上一小节介绍了函数query_planner对简单语句(SELECT 2+2;)的处理逻辑,本节介绍了函数query_planner函数除此之外的其他主处理逻辑。
一、重要的数据结构
在query_planner中,对root(PlannerInfo)结构进行初始化和处理,为后续的计划作准备.
PlannerInfo
/*----------
* PlannerInfo
* Per-query information for planning/optimization
*
* This struct is conventionally called "root" in all the planner routines.
* It holds links to all of the planner's working state, in addition to the
* original Query. Note that at present the planner extensively modifies
* the passed-in Query data structure; someday that should stop.
*----------
*/
struct AppendRelInfo;
typedef struct PlannerInfo
{
NodeTag type;//Node标识
Query *parse; /* 查询树,the Query being planned */
PlannerGlobal *glob; /* 当前的planner全局信息,global info for current planner run */
Index query_level; /* 查询层次,1标识最高层,1 at the outermost Query */
struct PlannerInfo *parent_root; /* 如为子计划,则这里存储父计划器指针,NULL标识最高层,NULL at outermost Query */
/*
* plan_params contains the expressions that this query level needs to
* make available to a lower query level that is currently being planned.
* outer_params contains the paramIds of PARAM_EXEC Params that outer
* query levels will make available to this query level.
*/
List *plan_params; /* list of PlannerParamItems, see below */
Bitmapset *outer_params;
/*
* simple_rel_array holds pointers to "base rels" and "other rels" (see
* comments for RelOptInfo for more info). It is indexed by rangetable
* index (so entry 0 is always wasted). Entries can be NULL when an RTE
* does not correspond to a base relation, such as a join RTE or an
* unreferenced view RTE; or if the RelOptInfo hasn't been made yet.
*/
/* RelOptInfo数组,存储"base rels",比如基表/子查询等.该数组与RTE的顺序一一对应,而且是从1开始,因此[0]无用 */
struct RelOptInfo **simple_rel_array; /* All 1-rel RelOptInfos */
int simple_rel_array_size; /* 数组大小,allocated size of array */
/*
* simple_rte_array is the same length as simple_rel_array and holds
* pointers to the associated rangetable entries. This lets us avoid
* rt_fetch(), which can be a bit slow once large inheritance sets have
* been expanded.
*/
RangeTblEntry **simple_rte_array; /* RTE数组,rangetable as an array */
/*
* append_rel_array is the same length as the above arrays, and holds
* pointers to the corresponding AppendRelInfo entry indexed by
* child_relid, or NULL if none. The array itself is not allocated if
* append_rel_list is empty.
*/
struct AppendRelInfo **append_rel_array;//先前已介绍,在处理集合操作如UNION ALL时使用
/*
* all_baserels is a Relids set of all base relids (but not "other"
* relids) in the query; that is, the Relids identifier of the final join
* we need to form. This is computed in make_one_rel, just before we
* start making Paths.
*/
Relids all_baserels;//"base rels"
/*
* nullable_baserels is a Relids set of base relids that are nullable by
* some outer join in the jointree; these are rels that are potentially
* nullable below the WHERE clause, SELECT targetlist, etc. This is
* computed in deconstruct_jointree.
*/
Relids nullable_baserels;//Nullable-side端的"base rels"
/*
* join_rel_list is a list of all join-relation RelOptInfos we have
* considered in this planning run. For small problems we just scan the
* list to do lookups, but when there are many join relations we build a
* hash table for faster lookups. The hash table is present and valid
* when join_rel_hash is not NULL. Note that we still maintain the list
* even when using the hash table for lookups; this simplifies life for
* GEQO.
*/
List *join_rel_list; /* 参与连接的Relation的RelOptInfo链表,list of join-relation RelOptInfos */
struct HTAB *join_rel_hash; /* 可加快链表访问的hash表,optional hashtable for join relations */
/*
* When doing a dynamic-programming-style join search, join_rel_level[k]
* is a list of all join-relation RelOptInfos of level k, and
* join_cur_level is the current level. New join-relation RelOptInfos are
* automatically added to the join_rel_level[join_cur_level] list.
* join_rel_level is NULL if not in use.
*/
List **join_rel_level; /* RelOptInfo指针链表数组,k层的join存储在[k]中,lists of join-relation RelOptInfos */
int join_cur_level; /* 当前的join层次,index of list being extended */
List *init_plans; /* 查询的初始化计划链表,init SubPlans for query */
List *cte_plan_ids; /* CTE子计划ID链表,per-CTE-item list of subplan IDs */
List *multiexpr_params; /* List of Lists of Params for MULTIEXPR
* subquery outputs */
List *eq_classes; /* 活动的等价类链表,list of active EquivalenceClasses */
List *canon_pathkeys; /* 规范化PathKey链表,list of "canonical" PathKeys */
List *left_join_clauses; /* 外连接约束条件链表(左),list of RestrictInfos for mergejoinable
* outer join clauses w/nonnullable var on
* left */
List *right_join_clauses; /* 外连接约束条件链表(右),list of RestrictInfos for mergejoinable
* outer join clauses w/nonnullable var on
* right */
List *full_join_clauses; /* 全连接约束条件链表,list of RestrictInfos for mergejoinable
* full join clauses */
List *join_info_list; /* 特殊连接信息链表,list of SpecialJoinInfos */
List *append_rel_list; /* AppendRelInfo链表,list of AppendRelInfos */
List *rowMarks; /* list of PlanRowMarks */
List *placeholder_list; /* PHI链表,list of PlaceHolderInfos */
List *fkey_list; /* 外键信息链表,list of ForeignKeyOptInfos */
List *query_pathkeys; /* uery_planner()要求的PathKeys,desired pathkeys for query_planner() */
List *group_pathkeys; /* groupClause pathkeys, if any */
List *window_pathkeys; /* pathkeys of bottom window, if any */
List *distinct_pathkeys; /* distinctClause pathkeys, if any */
List *sort_pathkeys; /* sortClause pathkeys, if any */
List *part_schemes; /* 已规范化的分区Schema,Canonicalised partition schemes used in the
* query. */
List *initial_rels; /* 尝试连接的RelOptInfo链表,RelOptInfos we are now trying to join */
/* Use fetch_upper_rel() to get any particular upper rel */
List *upper_rels[UPPERREL_FINAL + 1]; /* 上层的RelOptInfo链表, upper-rel RelOptInfos */
/* Result tlists chosen by grouping_planner for upper-stage processing */
struct PathTarget *upper_targets[UPPERREL_FINAL + 1];//
/*
* grouping_planner passes back its final processed targetlist here, for
* use in relabeling the topmost tlist of the finished Plan.
*/
List *processed_tlist;//最后需处理的投影列
/* Fields filled during create_plan() for use in setrefs.c */
AttrNumber *grouping_map; /* for GroupingFunc fixup */
List *minmax_aggs; /* List of MinMaxAggInfos */
MemoryContext planner_cxt; /* 内存上下文,context holding PlannerInfo */
double total_table_pages; /* 所有的pages,# of pages in all tables of query */
double tuple_fraction; /* query_planner输入参数:元组处理比例,tuple_fraction passed to query_planner */
double limit_tuples; /* query_planner输入参数:limit_tuples passed to query_planner */
Index qual_security_level; /* 表达式的最新安全等级,minimum security_level for quals */
/* Note: qual_security_level is zero if there are no securityQuals */
InheritanceKind inhTargetKind; /* indicates if the target relation is an
* inheritance child or partition or a
* partitioned table */
bool hasJoinRTEs; /* 存在RTE_JOIN的RTE,true if any RTEs are RTE_JOIN kind */
bool hasLateralRTEs; /* 存在标记为LATERAL的RTE,true if any RTEs are marked LATERAL */
bool hasDeletedRTEs; /* 存在已在jointree删除的RTE,true if any RTE was deleted from jointree */
bool hasHavingQual; /* 存在Having子句,true if havingQual was non-null */
bool hasPseudoConstantQuals; /* true if any RestrictInfo has
* pseudoconstant = true */
bool hasRecursion; /* 递归语句,true if planning a recursive WITH item */
/* These fields are used only when hasRecursion is true: */
int wt_param_id; /* PARAM_EXEC ID for the work table */
struct Path *non_recursive_path; /* a path for non-recursive term */
/* These fields are workspace for createplan.c */
Relids curOuterRels; /* outer rels above current node */
List *curOuterParams; /* not-yet-assigned NestLoopParams */
/* optional private data for join_search_hook, e.g., GEQO */
void *join_search_private;
/* Does this query modify any partition key columns? */
bool partColsUpdated;
} PlannerInfo;
二、源码解读
本节介绍query_planner的主流程以及setup_simple_rel_arrays和setup_append_rel_array两个子函数的实现逻辑.
query_planner
/*
* query_planner
* Generate a path (that is, a simplified plan) for a basic query,
* which may involve joins but not any fancier features.
*
* 为一个基本的查询(可能涉及连接)生成访问路径(也可以视为一个简化的计划).
*
* Since query_planner does not handle the toplevel processing (grouping,
* sorting, etc) it cannot select the best path by itself. Instead, it
* returns the RelOptInfo for the top level of joining, and the caller
* (grouping_planner) can choose among the surviving paths for the rel.
*
* query_planner不会处理顶层的处理过程(如最后的分组/排序等操作),因此,不能选择最优的访问路径
* 该函数会返回RelOptInfo给最高层的连接,grouping_planner可以在剩下的路径中进行选择
*
* root describes the query to plan
* tlist is the target list the query should produce
* (this is NOT necessarily root->parse->targetList!)
* qp_callback is a function to compute query_pathkeys once it's safe to do so
* qp_extra is optional extra data to pass to qp_callback
*
* root是计划信息/tlist是投影列
* qp_callback是计算query_pathkeys的函数/qp_extra是传递给qp_callback的函数
*
* Note: the PlannerInfo node also includes a query_pathkeys field, which
* tells query_planner the sort order that is desired in the final output
* plan. This value is *not* available at call time, but is computed by
* qp_callback once we have completed merging the query's equivalence classes.
* (We cannot construct canonical pathkeys until that's done.)
*/
RelOptInfo *
query_planner(PlannerInfo *root, List *tlist,
query_pathkeys_callback qp_callback, void *qp_extra)
{
Query *parse = root->parse;//查询树
List *joinlist;
RelOptInfo *final_rel;//结果
Index rti;//RTE的index
double total_pages;//总pages数
/*
* If the query has an empty join tree, then it's something easy like
* "SELECT 2+2;" or "INSERT ... VALUES()". Fall through quickly.
*/
if (parse->jointree->fromlist == NIL)//简单SQL,无FROM/WHERE语句
{
/* We need a dummy joinrel to describe the empty set of baserels */
final_rel = build_empty_join_rel(root);//创建返回结果
/*
* If query allows parallelism in general, check whether the quals are
* parallel-restricted. (We need not check final_rel->reltarget
* because it's empty at this point. Anything parallel-restricted in
* the query tlist will be dealt with later.)
*/
if (root->glob->parallelModeOK)//并行模式?
final_rel->consider_parallel =
is_parallel_safe(root, parse->jointree->quals);
/* The only path for it is a trivial Result path */
add_path(final_rel, (Path *)
create_result_path(root, final_rel,
final_rel->reltarget,
(List *) parse->jointree->quals));//添加访问路径
/* Select cheapest path (pretty easy in this case...) */
set_cheapest(final_rel);//选择最优的访问路径
/*
* We still are required to call qp_callback, in case it's something
* like "SELECT 2+2 ORDER BY 1".
*/
root->canon_pathkeys = NIL;
(*qp_callback) (root, qp_extra);//回调函数
return final_rel;//返回
}
/*
* Init planner lists to empty.
*
* NOTE: append_rel_list was set up by subquery_planner, so do not touch
* here.
*/
root->join_rel_list = NIL;//初始化PlannerInfo
root->join_rel_hash = NULL;
root->join_rel_level = NULL;
root->join_cur_level = 0;
root->canon_pathkeys = NIL;
root->left_join_clauses = NIL;
root->right_join_clauses = NIL;
root->full_join_clauses = NIL;
root->join_info_list = NIL;
root->placeholder_list = NIL;
root->fkey_list = NIL;
root->initial_rels = NIL;
/*
* Make a flattened version of the rangetable for faster access (this is
* OK because the rangetable won't change any more), and set up an empty
* array for indexing base relations.
*/
setup_simple_rel_arrays(root);//初始化PlannerInfo->simple_rel/rte_array&size
/*
* Populate append_rel_array with each AppendRelInfo to allow direct
* lookups by child relid.
*/
setup_append_rel_array(root);//初始化PlannerInfo->append_rel_array(通过append_rel_list)
/*
* Construct RelOptInfo nodes for all base relations in query, and
* indirectly for all appendrel member relations ("other rels"). This
* will give us a RelOptInfo for every "simple" (non-join) rel involved in
* the query.
*
* Note: the reason we find the rels by searching the jointree and
* appendrel list, rather than just scanning the rangetable, is that the
* rangetable may contain RTEs for rels not actively part of the query,
* for example views. We don't want to make RelOptInfos for them.
*/
add_base_rels_to_query(root, (Node *) parse->jointree);//构建RelOptInfo节点
/*
* Examine the targetlist and join tree, adding entries to baserel
* targetlists for all referenced Vars, and generating PlaceHolderInfo
* entries for all referenced PlaceHolderVars. Restrict and join clauses
* are added to appropriate lists belonging to the mentioned relations. We
* also build EquivalenceClasses for provably equivalent expressions. The
* SpecialJoinInfo list is also built to hold information about join order
* restrictions. Finally, we form a target joinlist for make_one_rel() to
* work from.
*/
build_base_rel_tlists(root, tlist);//构建"base rels"的投影列
find_placeholders_in_jointree(root);//处理jointree中的PHI
find_lateral_references(root);//处理jointree中Lateral依赖
joinlist = deconstruct_jointree(root);//重构jointree
/*
* Reconsider any postponed outer-join quals now that we have built up
* equivalence classes. (This could result in further additions or
* mergings of classes.)
*/
reconsider_outer_join_clauses(root);//已创建等价类,那么需要重新考虑被推后处理的外连接表达式
/*
* If we formed any equivalence classes, generate additional restriction
* clauses as appropriate. (Implied join clauses are formed on-the-fly
* later.)
*/
generate_base_implied_equalities(root);//等价类构建后,生成因此外加的约束语句
/*
* We have completed merging equivalence sets, so it's now possible to
* generate pathkeys in canonical form; so compute query_pathkeys and
* other pathkeys fields in PlannerInfo.
*/
(*qp_callback) (root, qp_extra);//调用回调函数
/*
* Examine any "placeholder" expressions generated during subquery pullup.
* Make sure that the Vars they need are marked as needed at the relevant
* join level. This must be done before join removal because it might
* cause Vars or placeholders to be needed above a join when they weren't
* so marked before.
*/
fix_placeholder_input_needed_levels(root);//检查在子查询上拉时生成的PH表达式,确保Vars是OK的
/*
* Remove any useless outer joins. Ideally this would be done during
* jointree preprocessing, but the necessary information isn't available
* until we've built baserel data structures and classified qual clauses.
*/
joinlist = remove_useless_joins(root, joinlist);//清除无用的外连接
/*
* Also, reduce any semijoins with unique inner rels to plain inner joins.
* Likewise, this can't be done until now for lack of needed info.
*/
reduce_unique_semijoins(root);//消除半连接
/*
* Now distribute "placeholders" to base rels as needed. This has to be
* done after join removal because removal could change whether a
* placeholder is evaluable at a base rel.
*/
add_placeholders_to_base_rels(root);//在"base rels"中添加PH
/*
* Construct the lateral reference sets now that we have finalized
* PlaceHolderVar eval levels.
*/
create_lateral_join_info(root);//创建Lateral连接信息
/*
* Match foreign keys to equivalence classes and join quals. This must be
* done after finalizing equivalence classes, and it's useful to wait till
* after join removal so that we can skip processing foreign keys
* involving removed relations.
*/
match_foreign_keys_to_quals(root);//匹配外键信息
/*
* Look for join OR clauses that we can extract single-relation
* restriction OR clauses from.
*/
extract_restriction_or_clauses(root);//在OR语句中抽取约束条件
/*
* We should now have size estimates for every actual table involved in
* the query, and we also know which if any have been deleted from the
* query by join removal; so we can compute total_table_pages.
*
* Note that appendrels are not double-counted here, even though we don't
* bother to distinguish RelOptInfos for appendrel parents, because the
* parents will still have size zero.
*
* XXX if a table is self-joined, we will count it once per appearance,
* which perhaps is the wrong thing ... but that's not completely clear,
* and detecting self-joins here is difficult, so ignore it for now.
*/
total_pages = 0;
for (rti = 1; rti < root->simple_rel_array_size; rti++)//计算总pages
{
RelOptInfo *brel = root->simple_rel_array[rti];
if (brel == NULL)
continue;
Assert(brel->relid == rti); /* sanity check on array */
if (IS_SIMPLE_REL(brel))
total_pages += (double) brel->pages;
}
root->total_table_pages = total_pages;//赋值
/*
* Ready to do the primary planning.
*/
final_rel = make_one_rel(root, joinlist);//执行主要的计划过程
/* 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");//检查
return final_rel;//返回结果
}
setup_simple_rel_arrays
初始化setup_simple_rel_arrays(注意:[0]无用)和setup_simple_rel_arrays
/*
* setup_simple_rel_arrays
* Prepare the arrays we use for quickly accessing base relations.
*/
void
setup_simple_rel_arrays(PlannerInfo *root)
{
Index rti;
ListCell *lc;
/* Arrays are accessed using RT indexes (1..N) */
root->simple_rel_array_size = list_length(root->parse->rtable) + 1;
/* simple_rel_array is initialized to all NULLs */
root->simple_rel_array = (RelOptInfo **)
palloc0(root->simple_rel_array_size * sizeof(RelOptInfo *));
/* simple_rte_array is an array equivalent of the rtable list */
root->simple_rte_array = (RangeTblEntry **)
palloc0(root->simple_rel_array_size * sizeof(RangeTblEntry *));
rti = 1;
foreach(lc, root->parse->rtable)
{
RangeTblEntry *rte = (RangeTblEntry *) lfirst(lc);
root->simple_rte_array[rti++] = rte;
}
}
setup_append_rel_array
源码比较简单,读取append_rel_list中的信息初始化append_rel_array
/*
* setup_append_rel_array
* Populate the append_rel_array to allow direct lookups of
* AppendRelInfos by child relid.
*
* The array remains unallocated if there are no AppendRelInfos.
*/
void
setup_append_rel_array(PlannerInfo *root)
{
ListCell *lc;
int size = list_length(root->parse->rtable) + 1;
if (root->append_rel_list == NIL)
{
root->append_rel_array = NULL;
return;
}
root->append_rel_array = (AppendRelInfo **)
palloc0(size * sizeof(AppendRelInfo *));
foreach(lc, root->append_rel_list)
{
AppendRelInfo *appinfo = lfirst_node(AppendRelInfo, lc);
int child_relid = appinfo->child_relid;
/* Sanity check */
Assert(child_relid < size);
if (root->append_rel_array[child_relid])
elog(ERROR, "child relation already exists");
root->append_rel_array[child_relid] = appinfo;
}
}
