网站开发科普书,国产地图软件哪个好用,自用电脑做网站,微信推广的平台我们分析一下在PostgreSQL数据库中#xff0c;是如何实现除法操作的。其他的运算符操作与之类似。以下面的语句为例#xff1a;
select 2/4;源码分析
主流程如下#xff1a;
exec_simple_query
-- pg_parse_query
-- pg_analyze_and_rewrite
-- pg_plan_quer…我们分析一下在PostgreSQL数据库中是如何实现除法操作的。其他的运算符操作与之类似。以下面的语句为例
select 2/4;源码分析
主流程如下
exec_simple_query
-- pg_parse_query
-- pg_analyze_and_rewrite
-- pg_plan_queries
-- PortalStart
-- PortalRun
-- PortalDrop解析部分
exec_simple_query
-- pg_parse_query // 构造语法解析树SelectStmt--ResTarget--A_Expr-- raw_parser-- base_yyparse对select 2/4的语法解析部分比较简单。构造SelectStmt节点只存在target部分构造targetList字段 target为ResTarget在ResTarget中构造val字段为2/4的表达式节点表示A_Expr。在运算符的语法解析表示上gram.y中定义的源码如下
simple_select:SELECT opt_all_clause opt_target_listinto_clause from_clause where_clause group_clause having_clause window_clause{SelectStmt *n makeNode(SelectStmt);n-targetList $4;-- ...}
/******************************************************************************* target list for SELECT******************************************************************************/
opt_target_list: target_list { $$ $1; }| /* EMPTY */ { $$ NIL; };target_list:target_el { $$ list_make1($1); }| target_list , target_el { $$ lappend($1, $3); };
target_el: a_expr{$$ makeNode(ResTarget);$$-name NULL;$$-indirection NIL;$$-val (Node *)$1;$$-location 1;}
a_expr: c_expr { $$ $1; }/** These operators must be called out explicitly in order to make use* of bisons automatic operator-precedence handling. All other* operator names are handled by the generic productions using Op,* below; and all those operators will have the same precedence.** If you add more explicitly-known operators, be sure to add them* also to b_expr and to the MathOp list below.*/| a_expr %prec UMINUS{ $$ (Node *) makeSimpleA_Expr(AEXPR_OP, , NULL, $2, 1); }| - a_expr %prec UMINUS{ $$ doNegate($2, 1); }| a_expr a_expr{ $$ (Node *) makeSimpleA_Expr(AEXPR_OP, , $1, $3, 2); }| a_expr - a_expr{ $$ (Node *) makeSimpleA_Expr(AEXPR_OP, -, $1, $3, 2); }| a_expr * a_expr{ $$ (Node *) makeSimpleA_Expr(AEXPR_OP, *, $1, $3, 2); }| a_expr / a_expr{ $$ (Node *) makeSimpleA_Expr(AEXPR_OP, /, $1, $3, 2); }构造了一个A_Expr节点
/** makeSimpleA_Expr -* As above, given a simple (unqualified) operator name*/
A_Expr *makeSimpleA_Expr(A_Expr_Kind kind, char *name, Node *lexpr, Node *rexpr, int location)
{A_Expr *a makeNode(A_Expr);a-kind kind;a-name list_make1(makeString((char *) name));a-lexpr lexpr;a-rexpr rexpr;a-location location;return a;
}语义分析阶段
exec_simple_query
-- pg_parse_query
-- pg_analyze_and_rewrite-- parse_analyze-- transformStmt-- transformSelectStmt // transforms a Select Statement-- transformTargetList /* Turns a list of ResTargets into a list of TargetEntrys. */-- transformTargetEntry-- transformExpr-- transformAExprOp-- makeTargetEntry-- make_op // 构造操作符表达式Expr节点OpExpr-- oper // search for a binary operator、-- ket_ok make_oper_cache_key // 先在缓存中找, 找到返回-- DeconstructQualifiedName // 获取操作符name, namespace-- fetch_search_path_array-- recomputeNamespacePath();-- if (key_ok)-- find_oper_cache_entry -- binary_oper_exact // 如果缓存中没有找到-- OpernameGetOprid // 查找pg_operator系统表找-- enforce_generic_type_consistency-- make_fn_arguments
-- pg_plan_queries-- standard_planner-- subquery_planner-- pull_up_subqueries-- preprocess_expression// 化简常量表达式如果可以的话immutable才行-- eval_const_expressions-- set_opfuncid-- simplify_function-- expand_function_arguments-- evaluate_function // try to pre-evaluate a function call-- evaluate_expr // 预执行一个常量表达式-- CreateExecutorState-- ExecInitExpr-- ExecInitExprRec-- ExecInitFunc-- ExecReadyExpr-- ExecEvalExprSwitchContext // 执行获取一个常量值-- ExecInterpExpr-- int4div // 调用除法实现函数 计算结果-- makeConst // 将执行常量表达式获得的结果转换为Const常量节点返回-- grouping_planner-- query_planner-- build_simple_rel-- create_empty_pathtarget // 构造PathTarget-- create_group_result_path // 生成GroupResultPath-- apply_scanjoin_target_to_paths-- create_projection_path-- create_plan-- create_projection_plan-- create_group_result_plan
-- PortalStart-- ExecutorStart-- InitPlan-- ExecInitResult
-- PortalRun-- ExecutorRun-- standard_ExecutorRun-- ExecutePlan-- ExecResult-- ExecProject
-- PortalDrop在这个阶段会找到/除法操作符的oid即查系统表pg_operaotr在函数oper中我们下面查看一下系统表查询一下除法/操作符这个操作符你一定意义上可以认为是函数除法函数。需要输入参数输出结果。 PG文档10.2. 操作符 postgres# select * from pg_operator where oprname /;oid | oprname | oprnamespace | oprowner | oprkind | oprcanmerge | oprcanhash | oprleft | oprright | oprresult | oprcom | oprnegate | oprcode | oprrest | oprjoin
-----------------------------------------------------------------------------------------------------------------------------------------------------------527 | / | 11 | 10 | b | f | f | 21 | 21 | 21 | 0 | 0 | int2div | - | -528 | / | 11 | 10 | b | f | f | 23 | 23 | 23 | 0 | 0 | int4div | - | -546 | / | 11 | 10 | b | f | f | 21 | 23 | 23 | 0 | 0 | int24div | - | -547 | / | 11 | 10 | b | f | f | 23 | 21 | 23 | 0 | 0 | int42div | - | -588 | / | 11 | 10 | b | f | f | 700 | 700 | 700 | 0 | 0 | float4div | - | -593 | / | 11 | 10 | b | f | f | 701 | 701 | 701 | 0 | 0 | float8div | - | -687 | / | 11 | 10 | b | f | f | 20 | 20 | 20 | 0 | 0 | int8div | - | -691 | / | 11 | 10 | b | f | f | 20 | 23 | 20 | 0 | 0 | int84div | - | -695 | / | 11 | 10 | b | f | f | 23 | 20 | 20 | 0 | 0 | int48div | - | -821 | / | 11 | 10 | b | f | f | 20 | 21 | 20 | 0 | 0 | int82div | - | -825 | / | 11 | 10 | b | f | f | 21 | 20 | 20 | 0 | 0 | int28div | - | -734 | / | 11 | 10 | b | f | f | 600 | 600 | 600 | 0 | 0 | point_div | - | -739 | / | 11 | 10 | b | f | f | 602 | 600 | 602 | 0 | 0 | path_div_pt | - | -807 | / | 11 | 10 | b | f | f | 603 | 600 | 603 | 0 | 0 | box_div | - | -844 | / | 11 | 10 | b | f | f | 790 | 700 | 790 | 0 | 0 | cash_div_flt4 | - | -909 | / | 11 | 10 | b | f | f | 790 | 701 | 790 | 0 | 0 | cash_div_flt8 | - | -3347 | / | 11 | 10 | b | f | f | 790 | 20 | 790 | 0 | 0 | cash_div_int8 | - | -913 | / | 11 | 10 | b | f | f | 790 | 23 | 790 | 0 | 0 | cash_div_int4 | - | -915 | / | 11 | 10 | b | f | f | 790 | 21 | 790 | 0 | 0 | cash_div_int2 | - | -3825 | / | 11 | 10 | b | f | f | 790 | 790 | 701 | 0 | 0 | cash_div_cash | - | -1118 | / | 11 | 10 | b | f | f | 700 | 701 | 701 | 0 | 0 | float48div | - | -1128 | / | 11 | 10 | b | f | f | 701 | 700 | 701 | 0 | 0 | float84div | - | -1519 | / | 11 | 10 | b | f | f | 718 | 600 | 718 | 0 | 0 | circle_div_pt | - | -1585 | / | 11 | 10 | b | f | f | 1186 | 701 | 1186 | 0 | 0 | interval_div | - | -1761 | / | 11 | 10 | b | f | f | 1700 | 1700 | 1700 | 0 | 0 | numeric_div | - | -
(25 rows)
可以查到select 2/4;对应的是oid528,实现该操作符的函数是int4divoprcode表示实现该操作符的函数可通过查看系统表pg_proc查看该函数的详细信息
postgrespostgres# select * from pg_proc where pronameint4div;
-[ RECORD 1 ]-----------
oid | 154
proname | int4div -- 函数名
pronamespace | 11
proowner | 10
prolang | 12
procost | 1
prorows | 0
provariadic | 0
prosupport | -
prokind | f
prosecdef | f
proleakproof | f
proisstrict | t
proretset | f
provolatile | i
proparallel | s
pronargs | 2
pronargdefaults | 0
prorettype | 23 -- 返回参数
proargtypes | 23 23 -- 入参
proallargtypes |
proargmodes |
proargnames |
proargdefaults |
protrftypes |
prosrc | int4div -- 函数source
probin |
proconfig |
proacl | 其中除法表达式A_Expr经过语义分析后通过OpExpr进行表示
/** OpExpr - expression node for an operator invocation** Semantically, this is essentially the same as a function call.* 语义上等同于一个函数调用* Note that opfuncid is not necessarily filled in immediately on creation* of the node. The planner makes sure it is valid before passing the node* tree to the executor, but during parsing/planning opfuncid can be 0.*/
typedef struct OpExpr
{Expr xpr;Oid opno; /* PG_OPERATOR OID of the operator */ //对应pg_operator.oidOid opfuncid; /* PG_PROC OID of underlying function */ // 实现该操作符的函数oidOid opresulttype; /* PG_TYPE OID of result value */ // 返回值类型bool opretset; /* true if operator returns set */Oid opcollid; /* OID of collation of result */Oid inputcollid; /* OID of collation that operator should use */List *args; /* arguments to the operator (1 or 2) */ // 参数int location; /* token location, or -1 if unknown */
} OpExpr;
除法的实现函数
Datum int4div(PG_FUNCTION_ARGS)
{int32 arg1 PG_GETARG_INT32(0);int32 arg2 PG_GETARG_INT32(1);int32 result;if (arg2 0){ereport(ERROR,(errcode(ERRCODE_DIVISION_BY_ZERO),errmsg(division by zero)));/* ensure compiler realizes we mustnt reach the division (gcc bug) */PG_RETURN_NULL();}/** INT_MIN / -1 is problematic, since the result cant be represented on a* twos-complement machine. Some machines produce INT_MIN, some produce* zero, some throw an exception. We can dodge the problem by recognizing* that division by -1 is the same as negation.*/if (arg2 -1){if (unlikely(arg1 PG_INT32_MIN))ereport(ERROR,(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE), errmsg(integer out of range)));result -arg1;PG_RETURN_INT32(result);}/* No overflow is possible */result arg1 / arg2;PG_RETURN_INT32(result);
}从上面的分析过程来看其实运算符操作与调用一个函数是差不多的。基本可以认为是等同。
