转载：PostgreSQL服务过程中的那些事二：Pg服务进程处理简单查询
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转载来自： PostgreSQL服务过程中的那些事二：Pg服务进程处理简单查询六：执行器执行 blog.csdn.net/beiigang beigang.iteye.com
话说查询“select cname,comp from test1,test2 where test1.id=test2.id;”发送到服务器端，走查询分支exec_simple_query，先调用start_xact_command初始化了事务管理相关对象和资源，接着调用pg_parse_query，通过Lex和Yacc对传入SQL语句进行词法语法解析，生成解析树。下来调用GetTransactionSnapshot方法做内存快照，然后调用pg_analyze_and_rewrite方法，进行语义分析把parsetree转换成querytree，然后对该querytree进行重写。接着调用pg_plan_queries方法，根据querytree做查询规划，生成查询计划树plantree。然后调用了一系列方法CreatePortal、PortalStart、PortalSetResultFormat、CreateDestReceiver、PortalRun、PortalDrop，创建portal、初始化portal、设置结果列格式、创建目的地接收者、运行portal执行查询并返回结果，然后释放portal相关资源，再调用finish_xact_command释放事务相关资源。这个例子终于执行完了。 1 下面是执行plantree的调用序列图。
执行plantree的调用序列图 上图红色方框中显示了执行plantree的过程，主要分为portal创建和初始化（CreatePortal、PortalStart）、执行（PortalRun）、释放资源（PortalDrop）三个部分。portal是个抽象概念，它表示一个正在运行或可运行query的执行状态。Portal支持SQL层的CURSOR和协议层的portal。从上图中可以看出，在各个部分，portal调用了执行器executor的对应方法ExecutorStart、ExecutorRun、ExecutorDrop完成了相关操作。 简单描述一下执行过程，方法CreatePortal在内存上下文PortalMemory里创建portal，并在portal管理器"Portal hash"中注册（参见《PostgreSQL服务过程中的那些事一：启动postgres服务进程一.七：初始化portal管理环境》）；调用PortalDefineQuery为新建的portal设置sourceText（就是例子里的源SQL语句）、stmts（就是上一节讨论的plantree列表）等字段，将portal状态设置为PORTAL_DEFINED；再调用PortalStart初始化portal，在该例子里选择PORTAL_ONE_SELECT策略，调用CreateQueryDesc方法，为portal创建查询描述符，将portal状态设置为PORTAL_READY；调用方法PortalRun，根据选择策略调用相应方法，根据portal相关由plantree转化来的各节点结构由下至上逐层进行处理，涉及扫描数据、进行投射、结果缓存等；最后调用PortalDrop释放portal相关资源。 portal有多个执行策略，依赖于执行什么样的query（其实就是根据不同的SQL语句调用不同的方法以完成相应操作）。（注意：在所有情况下，一个portal仅执行一个源SQL query，并且从用户的视点，仅产生一个结果。但是，规则重写器可以扩展一个源query成0或多个实际的query。）下面是portal的四种策略 PORTAL_ONE_SELECT：这个portal包含一个SELECT查询。我们增加运行一个执行器作为被要求的结果。这个策略还支持可持有的cursor（为了事务结束后访问结果，执行器结果可以被转储到一个tuplestore里）。 PORTAL_ONE_RETURNING：这个portal包含一个伴有RETURNING子句的INSERT/UPDATE/DELETE查询（由规则重写器重写增加的可能的辅助查询/query）。在第一次执行时，我们运行portal以完成和转储主query的结果到portal的tuplestore里；然后这个结果按要求返回给用户。（我们不支持query的部分遍历悬挂，因为AFTER触发器代码不能处理，并且还因为我们不想在执行所有辅助query时冒失败风险。） PORTAL_ONE_MOD_WITH：portal包含一个SELECT qiery，但它包含数据修改CTE。这个目前和处理PORTAL_ONE_RETURNING的情况一样，因为需要触发触发器的可能性。将来处理这种情况的行为可以更像PORTAL_ONE_SELECT。 PORTAL_UTIL_SELECT：portal包含一个utility语句，其返回一个象SELECT那样的结果（例如，WXPLAIN或者SHOW）。在第一次执行时，我们运行这个语句任何转储其结果到portal的tuplestore里；然后这个结果按要求的返回给客户端。 PORTAL_MULTI_QUERY：所有其它情况。这儿，我们不支持portal执行：portal的query会被运行以完成第一次调用。 下面是portal和其执行状态、策略的类型定义及执行器状态结构定义，其他涉及到节点结构定义略去。 typedefenumPortalStrategy { PORTAL_ONE_SELECT, PORTAL_ONE_RETURNING, PORTAL_ONE_MOD_WITH, PORTAL_UTIL_SELECT, PORTAL_MULTI_QUERY }PortalStrategy; typedefenumPortalStatus { PORTAL_NEW,/* freshly created */ PORTAL_DEFINED,/* PortalDefineQuery done */ PORTAL_READY,/* PortalStart complete,can run it */ PORTAL_ACTIVE,/* portal is running (can't delete it) */ PORTAL_DONE,/* portal is finished (don't re-run it) */ PORTAL_FAILED/* portal got error (can't re-run it) */ }PortalStatus; typedefstructPortalData *Portal; typedefstructPortalData { /* Bookkeeping data */ constchar*name;/* portal's name */ prepStmtName;/* source prepared statement (NULL if none) */ MemoryContextheap;/* subsidiary memory for portal */ ResourceOwnerresowner;/* resources owned by portal */ void(*cleanup) (Portalportal);/* cleanup hook */ SubTransactionIdcreateSubid;/* the ID of the creatingsubxact*/ /* * if createSubid is InvalidSubTransactionId,the portal is held over from * a previous transaction */ /* The query or queries the portal will execute */ sourceText;/* text of query (as of 8.4,never NULL) */ commandTag;/* command tag for original query */ List*stmts;/* PlannedStmts and/or utility statements */ CachedPlan*cplan;/* CachedPlan,ifstmtsare from one */ ParamListInfoportalParams;/*paramsto pass to query */ /* Features/options */ PortalStrategystrategy;/* see above */ intcursorOptions;/* DECLARE CURSOR option bits */ /* Status data */ PortalStatusstatus;/* see above */ boolportalPinned;/* a pinned portal can't be dropped */ /* If not NULL,Executor is active; call ExecutorEnd eventually: */ QueryDesc*queryDesc;/* info needed for executor invocation */ /* If portal returns tuples,this is theirtupdesc: */ TupleDesctupDesc;/* descriptor for result tuples */ /* and these are the format codes to use for the columns: */ int16*formats;/* a format code for each column */ * Where we store tuples for a held cursor or a PORTAL_ONE_RETURNING or * PORTAL_UTIL_SELECT query.(A cursor held past the end of its * transaction no longer has any active executor state.) */ Tuplestorestate*holdStore;/* store forholdablecursors */ holdContext;/* memory containing holdStore */ * atStart,atEnd and portalPos indicate the current cursor position. * portalPos is zero before the first row,N after fetching N'th row of * query.After we run off the end,portalPos = # of rows in query,and * atEnd is true.If portalPos overflows,set posOverflow (this causes us * to stop relying on its value for navigation).Note that atStart * implies portalPos == 0,but not the reverse (portalPos could have * overflowed). atStart; atEnd; posOverflow; longportalPos; /* Presentation data,primarily used by the pg_cursors system view */ TimestampTzcreation_time;/* time at which this portal was defined */ visible;/* include this portal in pg_cursors? */ }PortalData; 执行器调用的主工作状态 typedefstructEState { NodeTagtype; /* Basic state for all query types: */ ScanDirectiones_direction;/* current scan direction */ Snapshotes_snapshot;/* timequalto use */ es_crosscheck_snapshot;/*crosschecktimequalfor RI */ es_range_table;/* List of RangeTblEntry */ PlannedStmt*es_plannedstmt;/* link to top of plan tree */ JunkFilter*es_junkFilter;/* top-level junk filter,if any */ /* If query can insert/delete tuples,the command ID to mark them with */ CommandIdes_output_cid; /* Info about target table(s) for insert/update/delete queries: */ ResultRelInfo*es_result_relations;/* array of ResultRelInfos */ es_num_result_relations;/* length of array */ es_result_relation_info;/* currently active arrayelt*/ /* Stuff used for firing triggers: */ es_trig_target_relations;/* trigger-only ResultRelInfos */ TupleTableSlot*es_trig_tuple_slot;/* for trigger output tuples */ es_trig_oldtup_slot;/* for TriggerEnabled */ /* Parameter info: */ es_param_list_info;/* values of externalparams*/ ParamExecData*es_param_exec_vals;/* values of internalparams*/ /* Other working state: */ es_query_cxt;/* per-query context in which EState lives */ es_tupleTable;/* List of TupleTableSlots */ es_rowMarks;/* List of ExecRowMarks */ uint32es_processed;/* # of tuples processed */ Oides_lastoid;/* lastoidprocessed (by INSERT) */ es_top_eflags;/*eflagspassed to ExecutorStart */ es_instrument;/* OR of InstrumentOption flags */ es_select_into;/* true if doing SELECT INTO */ es_into_oids;/* true to generate OIDs in SELECT INTO */ es_finished;/* true when ExecutorFinish is done */ es_exprcontexts;/* List of ExprContexts within EState */ es_subplanstates;/* List of PlanState for SubPlans */ es_auxmodifytables;/* List of secondary ModifyTableStates */ * this ExprContext is for per-output-tuple operations,such as constraint * checks and index-value computations.It will be reset for each output * tuple.Note that it will be created only if needed. ExprContext*es_per_tuple_exprcontext; * These fields are for re-evaluating planqualswhen an updated tuple is * substituted in READ COMMITTED mode.es_epqTuple[] contains tuples that * scan plan nodes should return instead of whatever they'd normally * return,or NULL if nothing to return; es_epqTupleSet[] is true if a * particular array entry is valid; and es_epqScanDone[] is state to * remember if the tuple has been returned already.Arrays are of size * list_length(es_range_table) and are indexed by scan nodescanrelid- 1. HeapTuple*es_epqTuple;/* array of EPQ substitute tuples */ bool*es_epqTupleSet;/* true if EPQ tuple is provided */ es_epqScanDone;/* true if EPQ tuple has been fetched */ * this field added at end ofstructto avoid post-release ABI breakage in * existing release branches.It'll be in a more logical place in 9.2. es_trig_newtup_slot;/* for TriggerEnabled */ }EState; 下面是执行这个查询的portal相关内存结构图：
portal相关内存结构图 就到这儿吧。 （编辑：李大同） 【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容! |