PostgreSQL源码分析(2)– 常用数据类型/SQL语句的解释和执行

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POSTGResql源码分析(2)– 常用数据类型/sql语句的解释和执行
出处： http://www.loveopensource.com/?p=27 主要分析文件： // basic nodes deFinition src/include/nodes/nodes.h // sql parsed struct src/include/nodes/parsenodes.h // List定义 src/include/nodes/pg_List.h // List实现 src/BACkend/nodes/List.c // POSTGRes运行入口文件 src/BACkend/tcop/POSTGRes.c // utility Stmt运行文件 src/BACkend/tcop/utility.c // sql analyze and rewrite src/BACkend/parser/analyze.c POSTGResql用一种非常简单的形式实现了类似C++的继承,请看nodes.h ： typedef struct Node { NodeTagtype; } Node; 然后请看:parsenodes.h(sql语句经过parser解析后都先对应该该文件的一个struct中) 假设有一个create table的sql: create table test (name varchar(100,pass varchar(100)); 将会被解析到如下structure: typedef struct CreateStmt { NodeTagtype; RangeVar *relation;/* relation to create */ List *tableElts;/* column deFinitions (List of columnDef) */ List *inhRelations; /* relations to inherit from (List of * inhRelation) */ List *consTraints; /* consTraints (List of Constraint nodes) */ List *options;/* options from WITH clause */ OnCommitaction oncommit; /* @R_262_10112@ do we do at COMMIT? */ char *tablespacename; /* table space to use,or NulL */ } CreateStmt; 首先，看看该struct的第一个元素：type是一个NodeTag类型。 PG的很多struct的第一个元素都是NodeTag，这样在函数中传递指针变量时，他可以很 简单的把参数设置成：Node* 说简单点，其实有点像是所有的struct都继承了Node这个struct. 就是因为这个原因，看PG的代码很累，很多函数的参数和返回值都是一个简单的Node. 在Nodes.h中有每个Node的值的定义,比如：上面说的CreateStmt的type的值就是：T_CreateStmt 然后，PG中大量的使用了链表类型:List 在pg_List.h中有定义： typedef struct List { NodeTagtype; /* T_List,T_IntList,or T_OIDList */ int length; ListCell *head; ListCell *tail; } List; 可以看到，List的定义是基于基类Node来进行的。 常用的List操作函数有： //取List第一个元素 ListCell *y = List_head(List *l); //得到List的元素个数 List_length(List *l); // 遍历List foreach(cell,l) { … } 其他的很多函数具体可以参考pg_List.h和List.c 下面接着说sql的解释和执行。 所有的sql都会先解析成一个与之相对应的struct. SELEct会解析到: typedef struct SELEctStmt { NodeTagtype; /* * these fIElds are used only in “leaf” SELEctStmts. * * into,intoColnames,intoOptions,intoOnCommit,and in@R_531_10586@bleSpacename * are a kluge; they belong somewhere else… */ List *disTinctClause; /* NulL,List of disTinCT ON exprs,or * lcons(NIL,NIL) for all (SELECT disTinCT) */ RangeVar *into; /* target table (for SELEct into tablE) */ List *intoColnames; /* column names for into table */ List *intoOptions; /* options from WITH clause */ OnCommitaction intoOnCommit; /* @R_262_10112@ do we do at COMMIT? */ char *in@R_531_10586@bleSpacename;/* table space to use,or NulL */ List *targetList;/* the target List (of ResTarget) */ List *fromClause;/* the FROM clause */ Node *whereClause; /* WHERE qualification */ List *groupClause; /* GROUP BY clauses */ Node *havingClause; /* HAVING conditional-Expression */ /* * In a “leaf” node represenTing a VALUES List,the above fIElds are all * null,and instead this fIEld is set.Note that the elements of the * subLists are just Expressions,without ResTarget decoration. Also note * that a List element can be DEFAulT (represented as a SetToDefault * nodE),regardless of the context of the VALUES List. It’s up to parse * analysis to reject that where not valID. */ List *valuesLists; /* untransformed List of Expression Lists */ /* * these fIElds are used in both “leaf” SELEctStmts and upper-level * SELEctStmts. */ List *sortClause;/* sort clause (a List of SortBy’s) */ Node *limitOffset; /* # of result tuples to skip */ Node *limitCount;/* # of result tuples to return */ List *lockingClause; /* FOR updatE (List of LockingClause’s) */ /* * these fIElds are used only in upper-level SELEctStmts. */ Setoperation op; /* type of set op */ boolall; /* ALL specifIEd? */ struct SELEctStmt *larg; /* left child */ struct SELEctStmt *rarg; /* right child */ /* Eventually add fIElds for CORRESPONDING spec here */ } SELEctStmt; delete会解析到： typedef struct deleteStmt { NodeTagtype; RangeVar *relation;/* relation to delete from */ List *usingClause; /* optional using clause for more tables */ Node *whereClause; /* qualifications */ List *returningList; /* List of Expressions to return */ } deleteStmt; update会解析到: typedef struct updateStmt { NodeTagtype; RangeVar *relation;/* relation to update */ List *targetList;/* the target List (of ResTarget) */ Node *whereClause; /* qualifications */ List *fromClause;/* optional from clause for more tables */ List *returningList; /* List of Expressions to return */ } updateStmt; 从定义上看，SELEct比较复杂。其实在PG内部，把SELEct/delete/update当成一样处理，只是最后 找到相应的结果集时采取不同的操作。 POSTGRes.c的804行可以看到这一步操作： parsetree_List = pg_parse_query(query_String); 第一步完成后，只是做了很简单、很粗糙的事情，然后，要进一步进行rewrite,在交给优化器进行优化和 路径选择之前，所有的执行语句都要转换成struct query: typedef struct query { NodeTagtype; CmdTypecommandType; /* SELEct|insert|update|delete|utility */ /* 注意： 如果commandType为: utility，优化器不会对该sql进行进一步优化，因为这个sql 就是一些建表或者其他命令操作，无法进行路径选择和优化，这时候，executor直接 执行utilityStmt这个Node对应的Struct. 对于SELEct|insert|update|delete这些sql，优化器都需要进行评估和优化。 */ querysource querysource; /* where dID I come from? */ BoolCanSetTag;/* do I set the command result tag? */ Node *utilityStmt; /* non-null if this is a non-optimizable * statement */ int resultRelation; /* rtable index of target relation for * INSERT/updatE/deletE; 0 for SELECT */ RangeVar *into; /* target relation for SELECT INTO */ List *intoOptions; /* options from WITH clause */ OnCommitaction intoOnCommit; /* @R_262_10112@ do we do at COMMIT? */ char *in@R_531_10586@bleSpacename;/* table space to use,or NulL */ boolhasAggs;/* has aggregates in tList or havingQual */ boolhasSublinks; /* has subquery Sublink */ List *rtable; /* List of range table entrIEs */ FromExpr *jointree;/* table join tree (FROM and WHERE clauses) */ List *targetList;/* target List (of TargetEntry) */ List *returningList; /* return-values List (of TargetEntry) */ List *groupClause; /* a List of GroupClause’s */ Node *havingQual;/* qualifications applIEd to groups */ List *disTinctClause; /* a List of SortClause’s */ List *sortClause;/* a List of SortClause’s */ Node *limitOffset; /* # of result tuples to skip (int8 expr) */ Node *limitCount;/* # of result tuples to return (int8 expr) */ List *rowMarks;/* a List of RowMarkClause’s */ Node *setoperations; /* set-operation tree if this is top level of * a UNION/INTERSECT/EXCEPT query */ /* * If the resultRelation turns out to be the parent of an inheritance * tree,the plAnner will add all the child tables to the rtable and store * a List of the rTindexes of all the result relations here. This is done * at plan time,not parse time,since we don’t want to commit to the * exact set of child tables at parse time.XXX This fIEld ought to go in * some sort of topPlan plan node,not in the query. */ List *resultRelations; /* Integer List of RT indexes,or NIL */ /* * If the query has a returningList then the plAnner will store a List of * processed targetLists (one per result relation) here.We must have a * separate RETURNING targetList for each result rel because column * numbers may vary within an inheritance tree.In the targetLists,Vars * referencing the result relation will have their original varno and * varattno,while Vars referencing other rels will be converted to have * varno OUTER and varattno referencing a resjunk entry in the top plan * node’s targetList.XXX This fIEld ought to go in some sort of topPlan * plan node,not in the query. */ List *returningLists; /* List of Lists of TargetEntry,or NIL */ } query; 这些rewrite比较复杂，是由一系列的transform函数完成的，具体可以查看analyze.c. 下面把一些sql命令转化后的struct做一个简单的分析。 首先分析utilityStmt,这些命令都比较简单。 (1) create table /* ———————- *create table Statement * * NOTE: in the raw gram.y output,columnDef,ConsTraint,and FkConsTraint * nodes arE intermixed in tableElts,and consTraints is NIl.After parse * analysis,tableElts contains just columnDefs,and consTraints contains * just Constraint nodes (in fact,only CONSTR_checK nodes,in the present * implementation). * ———————- */ typedef struct CreateStmt { // type应该为 T_CreateStmt NodeTagtype; // relation->relname 就是要创建的table名字 RangeVar *relation;/* relation to create */ List *tableElts;/* column deFinitions (List of columnDef) */ // 由于PG的表是可以继承的，这部分先不分析 List *inhRelations; /* relations to inherit from (List of * inhRelation) */ // 这些都是consTraints的定义 List *consTraints; /* consTraints (List of Constraint nodes) */ List *options;/* options from WITH clause */ OnCommitaction oncommit; /* @R_262_10112@ do we do at COMMIT? */ char *tablespacename; /* table space to use,or NulL */ } CreateStmt; 其中最重要的就是：tableElts这个字段，里面包含了要创建table的所有columns. 我写了几行代码，可以遍历这一List. List *scheR_704_11845@a; ListCell *col; elog(LOG,“begin create:%s”,((CreateStmt *)parsetreE)->relation->relname); scheR_704_11845@a = ((CreateStmt *)parsetreE)->tableElts; // 遍历 foreach(col,scheR_704_11845@a) { columnDef*entry = lfirst(col); elog(LOG,“column name:%s column type:%s”,entry->colname,TypenameToString(entry->typeName)); } 建表语句： pgsql=# create table lijianghua ( name varchar(100),pass varchar(100)); create table log输出： LOG:begin create:lijianghua LOG:column name:name column type:pg_catalog.varchar LOG:column name:pass column type:pg_catalog.varchar (2) drop object 删除一个对象时，比如：drop table/drop vIEw……,命令会被解析到DropStmt struct: /* ———————- *drop table|Sequence|VIEw|Index|Type|Domain|Conversion|scheR_704_11845@a Statement * ———————- */ typedef struct DropStmt { NodeTagtype; // 需要删除的对象列表 List *objects;/* List of subLists of names (as Values) */ // 对象类型 ObjectType removeType;/* object type */ DropBehavior behavior;/* REStriCT or CASCADE behavior */ boolmissing_ok;/* skip error if object is missing? */ } DropStmt; ObjectType的定义也非常简单： typedef enum ObjectType { OBjeCT_AGGREGATE,OBjeCT_CAST,OBjeCT_columN,OBjeCT_CONSTraiNT,OBjeCT_CONVERSION,OBjeCT_DATABASE,OBjeCT_DOMAIN,OBjeCT_FUNCTION,OBjeCT_INDEX,OBjeCT_LANGUAGE,OBjeCT_LARGEOBjeCT,OBjeCT_OPCLASS,OBjeCT_OPERATOR,OBjeCT_RolE,OBjeCT_RulE,OBjeCT_scheR_704_11845@A,OBjeCT_SEQUENCE,OBjeCT_table,OBjeCT_tableSPACE,OBjeCT_trigGER,object_type,OBjeCT_VIEW } ObjectType; 同样，我也写了几行代码，进行了相关验证： if(parsetree->type == T_DropStmt) { List *tables; ListCell *table; tables = ((DropStmt *)parsetreE)->objects; foreach(table,tables) { List *names = (List *) lfirst(tablE); RangeVar *rel; if(((DropStmt *)parsetreE)->removeType == OBjeCT_tablE) { rel = makeRangeVarFromnameList(names); elog(LOG,“want to DELETE TABLE:%s”,rel->relname); } } } sql语句： pgsql=# drop table test,test21; drop table log输出： LOG:want to DELETE TABLE:test LOG:want to DELETE TABLE:test21 (3) 把比较复杂的Insert/update/delete/SELEct做一些详细的分析

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