_underlying)
    {
        PlanState  *outerNode;
        TupleTableSlot *outerslot;
        /*
         * We can only get here with forward==true, so no need to worry about
         * which direction the subplan will go.
         */
        outerNode = outerPlanState(node);
        outerslot = ExecProcNode(outerNode);
        if (TupIsNull(outerslot))
        {
            node->eof_underlying = true;
            return NULL;
        }
        /*
         * Append a copy of the returned tuple to tuplestore.  NOTE: because
         * the tuplestore is certainly in EOF state, its read position will
         * move forward over the added tuple.  This is what we want.
         * 追加返回的元组到tuplestore中。
         * 注意:因为tuplestore当前处于EOF状态,读取的位置会前移至已添加的tuple前面,这是我们希望看到的。
         */
        if (tuplestorestate)
            tuplestore_puttupleslot(tuplestorestate, outerslot);
        ExecCopySlot(slot, outerslot);
        return slot;
    }
    /*
     * Nothing left ...
     */
    return ExecClearTuple(slot);
}

三、跟踪分析

执行SQL:

[pg12@localhost ~]$ psql -d testdb
Timing is on.
Expanded display is used automatically.
psql (12.0)
Type "help" for help.
[local]:5432 pg12@testdb=# 
[local]:5432 pg12@testdb=# select * from tbl;
 id | value 
----+-------
  1 |     2
(1 row)
Time: 2.678 ms
[local]:5432 pg12@testdb=# select count(*) from t_big_null;
  count   
----------
 10000001
(1 row)
Time: 679.972 ms
[local]:5432 pg12@testdb=# analyze tbl;
ANALYZE
Time: 64.442 ms
[local]:5432 pg12@testdb=# analyze t_big_null;
ANALYZE
Time: 434.702 ms
[local]:5432 pg12@testdb=# 
[local]:5432 pg12@testdb=# select pg_backend_pid();
 pg_backend_pid 
----------------
          18758
(1 row)
Time: 1.990 ms
[local]:5432 pg12@testdb=# select * from tbl a where a.id not in (select b.id from t_big_null b);

启动gdb跟踪

(gdb) b ExecMaterial
Breakpoint 1 at 0x720edb: file nodeMaterial.c, line 41.
(gdb) c
Continuing.
Breakpoint 1, ExecMaterial (pstate=0x1230128) at nodeMaterial.c:41
41        MaterialState *node = castNode(MaterialState, pstate);
(gdb)

输入参数

(gdb) p *pstate
$4 = {type = T_MaterialState, plan = 0x1211858, state = 0x122fe88, 
  ExecProcNode = 0x720ecf <ExecMaterial>, ExecProcNodeReal = 0x720ecf <ExecMaterial>, 
  instrument = 0x0, worker_instrument = 0x0, worker_jit_instrument = 0x0, qual = 0x0, 
  lefttree = 0x1230240, righttree = 0x0, initPlan = 0x0, subPlan = 0x0, chgParam = 0x0, 
  ps_ResultTupleDesc = 0x1230660, ps_ResultTupleSlot = 0x1230778, ps_ExprContext = 0x0, 
  ps_ProjInfo = 0x0, scandesc = 0x1230548, scanops = 0xc3e720 <TTSOpsMinimalTuple>, 
  outerops = 0x0, innerops = 0x0, resultops = 0xc3e720 <TTSOpsMinimalTuple>, 
  scanopsfixed = true, outeropsfixed = false, inneropsfixed = false, 
  resultopsfixed = true, scanopsset = true, outeropsset = false, inneropsset = false, 
  resultopsset = true}
(gdb)

MaterialState结构体指针数据

(gdb) p *node
$1 = {ss = {ps = {type = T_MaterialState, plan = 0x1211858, state = 0x122fe88, 
      ExecProcNode = 0x720ecf <ExecMaterial>, ExecProcNodeReal = 0x720ecf <ExecMaterial>, 
      instrument = 0x0, worker_instrument = 0x0, worker_jit_instrument = 0x0, qual = 0x0, 
      lefttree = 0x1230240, righttree = 0x0, initPlan = 0x0, subPlan = 0x0, 
      chgParam = 0x0, ps_ResultTupleDesc = 0x1230660, ps_ResultTupleSlot = 0x1230778, 
      ps_ExprContext = 0x0, ps_ProjInfo = 0x0, scandesc = 0x1230548, 
      scanops = 0xc3e720 <TTSOpsMinimalTuple>, outerops = 0x0, innerops = 0x0, 
      resultops = 0xc3e720 <TTSOpsMinimalTuple>, scanopsfixed = true, 
      outeropsfixed = false, inneropsfixed = false, resultopsfixed = true, 
      scanopsset = true, outeropsset = false, inneropsset = false, resultopsset = true}, 
    ss_currentRelation = 0x0, ss_currentScanDesc = 0x0, ss_ScanTupleSlot = 0x1230838}, 
  eflags = 2, eof_underlying = false, tuplestorestate = 0x0}
(gdb) p *node->ss->ps->plan
$2 = {type = T_Material, startup_cost = 0, total_cost = 233310.685, plan_rows = 9999979, 
  plan_width = 4, parallel_aware = false, parallel_safe = true, plan_node_id = 1, 
  targetlist = 0x1257600, qual = 0x0, lefttree = 0x1210f58, righttree = 0x0, 
  initPlan = 0x0, extParam = 0x0, allParam = 0x0}
(gdb)

运行期信息和方向

(gdb) p *estate
$5 = {type = T_EState, es_direction = ForwardScanDirection, es_snapshot = 0x1164d50, 
  es_crosscheck_snapshot = 0x0, es_range_table = 0x1257328, 
  es_range_table_array = 0x12300d8, es_range_table_size = 2, es_relations = 0x1230100, 
  es_rowmarks = 0x0, es_plannedstmt = 0x1257748, 
  es_sourceText = 0x113cd88 "select * from tbl a where a.id not in (select b.id from t_big_null b);", es_junkFilter = 0x0, es_output_cid = 0, es_result_relations = 0x0, 
  es_num_result_relations = 0, es_result_relation_info = 0x0, 
  es_root_result_relations = 0x0, es_num_root_result_relations = 0, 
  es_partition_directory = 0x0, es_tuple_routing_result_relations = 0x0, 
  es_trig_target_relations = 0x0, es_param_list_info = 0x0, 
  es_param_exec_vals = 0x12300a0, es_queryEnv = 0x0, es_query_cxt = 0x122fd70, 
  es_tupleTable = 0x1230510, es_processed = 0, es_top_eflags = 16, es_instrument = 0, 
  es_finished = false, es_exprcontexts = 0x1230418, es_subplanstates = 0x1230920, 
  es_auxmodifytables = 0x0, es_per_tuple_exprcontext = 0x0, es_epq_active = 0x0, 
  es_use_parallel_mode = false, es_query_dsa = 0x0, es_jit_flags = 25, es_jit = 0x0, 
  es_jit_worker_instr = 0x0}
(gdb) p dir
$6 = ForwardScanDirection
(gdb)

初始化tuplestore

(gdb) n
64            tuplestorestate = tuplestore_begin_heap(true, false, work_mem);
(gdb) n
65            tuplestore_set_eflags(tuplestorestate, node->eflags);
(gdb) p *tuplestorestate
$7 = {status = TSS_INMEM, eflags = 6, backward = false, interXact = false, 
  truncated = false, availMem = 4177896, allowedMem = 4194304, tuples = 0, myfile = 0x0, 
  context = 0x122fd70, resowner = 0x116e308, copytup = 0xaba7bd <copytup_heap>, 
  writetup = 0xaba811 <writetup_heap>, readtup = 0xaba9d9 <readtup_heap>, 
  memtuples = 0x1219e60, memtupdeleted = 0, memtupcount = 0, memtupsize = 2048, 
  growmemtuples = true, readptrs = 0x123ca50, activeptr = 0, readptrcount = 1, 
  readptrsize = 8, writepos_file = 0, writepos_offset = 0}
(gdb) n
66            if (node->eflags & EXEC_FLAG_MARK)
(gdb) 
78            node->tuplestorestate = tuplestorestate;
(gdb) 
85        eof_tuplestore = (tuplestorestate == NULL) ||
(gdb) p *tuplestorestate
$8 = {status = TSS_INMEM, eflags = 2, backward = false, interXact = false, 
  truncated = false, availMem = 4177896, allowedMem = 4194304, tuples = 0, myfile = 0x0, 
  context = 0x122fd70, resowner = 0x116e308, copytup = 0xaba7bd <copytup_heap>, 
  writetup = 0xaba811 <writetup_heap>, readtup = 0xaba9d9 <readtup_heap>, 
  memtuples = 0x1219e60, memtupdeleted = 0, memtupcount = 0, memtupsize = 2048, 
  growmemtuples = true, readptrs = 0x123ca50, activeptr = 0, readptrcount = 1, 
  readptrsize = 8, writepos_file = 0, writepos_offset = 0}
(gdb)

既不是往后扫描也没有到达EOF

(gdb) n
86            tuplestore_ateof(tuplestorestate);
(gdb) 
85        eof_tuplestore = (tuplestorestate == NULL) ||
(gdb) 
88        if (!forward && eof_tuplestore)
(gdb) p eof_tuplestore
$9 = false
(gdb) p forward
$10 = true
(gdb)

如能从tuplestore中提取另外一个tuple,则返回此slot

(gdb) n
107        slot = node->ss.ps.ps_ResultTupleSlot;
(gdb) 
108        if (!eof_tuplestore)
(gdb) p *slot
$11 = {type = T_TupleTableSlot, tts_flags = 18, tts_nvalid = 0, 
  tts_ops = 0xc3e720 <TTSOpsMinimalTuple>, tts_tupleDescriptor = 0x1230660, 
  tts_values = 0x12307e8, tts_isnull = 0x12307f0, tts_mcxt = 0x122fd70, tts_tid = {
    ip_blkid = {bi_hi = 65535, bi_lo = 65535}, ip_posid = 0}, tts_tableOid = 0}
(gdb) p slot->tts_values[0]
$12 = 0
(gdb) n
110            if (tuplestore_gettupleslot(tuplestorestate, forward, false, slot))
(gdb)

如扫描方向为往前,则设置eof_tuplestore为T,填充tuple到tuplestore中

112            if (forward)
(gdb) 
113                eof_tuplestore = true;
(gdb)

如需要(处于tuplestore末尾),尝试从subplan(扫描t_big_null)中提取另外一行

124        if (eof_tuplestore && !node->eof_underlying)
(gdb) p node->eof_underlying
$13 = false
(gdb) n
133            outerNode = outerPlanState(node);
(gdb) n
134            outerslot = ExecProcNode(outerNode);
(gdb) 
135            if (TupIsNull(outerslot))
(gdb) p *outerNode
$14 = {type = T_SeqScanState, plan = 0x1210f58, state = 0x122fe88, 
  ExecProcNode = 0x72b904 <ExecSeqScan>, ExecProcNodeReal = 0x72b904 <ExecSeqScan>, 
  instrument = 0x0, worker_instrument = 0x0, worker_jit_instrument = 0x0, qual = 0x0, 
  lefttree = 0x0, righttree = 0x0, initPlan = 0x0, subPlan = 0x0, chgParam = 0x0, 
  ps_ResultTupleDesc = 0x1230548, ps_ResultTupleSlot = 0x0, ps_ExprContext = 0x1230358, 
  ps_ProjInfo = 0x0, scandesc = 0x7f6ec53386a8, 
  scanops = 0xc3e780 <TTSOpsBufferHeapTuple>, outerops = 0x0, innerops = 0x0, 
  resultops = 0xc3e780 <TTSOpsBufferHeapTuple>, scanopsfixed = true, 
  outeropsfixed = false, inneropsfixed = false, resultopsfixed = true, scanopsset = true, 
  outeropsset = false, inneropsset = false, resultopsset = true}
(gdb) p *outerslot
$15 = {type = T_TupleTableSlot, tts_flags = 16, tts_nvalid = 0, 
  tts_ops = 0xc3e780 <TTSOpsBufferHeapTuple>, tts_tupleDescriptor = 0x7f6ec53386a8, 
  tts_values = 0x12304c0, tts_isnull = 0x12304c8, tts_mcxt = 0x122fd70, tts_tid = {
    ip_blkid = {bi_hi = 0, bi_lo = 44240}, ip_posid = 1}, tts_tableOid = 49155}
(gdb) p outerslot->tts_values[0]
$16 = 0
(gdb) p outerslot->tts_values[1]
$17 = 0
(gdb) 
###
[local]:5432 pg12@testdb=# select oid,relname from pg_class where oid = 49155;
  oid  |  relname   
-------+------------
 49155 | t_big_null
(1 row)
###

拷贝到tuplestore中,返回slot

(gdb) n
146            if (tuplestorestate)
(gdb) 
147                tuplestore_puttupleslot(tuplestorestate, outerslot);
(gdb) 
149            ExecCopySlot(slot, outerslot);
(gdb) 
150            return slot;
(gdb) p *slot
$18 = {type = T_TupleTableSlot, tts_flags = 20, tts_nvalid = 0, 
  tts_ops = 0xc3e720 <TTSOpsMinimalTuple>, tts_tupleDescriptor = 0x1230660, 
  tts_values = 0x12307e8, tts_isnull = 0x12307f0, tts_mcxt = 0x122fd70, tts_tid = {
    ip_blkid = {bi_hi = 65535, bi_lo = 65535}, ip_posid = 0}, tts_tableOid = 0}
(gdb) p *slot->tts_values
$19 = 0
(gdb)

继续执行

...
(gdb) p slot->tts_values[0]
$24 = 9998243
(gdb) c
Continuing.
Breakpoint 1, ExecMaterial (pstate=0x1230128) at nodeMaterial.c:41
41        MaterialState *node = castNode(MaterialState, pstate);
(gdb) n
49        CHECK_FOR_INTERRUPTS();
(gdb) 
54        estate = node->ss.ps.state;
(gdb) 
55        dir = estate->es_direction;
(gdb) 
56        forward = ScanDirectionIsForward(dir);
(gdb) 
57        tuplestorestate = node->tuplestorestate;
(gdb) 
62        if (tuplestorestate == NULL && node->eflags != 0)
(gdb) 
85        eof_tuplestore = (tuplestorestate == NULL) ||
(gdb) 
86            tuplestore_ateof(tuplestorestate);
(gdb) 
85        eof_tuplestore = (tuplestorestate == NULL) ||
(gdb) 
88        if (!forward && eof_tuplestore)
(gdb) 
107        slot = node->ss.ps.ps_ResultTupleSlot;
(gdb) 
108        if (!eof_tuplestore)
(gdb) 
124        if (eof_tuplestore && !node->eof_underlying)
(gdb) 
133            outerNode = outerPlanState(node);
(gdb) 
134            outerslot = ExecProcNode(outerNode);
(gdb) 
135            if (TupIsNull(outerslot))
(gdb) 
146            if (tuplestorestate)
(gdb) 
147                tuplestore_puttupleslot(tuplestorestate, outerslot);
(gdb) 
149            ExecCopySlot(slot, outerslot);
(gdb) 
150            return slot;
(gdb) p slot->tts_values[0]
$25 = 9998244
(gdb) 
...

DONE

四、参考资料

N/A

来自 “ ITPUB博客 ” ,链接:http://blog.itpub.net/6906/viewspace-2660377/,如需转载,请注明出处,否则将追究法律责任。

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