PostgreSQL 原始碼解讀（49）- 查詢語句#34（make_one_rel函式#1-概覽）
先前的章節已介紹了函式query_planner中子函式create_lateral_join_info、match_foreign_keys_to_quals和extract_restriction_or_clauses的主要實現邏輯,本節介紹query_planner中主計劃函式make_one_rel的主實現邏輯。
query_planner程式碼片段:
//...
/*
* Ready to do the primary planning.
*/
final_rel = make_one_rel(root, joinlist);//執行主要的計劃過程
/* Check that we got at least one usable path */
if (!final_rel || !final_rel->cheapest_total_path ||
final_rel->cheapest_total_path->param_info != NULL)
elog(ERROR, "failed to construct the join relation");//檢查
return final_rel;//返回結果
//...
一、資料結構
RelOptInfo
typedef struct RelOptInfo
{
NodeTag type;//節點標識
RelOptKind reloptkind;//RelOpt型別
/* all relations included in this RelOptInfo */
Relids relids; /*Relids(rtindex)集合 set of base relids (rangetable indexes) */
/* size estimates generated by planner */
double rows; /*結果元組的估算數量 estimated number of result tuples */
/* per-relation planner control flags */
bool consider_startup; /*是否考慮啟動成本?是,需要保留啟動成本低的路徑 keep cheap-startup-cost paths? */
bool consider_param_startup; /*是否考慮引數化?的路徑 ditto, for parameterized paths? */
bool consider_parallel; /*是否考慮並行處理路徑 consider parallel paths? */
/* default result targetlist for Paths scanning this relation */
struct PathTarget *reltarget; /*掃描該Relation時預設的結果 list of Vars/Exprs, cost, width */
/* materialization information */
List *pathlist; /*訪問路徑連結串列 Path structures */
List *ppilist; /*路徑連結串列中使用引數化路徑進行 ParamPathInfos used in pathlist */
List *partial_pathlist; /* partial Paths */
struct Path *cheapest_startup_path;//代價最低的啟動路徑
struct Path *cheapest_total_path;//代價最低的整體路徑
struct Path *cheapest_unique_path;//代價最低的獲取唯一值的路徑
List *cheapest_parameterized_paths;//代價最低的引數化?路徑連結串列
/* parameterization information needed for both base rels and join rels */
/* (see also lateral_vars and lateral_referencers) */
Relids direct_lateral_relids; /*使用lateral語法,需依賴的Relids rels directly laterally referenced */
Relids lateral_relids; /* minimum parameterization of rel */
/* information about a base rel (not set for join rels!) */
//reloptkind=RELOPT_BASEREL時使用的資料結構
Index relid; /* Relation ID */
Oid reltablespace; /* 表空間 containing tablespace */
RTEKind rtekind; /* 基表?子查詢?還是函式等等?RELATION, SUBQUERY, FUNCTION, etc */
AttrNumber min_attr; /* 最小的屬性編號 smallest attrno of rel (often <0) */
AttrNumber max_attr; /* 最大的屬性編號 largest attrno of rel */
Relids *attr_needed; /* 陣列 array indexed [min_attr .. max_attr] */
int32 *attr_widths; /* 屬性寬度 array indexed [min_attr .. max_attr] */
List *lateral_vars; /* 關係依賴的Vars/PHVs LATERAL Vars and PHVs referenced by rel */
Relids lateral_referencers; /*依賴該關係的Relids rels that reference me laterally */
List *indexlist; /* 該關係的IndexOptInfo連結串列 list of IndexOptInfo */
List *statlist; /* 統計資訊連結串列 list of StatisticExtInfo */
BlockNumber pages; /* 塊數 size estimates derived from pg_class */
double tuples; /* 元組數 */
double allvisfrac; /* ? */
PlannerInfo *subroot; /* 如為子查詢,儲存子查詢的root if subquery */
List *subplan_params; /* 如為子查詢,儲存子查詢的引數 if subquery */
int rel_parallel_workers; /* 並行執行,需要多少個workers? wanted number of parallel workers */
/* Information about foreign tables and foreign joins */
//FWD相關資訊
Oid serverid; /* identifies server for the table or join */
Oid userid; /* identifies user to check access as */
bool useridiscurrent; /* join is only valid for current user */
/* use "struct FdwRoutine" to avoid including fdwapi.h here */
struct FdwRoutine *fdwroutine;
void *fdw_private;
/* cache space for remembering if we have proven this relation unique */
//已知的,可保證唯一的Relids連結串列
List *unique_for_rels; /* known unique for these other relid
* set(s) */
List *non_unique_for_rels; /* 已知的,不唯一的Relids連結串列 known not unique for these set(s) */
/* used by various scans and joins: */
List *baserestrictinfo; /* 如為基本關係,儲存約束條件 RestrictInfo structures (if base rel) */
QualCost baserestrictcost; /* 解析約束表示式的成本? cost of evaluating the above */
Index baserestrict_min_security; /* 最低安全等級 min security_level found in
* baserestrictinfo */
List *joininfo; /* 連線語句的約束條件資訊 RestrictInfo structures for join clauses
* involving this rel */
bool has_eclass_joins; /* 是否存在等價類連線? T means joininfo is incomplete */
/* used by partitionwise joins: */
bool consider_partitionwise_join; /* 分割槽? consider partitionwise
* join paths? (if
* partitioned rel) */
Relids top_parent_relids; /* Relids of topmost parents (if "other"
* rel) */
/* used for partitioned relations */
//分割槽表使用
PartitionScheme part_scheme; /* 分割槽的schema Partitioning scheme. */
int nparts; /* 分割槽數 number of partitions */
struct PartitionBoundInfoData *boundinfo; /* 分割槽邊界資訊 Partition bounds */
List *partition_qual; /* 分割槽約束 partition constraint */
struct RelOptInfo **part_rels; /* 分割槽的RelOptInfo陣列 Array of RelOptInfos of partitions,
* stored in the same order of bounds */
List **partexprs; /* 非空分割槽鍵表示式 Non-nullable partition key expressions. */
List **nullable_partexprs; /* 可為空的分割槽鍵表示式 Nullable partition key expressions. */
List *partitioned_child_rels; /* RT Indexes連結串列 List of RT indexes. */
} RelOptInfo;
二、原始碼解讀
make_one_rel
make_one_rel函式找出執行查詢的所有可能訪問路徑,但不考慮上層的Non-SPJ操作,返回一個最上層的RelOptInfo.
make_one_rel函式分為兩個階段:生成掃描路徑(set_base_rel_pathlists)和生成連線路徑(make_rel_from_joinlist).
注:SPJ是指選擇(Select)/投影(Project)/連線(Join),相對應的Non-SPJ操作是指Group分組/Sort排序等操作
/*
* make_one_rel
* Finds all possible access paths for executing a query, returning a
* single rel that represents the join of all base rels in the query.
*/
RelOptInfo *
make_one_rel(PlannerInfo *root, List *joinlist)
{
RelOptInfo *rel;
Index rti;
/*
* Construct the all_baserels Relids set.
*/
root->all_baserels = NULL;
for (rti = 1; rti < root->simple_rel_array_size; rti++)//遍歷RelOptInfo
{
RelOptInfo *brel = root->simple_rel_array[rti];
/* there may be empty slots corresponding to non-baserel RTEs */
if (brel == NULL)
continue;
Assert(brel->relid == rti); /* sanity check on array */
/* ignore RTEs that are "other rels" */
if (brel->reloptkind != RELOPT_BASEREL)
continue;
root->all_baserels = bms_add_member(root->all_baserels, brel->relid);//新增到all_baserels遍歷中
}
/* Mark base rels as to whether we care about fast-start plans */
//設定RelOptInfo的consider_param_startup變數,是否考量fast-start plans
set_base_rel_consider_startup(root);
/*
* Compute size estimates and consider_parallel flags for each base rel,
* then generate access paths.
*/
set_base_rel_sizes(root);//估算Relation的Size並且設定consider_parallel標記
set_base_rel_pathlists(root);//生成Relation的掃描(訪問)路徑
/*
* Generate access paths for the entire join tree.
* 透過動態規劃或遺傳演算法生成連線路徑
*/
rel = make_rel_from_joinlist(root, joinlist);
/*
* The result should join all and only the query's base rels.
*/
Assert(bms_equal(rel->relids, root->all_baserels));
//返回最上層的RelOptInfo
return rel;
}
//--------------------------------------------------------
/*
* set_base_rel_consider_startup
* Set the consider_[param_]startup flags for each base-relation entry.
*
* For the moment, we only deal with consider_param_startup here; because the
* logic for consider_startup is pretty trivial and is the same for every base
* relation, we just let build_simple_rel() initialize that flag correctly to
* start with. If that logic ever gets more complicated it would probably
* be better to move it here.
*/
static void
set_base_rel_consider_startup(PlannerInfo *root)
{
/*
* Since parameterized paths can only be used on the inside of a nestloop
* join plan, there is usually little value in considering fast-start
* plans for them. However, for relations that are on the RHS of a SEMI
* or ANTI join, a fast-start plan can be useful because we're only going
* to care about fetching one tuple anyway.
*
* To minimize growth of planning time, we currently restrict this to
* cases where the RHS is a single base relation, not a join; there is no
* provision for consider_param_startup to get set at all on joinrels.
* Also we don't worry about appendrels. costsize.c's costing rules for
* nestloop semi/antijoins don't consider such cases either.
*/
ListCell *lc;
foreach(lc, root->join_info_list)
{
SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc);
int varno;
if ((sjinfo->jointype == JOIN_SEMI || sjinfo->jointype == JOIN_ANTI) &&
bms_get_singleton_member(sjinfo->syn_righthand, &varno))
{
RelOptInfo *rel = find_base_rel(root, varno);
rel->consider_param_startup = true;
}
}
}
//--------------------------------------------------------
/*
* set_base_rel_sizes
* Set the size estimates (rows and widths) for each base-relation entry.
* Also determine whether to consider parallel paths for base relations.
*
* We do this in a separate pass over the base rels so that rowcount
* estimates are available for parameterized path generation, and also so
* that each rel's consider_parallel flag is set correctly before we begin to
* generate paths.
*/
static void
set_base_rel_sizes(PlannerInfo *root)
{
Index rti;
for (rti = 1; rti < root->simple_rel_array_size; rti++)//遍歷RelOptInfo陣列
{
RelOptInfo *rel = root->simple_rel_array[rti];
RangeTblEntry *rte;
/* there may be empty slots corresponding to non-baserel RTEs */
if (rel == NULL)
continue;
Assert(rel->relid == rti); /* sanity check on array */
/* ignore RTEs that are "other rels" */
if (rel->reloptkind != RELOPT_BASEREL)
continue;
rte = root->simple_rte_array[rti];
/*
* If parallelism is allowable for this query in general, see whether
* it's allowable for this rel in particular. We have to do this
* before set_rel_size(), because (a) if this rel is an inheritance
* parent, set_append_rel_size() will use and perhaps change the rel's
* consider_parallel flag, and (b) for some RTE types, set_rel_size()
* goes ahead and makes paths immediately.
*/
if (root->glob->parallelModeOK)
set_rel_consider_parallel(root, rel, rte);
set_rel_size(root, rel, rti, rte);
}
}
/*
* set_rel_size
* Set size estimates for a base relation
*/
static void
set_rel_size(PlannerInfo *root, RelOptInfo *rel,
Index rti, RangeTblEntry *rte)
{
if (rel->reloptkind == RELOPT_BASEREL &&
relation_excluded_by_constraints(root, rel, rte))
{
/*
* We proved we don't need to scan the rel via constraint exclusion,
* so set up a single dummy path for it. Here we only check this for
* regular baserels; if it's an otherrel, CE was already checked in
* set_append_rel_size().
*
* In this case, we go ahead and set up the relation's path right away
* instead of leaving it for set_rel_pathlist to do. This is because
* we don't have a convention for marking a rel as dummy except by
* assigning a dummy path to it.
*/
set_dummy_rel_pathlist(rel);//
}
else if (rte->inh)//inherit table
{
/* It's an "append relation", process accordingly */
set_append_rel_size(root, rel, rti, rte);
}
else
{
switch (rel->rtekind)
{
case RTE_RELATION://資料表
if (rte->relkind == RELKIND_FOREIGN_TABLE)//FDW
{
/* Foreign table */
set_foreign_size(root, rel, rte);
}
else if (rte->relkind == RELKIND_PARTITIONED_TABLE)//分割槽表
{
/*
* A partitioned table without any partitions is marked as
* a dummy rel.
*/
set_dummy_rel_pathlist(rel);
}
else if (rte->tablesample != NULL)//取樣表
{
/* Sampled relation */
set_tablesample_rel_size(root, rel, rte);
}
else
{
/* Plain relation */
set_plain_rel_size(root, rel, rte);//常規的資料表
}
break;
case RTE_SUBQUERY://子查詢
/*
* Subqueries don't support making a choice between
* parameterized and unparameterized paths, so just go ahead
* and build their paths immediately.
*/
set_subquery_pathlist(root, rel, rti, rte);//生成子查詢訪問路徑
break;
case RTE_FUNCTION://FUNCTION
set_function_size_estimates(root, rel);
break;
case RTE_TABLEFUNC://TABLEFUNC
set_tablefunc_size_estimates(root, rel);
break;
case RTE_VALUES://VALUES
set_values_size_estimates(root, rel);
break;
case RTE_CTE://CTE
/*
* CTEs don't support making a choice between parameterized
* and unparameterized paths, so just go ahead and build their
* paths immediately.
*/
if (rte->self_reference)
set_worktable_pathlist(root, rel, rte);
else
set_cte_pathlist(root, rel, rte);
break;
case RTE_NAMEDTUPLESTORE://NAMEDTUPLESTORE,命名元組儲存
set_namedtuplestore_pathlist(root, rel, rte);
break;
default:
elog(ERROR, "unexpected rtekind: %d", (int) rel->rtekind);
break;
}
}
/*
* We insist that all non-dummy rels have a nonzero rowcount estimate.
*/
Assert(rel->rows > 0 || IS_DUMMY_REL(rel));
}
//--------------------------------------------------------
/*
* set_base_rel_pathlists
* Finds all paths available for scanning each base-relation entry.
* Sequential scan and any available indices are considered.
* Each useful path is attached to its relation's 'pathlist' field.
*
* 為每一個base rels找出所有可用的訪問路徑(順序掃描和所有可用的索引都會考慮在內)
* 每一個可用的路徑都會新增到pathlist連結串列中
*
*/
static void
set_base_rel_pathlists(PlannerInfo *root)
{
Index rti;
for (rti = 1; rti < root->simple_rel_array_size; rti++)//遍歷RelOptInfo陣列
{
RelOptInfo *rel = root->simple_rel_array[rti];
/* there may be empty slots corresponding to non-baserel RTEs */
if (rel == NULL)
continue;
Assert(rel->relid == rti); /* sanity check on array */
/* ignore RTEs that are "other rels" */
if (rel->reloptkind != RELOPT_BASEREL)
continue;
set_rel_pathlist(root, rel, rti, root->simple_rte_array[rti]);
}
}
/*
* set_rel_pathlist
* Build access paths for a base relation
*/
static void
set_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
Index rti, RangeTblEntry *rte)
{
if (IS_DUMMY_REL(rel))
{
/* We already proved the relation empty, so nothing more to do */
}
else if (rte->inh)//inherit
{
/* It's an "append relation", process accordingly */
set_append_rel_pathlist(root, rel, rti, rte);
}
else//常規
{
switch (rel->rtekind)
{
case RTE_RELATION://資料表
if (rte->relkind == RELKIND_FOREIGN_TABLE)//FDW
{
/* Foreign table */
set_foreign_pathlist(root, rel, rte);
}
else if (rte->tablesample != NULL)//取樣表
{
/* Sampled relation */
set_tablesample_rel_pathlist(root, rel, rte);
}
else//常規資料表
{
/* Plain relation */
set_plain_rel_pathlist(root, rel, rte);
}
break;
case RTE_SUBQUERY://子查詢
/* Subquery --- 已在set_rel_size處理,fully handled during set_rel_size */
break;
case RTE_FUNCTION:
/* RangeFunction */
set_function_pathlist(root, rel, rte);
break;
case RTE_TABLEFUNC:
/* Table Function */
set_tablefunc_pathlist(root, rel, rte);
break;
case RTE_VALUES:
/* Values list */
set_values_pathlist(root, rel, rte);
break;
case RTE_CTE:
/* CTE reference --- fully handled during set_rel_size */
break;
case RTE_NAMEDTUPLESTORE:
/* tuplestore reference --- fully handled during set_rel_size */
break;
default:
elog(ERROR, "unexpected rtekind: %d", (int) rel->rtekind);
break;
}
}
/*
* If this is a baserel, we should normally consider gathering any partial
* paths we may have created for it.
*
* However, if this is an inheritance child, skip it. Otherwise, we could
* end up with a very large number of gather nodes, each trying to grab
* its own pool of workers. Instead, we'll consider gathering partial
* paths for the parent appendrel.
*
* Also, if this is the topmost scan/join rel (that is, the only baserel),
* we postpone this until the final scan/join targelist is available (see
* grouping_planner).
*/
if (rel->reloptkind == RELOPT_BASEREL &&
bms_membership(root->all_baserels) != BMS_SINGLETON)
generate_gather_paths(root, rel, false);
/*
* Allow a plugin to editorialize on the set of Paths for this base
* relation. It could add new paths (such as CustomPaths) by calling
* add_path(), or delete or modify paths added by the core code.
*/
if (set_rel_pathlist_hook)//鉤子函式
(*set_rel_pathlist_hook) (root, rel, rti, rte);
/* Now find the cheapest of the paths for this rel */
set_cheapest(rel);//找出代價最低的訪問路徑
#ifdef OPTIMIZER_DEBUG
debug_print_rel(root, rel);
#endif
}
//------------------------------------------------------------
/*
* make_rel_from_joinlist
* Build access paths using a "joinlist" to guide the join path search.
*
* 根據joinlist構建連線訪問路徑,joinlist是函式deconstruct_jointree函式的返回
*
* See comments for deconstruct_jointree() for definition of the joinlist
* data structure.
*/
static RelOptInfo *
make_rel_from_joinlist(PlannerInfo *root, List *joinlist)
{
int levels_needed;
List *initial_rels;
ListCell *jl;
/*
* Count the number of child joinlist nodes. This is the depth of the
* dynamic-programming algorithm we must employ to consider all ways of
* joining the child nodes.
*/
levels_needed = list_length(joinlist);//joinlist連結串列長度
if (levels_needed <= 0)
return NULL; /* nothing to do? */
/*
* Construct a list of rels corresponding to the child joinlist nodes.
* This may contain both base rels and rels constructed according to
* sub-joinlists.
*/
initial_rels = NIL;
foreach(jl, joinlist)//遍歷連結串列
{
Node *jlnode = (Node *) lfirst(jl);
RelOptInfo *thisrel;
if (IsA(jlnode, RangeTblRef))//RTR
{
int varno = ((RangeTblRef *) jlnode)->rtindex;
thisrel = find_base_rel(root, varno);
}
else if (IsA(jlnode, List))
{
/* Recurse to handle subproblem */
thisrel = make_rel_from_joinlist(root, (List *) jlnode);//遞迴呼叫
}
else
{
elog(ERROR, "unrecognized joinlist node type: %d",
(int) nodeTag(jlnode));
thisrel = NULL; /* keep compiler quiet */
}
initial_rels = lappend(initial_rels, thisrel);//加入初始化連結串列中
}
if (levels_needed == 1)
{
/*
* Single joinlist node, so we're done.
*/
return (RelOptInfo *) linitial(initial_rels);
}
else
{
/*
* Consider the different orders in which we could join the rels,
* using a plugin, GEQO, or the regular join search code.
*
* We put the initial_rels list into a PlannerInfo field because
* has_legal_joinclause() needs to look at it (ugly :-().
*/
root->initial_rels = initial_rels;
if (join_search_hook)//鉤子函式
return (*join_search_hook) (root, levels_needed, initial_rels);
else if (enable_geqo && levels_needed >= geqo_threshold)
return geqo(root, levels_needed, initial_rels);//透過遺傳演算法構建連線訪問路徑
else
return standard_join_search(root, levels_needed, initial_rels);//透過動態規劃演算法構建連線路徑
}
}
三、參考資料
allpaths.c
來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/6906/viewspace-2374862/，如需轉載，請註明出處，否則將追究法律責任。
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