PostgreSQL 源码解读（44）- 查询语句#29（等价类
2018-09-16 本文已影响9人
EthanHe
上一小节介绍了函数query_planner中子函数deconstruct_jointree的主要实现逻辑,调用该函数后,PlannerInfo中生成等价类的相关信息,本节结合实际的内存数据介绍相关数据结构。
一、数据结构
/*
* EquivalenceClasses
*
* Whenever we can determine that a mergejoinable equality clause A = B is
* not delayed by any outer join, we create an EquivalenceClass containing
* the expressions A and B to record this knowledge. If we later find another
* equivalence B = C, we add C to the existing EquivalenceClass; this may
* require merging two existing EquivalenceClasses. At the end of the qual
* distribution process, we have sets of values that are known all transitively
* equal to each other, where "equal" is according to the rules of the btree
* operator family(s) shown in ec_opfamilies, as well as the collation shown
* by ec_collation. (We restrict an EC to contain only equalities whose
* operators belong to the same set of opfamilies. This could probably be
* relaxed, but for now it's not worth the trouble, since nearly all equality
* operators belong to only one btree opclass anyway. Similarly, we suppose
* that all or none of the input datatypes are collatable, so that a single
* collation value is sufficient.)
*
* We also use EquivalenceClasses as the base structure for PathKeys, letting
* us represent knowledge about different sort orderings being equivalent.
* Since every PathKey must reference an EquivalenceClass, we will end up
* with single-member EquivalenceClasses whenever a sort key expression has
* not been equivalenced to anything else. It is also possible that such an
* EquivalenceClass will contain a volatile expression ("ORDER BY random()"),
* which is a case that can't arise otherwise since clauses containing
* volatile functions are never considered mergejoinable. We mark such
* EquivalenceClasses specially to prevent them from being merged with
* ordinary EquivalenceClasses. Also, for volatile expressions we have
* to be careful to match the EquivalenceClass to the correct targetlist
* entry: consider SELECT random() AS a, random() AS b ... ORDER BY b,a.
* So we record the SortGroupRef of the originating sort clause.
*
* We allow equality clauses appearing below the nullable side of an outer join
* to form EquivalenceClasses, but these have a slightly different meaning:
* the included values might be all NULL rather than all the same non-null
* values. See src/backend/optimizer/README for more on that point.
*
* NB: if ec_merged isn't NULL, this class has been merged into another, and
* should be ignored in favor of using the pointed-to class.
*/
typedef struct EquivalenceClass
{
NodeTag type;
List *ec_opfamilies; /* btree操作符族(pg_opfamily)Oids,btree operator family OIDs */
Oid ec_collation; /* 主要用于排序的规则,collation, if datatypes are collatable */
List *ec_members; /* 等价类成员链表,list of EquivalenceMembers */
List *ec_sources; /* 产生等价类的RestrictInfo链表,list of generating RestrictInfos */
List *ec_derives; /* 衍生的RestrictInfo链表,list of derived RestrictInfos */
Relids ec_relids; /* 出现在成员中的所有relids,all relids appearing in ec_members, except
* for child members (see below) */
bool ec_has_const; /* 成员中是否存在常量?any pseudoconstants in ec_members? */
bool ec_has_volatile; /* 成员中是否存在易变表达式(如Random等),the (sole) member is a volatile expr */
bool ec_below_outer_join; /* 等价类是否应用于外连接下层?equivalence applies below an OJ */
bool ec_broken; /* 产生所需要的子句是否失败?failed to generate needed clauses? */
Index ec_sortref; /* 源于排序子句的标志,originating sortclause label, or 0 */
Index ec_min_security; /* 最小安全等级,minimum security_level in ec_sources */
Index ec_max_security; /* 最大安全等级,maximum security_level in ec_sources */
struct EquivalenceClass *ec_merged; /* 合并后的等价类,set if merged into another EC */
} EquivalenceClass;
/*
* If an EC contains a const and isn't below-outer-join, any PathKey depending
* on it must be redundant, since there's only one possible value of the key.
*/
#define EC_MUST_BE_REDUNDANT(eclass) \
((eclass)->ec_has_const && !(eclass)->ec_below_outer_join)
/*
* EquivalenceMember - one member expression of an EquivalenceClass
*
* em_is_child signifies that this element was built by transposing a member
* for an appendrel parent relation to represent the corresponding expression
* for an appendrel child. These members are used for determining the
* pathkeys of scans on the child relation and for explicitly sorting the
* child when necessary to build a MergeAppend path for the whole appendrel
* tree. An em_is_child member has no impact on the properties of the EC as a
* whole; in particular the EC's ec_relids field does NOT include the child
* relation. An em_is_child member should never be marked em_is_const nor
* cause ec_has_const or ec_has_volatile to be set, either. Thus, em_is_child
* members are not really full-fledged members of the EC, but just reflections
* or doppelgangers of real members. Most operations on EquivalenceClasses
* should ignore em_is_child members, and those that don't should test
* em_relids to make sure they only consider relevant members.
*
* em_datatype is usually the same as exprType(em_expr), but can be
* different when dealing with a binary-compatible opfamily; in particular
* anyarray_ops would never work without this. Use em_datatype when
* looking up a specific btree operator to work with this expression.
*/
typedef struct EquivalenceMember
{
NodeTag type;
Expr *em_expr; /* 该成员所代表的表达式,the expression represented */
Relids em_relids; /* 出现在表达式中的relids,all relids appearing in em_expr */
Relids em_nullable_relids; /* 低层外连接nullable端的relids,nullable by lower outer joins */
bool em_is_const; /* 常量?expression is pseudoconstant? */
bool em_is_child; /* 子Relation的衍生版本?derived version for a child relation? */
Oid em_datatype; /* 操作族使用到的数据类型,the "nominal type" used by the opfamily */
} EquivalenceMember;
二、跟踪分析
启动gdb,跟踪:
(gdb) b query_planner
Breakpoint 3 at 0x7693b5: file planmain.c, line 57.
执行函数deconstruct_jointree,查看root结构
156 joinlist = deconstruct_jointree(root);
(gdb)
163 reconsider_outer_join_clauses(root);
(gdb) p *root
$4 = {type = T_PlannerInfo, parse = 0x2c53ad0, glob = 0x2c8bff8, query_level = 1, parent_root = 0x0, plan_params = 0x0,
outer_params = 0x0, simple_rel_array = 0x2c941f8, simple_rel_array_size = 6, simple_rte_array = 0x2c94248,
all_baserels = 0x0, nullable_baserels = 0x0, join_rel_list = 0x0, join_rel_hash = 0x0, join_rel_level = 0x0,
join_cur_level = 0, init_plans = 0x0, cte_plan_ids = 0x0, multiexpr_params = 0x0, eq_classes = 0x2c960b8,
canon_pathkeys = 0x0, left_join_clauses = 0x0, right_join_clauses = 0x0, full_join_clauses = 0x0, join_info_list = 0x0,
append_rel_list = 0x0, rowMarks = 0x0, placeholder_list = 0x0, fkey_list = 0x0, query_pathkeys = 0x0,
group_pathkeys = 0x0, window_pathkeys = 0x0, distinct_pathkeys = 0x0, sort_pathkeys = 0x0, part_schemes = 0x0,
initial_rels = 0x0, upper_rels = {0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}, upper_targets = {0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0}, processed_tlist = 0x2c8e3d0, grouping_map = 0x0, minmax_aggs = 0x0, planner_cxt = 0x2b9fde0,
total_table_pages = 0, tuple_fraction = 0, limit_tuples = -1, qual_security_level = 0, inhTargetKind = INHKIND_NONE,
hasJoinRTEs = true, hasLateralRTEs = true, hasDeletedRTEs = false, hasHavingQual = false, hasPseudoConstantQuals = false,
hasRecursion = false, wt_param_id = -1, non_recursive_path = 0x0, curOuterRels = 0x0, curOuterParams = 0x0,
join_search_private = 0x0, partColsUpdated = false}
root->eq_classes是等价类链表,其中的元素是等价类
(gdb) p *root->eq_classes
$1 = {type = T_List, length = 2, head = 0x2c6daf8, tail = 0x2c6ddf8}
(gdb) set $ec1=(EquivalenceClass *)root->eq_classes->head->data.ptr_value
(gdb) set $ec2=(EquivalenceClass *)root->eq_classes->head->next->data.ptr_value
(gdb) p *$ec1
$4 = {type = T_EquivalenceClass, ec_opfamilies = 0x2c6d980, ec_collation = 100, ec_members = 0x2c6da58,
ec_sources = 0x2c6d9f0, ec_derives = 0x0, ec_relids = 0x2c6da20, ec_has_const = false, ec_has_volatile = false,
ec_below_outer_join = false, ec_broken = false, ec_sortref = 0, ec_min_security = 0, ec_max_security = 0, ec_merged = 0x0}
(gdb) p *$ec2
$5 = {type = T_EquivalenceClass, ec_opfamilies = 0x2c6dc30, ec_collation = 100, ec_members = 0x2c6dd58,
ec_sources = 0x2c6dca0, ec_derives = 0x0, ec_relids = 0x2c6dd20, ec_has_const = true, ec_has_volatile = false,
ec_below_outer_join = false, ec_broken = false, ec_sortref = 0, ec_min_security = 0, ec_max_security = 0, ec_merged = 0x0}
(gdb)
第1个等价类信息
ec_opfamilies
(gdb) p *$ec1->ec_opfamilies
$6 = {type = T_OidList, length = 2, head = 0x2c6d960, tail = 0x2c6d9b0}
(gdb) p $ec1->ec_opfamilies->head->data.oid_value
$7 = 1994
(gdb) p $ec1->ec_opfamilies->head->next->data.oid_value
$8 = 2095
(gdb)
数据字典中相应的记录:
testdb=# select * from pg_opfamily where oid=2095;
opfmethod | opfname | opfnamespace | opfowner
-----------+------------------+--------------+----------
403 | text_pattern_ops | 11 | 10
(1 row)
testdb=# select * from pg_opfamily where oid=1994;
opfmethod | opfname | opfnamespace | opfowner
-----------+----------+--------------+----------
403 | text_ops | 11 | 10
(1 row)
ec_members,共有2个元素
第1个元素,是rtindex=3的RTE,属性编号为2的字段,即t_grxx.grbh
(gdb) p *$ec1->ec_members
$10 = {type = T_List, length = 2, head = 0x2c6da38, tail = 0x2c6dad8}
(gdb) set $ec1_em1=(EquivalenceMember *)$ec1->ec_members->head->data.ptr_value
(gdb) set $ec1_em2=(EquivalenceMember *)$ec1->ec_members->head->next->data.ptr_value
(gdb) p *$ec1_em1
$13 = {type = T_EquivalenceMember, em_expr = 0x2c69f88, em_relids = 0x2c6d770, em_nullable_relids = 0x0,
em_is_const = false, em_is_child = false, em_datatype = 25}
(gdb) p *$ec1_em1
$13 = {type = T_EquivalenceMember, em_expr = 0x2c69f88, em_relids = 0x2c6d770, em_nullable_relids = 0x0,
em_is_const = false, em_is_child = false, em_datatype = 25}
(gdb) p *$ec1_em1->em_expr
$14 = {type = T_RelabelType}
(gdb) p *(RelabelType *)$ec1_em1->em_expr
$15 = {xpr = {type = T_RelabelType}, arg = 0x2c69f38, resulttype = 25, resulttypmod = -1, resultcollid = 100,
relabelformat = COERCE_IMPLICIT_CAST, location = -1}
(gdb) p *((RelabelType *)$ec1_em1->em_expr)->arg
$16 = {type = T_Var}
(gdb) p *(Var *)((RelabelType *)$ec1_em1->em_expr)->arg
$17 = {xpr = {type = T_Var}, varno = 3, varattno = 2, vartype = 1043, vartypmod = 14, varcollid = 100, varlevelsup = 0,
varnoold = 3, varoattno = 2, location = 136}
第2个元素,是rtindex=4的RTE,属性编号为1的字段,即t_jfxx.grbh
(gdb) p *$ec1_em2->em_expr
$28 = {type = T_RelabelType}
(gdb) p *(RelabelType *)$ec1_em2->em_expr
$29 = {xpr = {type = T_RelabelType}, arg = 0x2c69fd8, resulttype = 25, resulttypmod = -1, resultcollid = 100,
relabelformat = COERCE_IMPLICIT_CAST, location = -1}
(gdb) p *((RelabelType *)$ec1_em2->em_expr)->arg
$30 = {type = T_Var}
(gdb) p *(Var *)((RelabelType *)$ec1_em2->em_expr)->arg
$31 = {xpr = {type = T_Var}, varno = 4, varattno = 1, vartype = 1043, vartypmod = 14, varcollid = 100, varlevelsup = 0,
varnoold = 4, varoattno = 1, location = 146}
其他信息
(gdb) p *$ec1->ec_sources
$34 = {type = T_List, length = 1, head = 0x2c6d9d0, tail = 0x2c6d9d0}
(gdb) p *(Node *)$ec1->ec_sources->head->data.ptr_value
$35 = {type = T_RestrictInfo}
(gdb) p *(RestrictInfo *)$ec1->ec_sources->head->data.ptr_value
$36 = {type = T_RestrictInfo, clause = 0x2c6a098, is_pushed_down = true, outerjoin_delayed = false, can_join = true,
pseudoconstant = false, leakproof = false, security_level = 0, clause_relids = 0x2c6d7a0, required_relids = 0x2c6d758,
outer_relids = 0x0, nullable_relids = 0x0, left_relids = 0x2c6d770, right_relids = 0x2c6d788, orclause = 0x0,
parent_ec = 0x0, eval_cost = {startup = -1, per_tuple = 0}, norm_selec = -1, outer_selec = -1,
mergeopfamilies = 0x2c6d980, left_ec = 0x2c6ce68, right_ec = 0x2c6ce68, left_em = 0x2c6d890, right_em = 0x2c6da88,
scansel_cache = 0x0, outer_is_left = false, hashjoinoperator = 0, left_bucketsize = -1, right_bucketsize = -1,
left_mcvfreq = -1, right_mcvfreq = -1}
(gdb) p *$ec1->ec_relids
$38 = {nwords = 1, words = 0x2c6da24}
#即3号和4号RTE
(gdb) p $ec1->ec_relids->words[0]
$39 = 24
第2个等价类信息
(gdb) p *$ec2
$41 = {type = T_EquivalenceClass, ec_opfamilies = 0x2c6dc30, ec_collation = 100, ec_members = 0x2c6dd58,
ec_sources = 0x2c6dca0, ec_derives = 0x0, ec_relids = 0x2c6dd20, ec_has_const = true, ec_has_volatile = false,
ec_below_outer_join = false, ec_broken = false, ec_sortref = 0, ec_min_security = 0, ec_max_security = 0, ec_merged = 0x0}
ec_opfamilies,与第1个等价类的信息一致
(gdb) p *$ec2->ec_opfamilies
$42 = {type = T_OidList, length = 2, head = 0x2c6dc60, tail = 0x2c6dc10}
(gdb) p $ec2->ec_opfamilies->head->data.oid_value
$43 = 1994
(gdb) p $ec2->ec_opfamilies->head->next->data.oid_value
$44 = 2095
ec_members,有3个元素
(gdb) p *$ec2->ec_members
$46 = {type = T_List, length = 3, head = 0x2c6dd38, tail = 0x2c6df20}
(gdb) set $ec2_em1=(EquivalenceMember *)$ec2->ec_members->head->data.ptr_value
(gdb) set $ec2_em2=(EquivalenceMember *)$ec2->ec_members->head->next->data.ptr_value
(gdb) set $ec2_em3=(EquivalenceMember *)$ec2->ec_members->head->next->next->data.ptr_value
第1个元素,3号RTE,属性编号为1的字段,即t_grxx.dwbh
(gdb) p *$ec2_em1
$47 = {type = T_EquivalenceMember, em_expr = 0x2c69d58, em_relids = 0x2c6dbc8, em_nullable_relids = 0x0,
em_is_const = false, em_is_child = false, em_datatype = 25}
(gdb) p *$ec2_em1->em_expr
$48 = {type = T_RelabelType}
(gdb) p *(RelabelType *)$ec2_em1->em_expr
$49 = {xpr = {type = T_RelabelType}, arg = 0x2c69d08, resulttype = 25, resulttypmod = -1, resultcollid = 100,
relabelformat = COERCE_IMPLICIT_CAST, location = -1}
(gdb) p *(Var *)((RelabelType *)$ec2_em1->em_expr)->arg
$50 = {xpr = {type = T_Var}, varno = 3, varattno = 1, vartype = 1043, vartypmod = 14, varcollid = 100, varlevelsup = 0,
varnoold = 3, varoattno = 1, location = 115}
第2个元素
(gdb) p *$ec2_em2,1号RTE,属性编号为2的字段,即t_dwxx.dwbh
$52 = {type = T_EquivalenceMember, em_expr = 0x2c69e28, em_relids = 0x2c6dbe0, em_nullable_relids = 0x0,
em_is_const = false, em_is_child = false, em_datatype = 25}
(gdb) p *$ec2_em2->em_expr
$53 = {type = T_RelabelType}
(gdb) p *(Var *)((RelabelType *)$ec2_em2->em_expr)->arg
$54 = {xpr = {type = T_Var}, varno = 1, varattno = 2, vartype = 1043, vartypmod = 14, varcollid = 100, varlevelsup = 0,
varnoold = 1, varoattno = 2, location = 125}
第3个元素,是一个常量,即'1001'
(gdb) p *$ec2_em3
$55 = {type = T_EquivalenceMember, em_expr = 0x2c6a498, em_relids = 0x0, em_nullable_relids = 0x0, em_is_const = true,
em_is_child = false, em_datatype = 25}
(gdb) p *$ec2_em3->em_expr
$56 = {type = T_Const}
(gdb) p *((Const *)$ec2_em2->em_expr)->arg
(gdb) p *(Const *)$ec2_em3->em_expr
$58 = {xpr = {type = T_Const}, consttype = 25, consttypmod = -1, constcollid = 100, constlen = -1, constvalue = 46517720,
constisnull = false, constbyval = false, location = 172}
