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这篇文章主要介绍“PostgreSQL中Review exec_simple_query函数的实现逻辑是什么”,在日常操作中,相信很多人在PostgreSQL中Review exec_simple_query函数的实现逻辑是什么问题上存在疑惑,小编查阅了各式资料,整理出简单好用的操作方法,希望对大家解答”PostgreSQL中Review exec_simple_query函数的实现逻辑是什么”的疑惑有所帮助!接下来,请跟着小编一起来学习吧!
exec_simple_query函数由PostgresMain函数调用,其调用栈如下:
#3 0x00000000008c5c35 in exec_simple_query (query_string=0x2eed1a8 "select * from t1;") at postgres.c:1050 #4 0x00000000008ca0f8 in PostgresMain (argc=1, argv=0x2f16cb8, dbname=0x2f16b20 "testdb", username=0x2ee9d48 "xdb") at postgres.c:4159 #5 0x0000000000825880 in BackendRun (port=0x2f0eb00) at postmaster.c:4361 #6 0x0000000000824fe4 in BackendStartup (port=0x2f0eb00) at postmaster.c:4033 #7 0x0000000000821371 in ServerLoop () at postmaster.c:1706 #8 0x0000000000820c09 in PostmasterMain (argc=1, argv=0x2ee7d00) at postmaster.c:1379 #9 0x0000000000747ea7 in main (argc=1, argv=0x2ee7d00) at main.c:228
该函数的实现逻辑详见代码注释.
/* * exec_simple_query * * Execute a "simple Query" protocol message. * 响应并执行"simple Query"协议消息请求 */ /* 输入: query_string-SQL语句 输出: 无 */ static void exec_simple_query(const char *query_string) { CommandDest dest = whereToSendOutput;//输出到哪里的定义 MemoryContext oldcontext;//存储原内存上下文 List *parsetree_list;//分析树列表 ListCell *parsetree_item;//分析树中的ITEM bool save_log_statement_stats = log_statement_stats;//是否保存统计信息,false bool was_logged = false;//Log? bool use_implicit_block;//是否使用隐式事务块 char msec_str[32]; /* * Report query to various monitoring facilities. * 监控信息 */ debug_query_string = query_string; pgstat_report_activity(STATE_RUNNING, query_string);//统计信息 TRACE_POSTGRESQL_QUERY_START(query_string); /* * We use save_log_statement_stats so ShowUsage doesn't report incorrect * results because ResetUsage wasn't called. * 如save_log_statement_stats为T,则调用ResetUsage函数 */ if (save_log_statement_stats) ResetUsage(); /* * Start up a transaction command. All queries generated by the * query_string will be in this same command block, *unless* we find a * BEGIN/COMMIT/ABORT statement; we have to force a new xact command after * one of those, else bad things will happen in xact.c. (Note that this * will normally change current memory context.) * 启动一个事务命令。 * 由query_string生成的所有查询都将位于同一个命令块中,*除非*找到BEGIN/COMMIT/ABORT语句; * 必须在其中一个命令之后强制执行新的xact命令,否则xact.c中会发生意想不到事情。 * (注意,这通常会改变当前内存上下文。) */ start_xact_command();//启动事务 /* * Zap any pre-existing unnamed statement. (While not strictly necessary, * it seems best to define simple-Query mode as if it used the unnamed * statement and portal; this ensures we recover any storage used by prior * unnamed operations.) * 删除任何预先存在的未命名语句。 * (虽然不是严格必要的,但最好定义简单查询模式,就像使用未命名语句和门户接口一样; * 这确保我们恢复以前未命名操作所使用的存储信息。) */ drop_unnamed_stmt();//清除未命名语句 /* * Switch to appropriate context for constructing parsetrees. * 切换至合适的内存上下文 */ oldcontext = MemoryContextSwitchTo(MessageContext);//切换内存上下文 /* * Do basic parsing of the query or queries (this should be safe even if * we are in aborted transaction state!) * 执行查询(或多个查询)的基本解析 * (即使我们处于中止的事务状态,这也应该是安全的!) */ parsetree_list = pg_parse_query(query_string);//解析输入的查询语句,获得解析树List(元素是RawStmt nodes) /* Log immediately if dictated by log_statement */ //如需要记录日志,则Log这些信息 if (check_log_statement(parsetree_list))//日志记录 { ereport(LOG, (errmsg("statement: %s", query_string), errhidestmt(true), errdetail_execute(parsetree_list))); was_logged = true; } /* * Switch back to transaction context to enter the loop. * 切换回去原事务上下文 */ MemoryContextSwitchTo(oldcontext);//切换回原内存上下文 /* * For historical reasons, if multiple SQL statements are given in a * single "simple Query" message, we execute them as a single transaction, * unless explicit transaction control commands are included to make * portions of the list be separate transactions. To represent this * behavior properly in the transaction machinery, we use an "implicit" * transaction block. * 由于历史原因,如果在单个“简单查询”消息中给出了多个SQL语句,那么我们将作为单个事务执行它们, * 除非包含显式事务控制命令,使链表中的部分成为单独的事务。 * 为了在事务机制中正确地表示这种行为,使用了一个“隐式”事务块。 */ //如果分析树条目>1,使用隐式事务块(多条SQL语句在同一个事务中) use_implicit_block = (list_length(parsetree_list) > 1); /* * Run through the raw parsetree(s) and process each one. * 对分析树中的每一个条目进行处理 */ foreach(parsetree_item, parsetree_list)// { RawStmt *parsetree = lfirst_node(RawStmt, parsetree_item);//分析树List中的元素为RawStmt指针类型 bool snapshot_set = false;//是否设置快照? const char *commandTag;//命令标识 char completionTag[COMPLETION_TAG_BUFSIZE];//完成标记,如INSERT 0 1之类的字符串 List *querytree_list,//查询树List *plantree_list;//执行计划List Portal portal;//“门户”变量 DestReceiver *receiver;//目标接收端 int16 format;// /* * Get the command name for use in status display (it also becomes the * default completion tag, down inside PortalRun). Set ps_status and * do any special start-of-SQL-command processing needed by the * destination. * 获取用于状态显示的命令名称(在PortalRun内部,它也成为默认的完成标记)。 * 设置ps_status并执行目标语句所需要的start-of-SQL-command处理。 */ commandTag = CreateCommandTag(parsetree->stmt);//创建命令标记,插入数据则为INSERT set_ps_display(commandTag, false); BeginCommand(commandTag, dest);//do Nothing! /* * If we are in an aborted transaction, reject all commands except * COMMIT/ABORT. It is important that this test occur before we try * to do parse analysis, rewrite, or planning, since all those phases * try to do database accesses, which may fail in abort state. (It * might be safe to allow some additional utility commands in this * state, but not many...) * 如果我们处于事务中止状态中,拒绝除COMMIT/ABORT之外的所有命令。 * 在尝试进行解析分析、重写或计划之前进行此测试是很重要的, * 因为所有这些阶段都尝试进行数据库访问,而在abort状态下可能会失败。 * (在这种状态下允许一些额外的实用程序命令可能是安全的,但不是很多……) */ if (IsAbortedTransactionBlockState() && !IsTransactionExitStmt(parsetree->stmt)) ereport(ERROR, (errcode(ERRCODE_IN_FAILED_SQL_TRANSACTION), errmsg("current transaction is aborted, " "commands ignored until end of transaction block"), errdetail_abort())); /* Make sure we are in a transaction command */ start_xact_command();//确认在事务中 /* * If using an implicit transaction block, and we're not already in a * transaction block, start an implicit block to force this statement * to be grouped together with any following ones. (We must do this * each time through the loop; otherwise, a COMMIT/ROLLBACK in the * list would cause later statements to not be grouped.) * 如果使用隐式事务块(还没有使用atransaction块),启动一个隐式事务块来强制将该语句与以下语句组合在一起。 * (我们每次通过循环时都必须这样做;否则,链表中的提交/回滚将导致后面的语句没有分组。 */ if (use_implicit_block) BeginImplicitTransactionBlock();//隐式事务,进入事务块 /* If we got a cancel signal in parsing or prior command, quit */ //如果在解析或者解析之前接收到取消的信号,则退出 CHECK_FOR_INTERRUPTS(); /* * Set up a snapshot if parse analysis/planning will need one. * 如果解析/分析/计划过程需要snapshot,则创建一个 */ if (analyze_requires_snapshot(parsetree))//是否需要快照进行分析?增删改查均需要 { PushActiveSnapshot(GetTransactionSnapshot());//活动快照入栈 snapshot_set = true; } /* * OK to analyze, rewrite, and plan this query. * 准备工作妥当,可以进行分析/重写和计划查询语句了 * * Switch to appropriate context for constructing querytrees (again, * these must outlive the execution context). * 切换至合适的内存上下文中 */ oldcontext = MemoryContextSwitchTo(MessageContext);//切换内存上下文 //根据分析树获得查询树,返回List(元素为Query) querytree_list = pg_analyze_and_rewrite(parsetree, query_string, NULL, 0, NULL); //根据查询树获取计划树,返回List(元素为PlannedStmt) plantree_list = pg_plan_queries(querytree_list, CURSOR_OPT_PARALLEL_OK, NULL); /* Done with the snapshot used for parsing/planning */ //启用了快照,则出栈 if (snapshot_set) PopActiveSnapshot();// /* If we got a cancel signal in analysis or planning, quit */ //如接收到取消信号,则退出 CHECK_FOR_INTERRUPTS(); /* * Create unnamed portal to run the query or queries in. If there * already is one, silently drop it. * 创建匿名的门户接口来执行查询,如Portal已存在,则先drop it */ portal = CreatePortal("", true, true);//创建匿名Portal变量 /* Don't display the portal in pg_cursors */ //该portal不在pg_cursors中出现 portal->visible = false; /* * We don't have to copy anything into the portal, because everything * we are passing here is in MessageContext, which will outlive the * portal anyway. * 不需要将任何内容复制到Portal中, * 因为在这里传递的所有内容都在MessageContext中,它的生命周期将比Portal更长。 */ PortalDefineQuery(portal, NULL, query_string, commandTag, plantree_list, NULL);//给Portal变量赋值 /* * Start the portal. No parameters here. * 启动Portal,不需要参数 */ PortalStart(portal, NULL, 0, InvalidSnapshot);//为PortalRun作准备 /* * Select the appropriate output format: text unless we are doing a * FETCH from a binary cursor. (Pretty grotty to have to do this here * --- but it avoids grottiness in other places. Ah, the joys of * backward compatibility...) * 选择适当的输出格式:文本,除了我们正在从二进制游标进行提取。 * (不得不在这里这样做实在是太糟糕了——但在其他地方却避免了这种情况。啊,向后兼容的乐趣…… */ format = 0; /* 默认为TEXT;TEXT is default */ if (IsA(parsetree->stmt, FetchStmt)) { FetchStmt *stmt = (FetchStmt *) parsetree->stmt; if (!stmt->ismove) { Portal fportal = GetPortalByName(stmt->portalname); if (PortalIsValid(fportal) && (fportal->cursorOptions & CURSOR_OPT_BINARY)) format = 1; /* 二进制格式;BINARY */ } } PortalSetResultFormat(portal, 1, &format);//设置结果返回的格式,默认为TEXT /* * Now we can create the destination receiver object. * 现在可以创建目标接收器对象了 */ //创建目标接收器(如使用psql则为:printtup DestReceiver) receiver = CreateDestReceiver(dest); if (dest == DestRemote) SetRemoteDestReceiverParams(receiver, portal); /* * Switch back to transaction context for execution. * 切换回原内存上下文 */ MemoryContextSwitchTo(oldcontext);// /* * Run the portal to completion, and then drop it (and the receiver). * 执行PortalRun,然后清除 */ (void) PortalRun(portal, FETCH_ALL, true, /* always top level */ true, receiver, receiver, completionTag);//执行 //执行完毕,销毁接收器 receiver->rDestroy(receiver); //清除Portal中的资源 PortalDrop(portal, false); if (lnext(parsetree_item) == NULL)//所有语句已执行完毕 { /* * If this is the last parsetree of the query string, close down * transaction statement before reporting command-complete. This * is so that any end-of-transaction errors are reported before * the command-complete message is issued, to avoid confusing * clients who will expect either a command-complete message or an * error, not one and then the other. Also, if we're using an * implicit transaction block, we must close that out first. * 如果这是查询字符串的最后一个parsetree,在报告命令完成之前关闭事务语句。 * 这样,在发出命令完整的消息之前就会报告任何事务结束错误,以避免混淆视听, * 因为客户端希望看到命令完整的消息或错误,而不是一个错误,然后是另一个错误。 * 另外,如果我们使用隐式事务块,我们必须首先关闭它。 */ if (use_implicit_block) EndImplicitTransactionBlock();//结束事务 finish_xact_command();//结束事务 } else if (IsA(parsetree->stmt, TransactionStmt))//事务语句?BEGIN/COMMIT/ABORT... { /* * If this was a transaction control statement, commit it. We will * start a new xact command for the next command. * 如果这是一个事务控制语句,提交此语句。 * 我们将为下一个命令启动一个新的xact命令。 */ finish_xact_command(); } else { /* * We need a CommandCounterIncrement after every query, except * those that start or end a transaction block. * 在每次查询之后,我们都需要一个CommandCounterIncrement,除了那些启动或结束事务块的查询。 */ CommandCounterIncrement();//命令+1(对应Tuple中的cid) } /* * Tell client that we're done with this query. Note we emit exactly * one EndCommand report for each raw parsetree, thus one for each SQL * command the client sent, regardless of rewriting. (But a command * aborted by error will not send an EndCommand report at all.) * 告诉客户端已经完成了这个查询。注意,对于每个原始的parsetree,只发出一个EndCommand报告, * 因此,对于客户机发送的每个SQL命令,只发出一个EndCommand报告,而不考虑重写。 * (注:由于错误而中止的命令根本不会发送EndCommand报告。) */ EndCommand(completionTag, dest);//命令Done } /* end loop over parsetrees */ //所有语句结束 /* * Close down transaction statement, if one is open. (This will only do * something if the parsetree list was empty; otherwise the last loop * iteration already did it.) * 如果事务是打开的,则关闭。 * (只有当parsetree链表为空时,才会执行某些操作;否则,最后一次循环迭代已经完成了。 */ finish_xact_command(); /* * If there were no parsetrees, return EmptyQueryResponse message. * 如果parsetrees链表已清空,返回EmptyQueryResponse消息 */ if (!parsetree_list) NullCommand(dest); /* * Emit duration logging if appropriate. * 如需要记录日志,则在合适的时候记录 */ switch (check_log_duration(msec_str, was_logged)) { case 1: ereport(LOG, (errmsg("duration: %s ms", msec_str), errhidestmt(true))); break; case 2: ereport(LOG, (errmsg("duration: %s ms statement: %s", msec_str, query_string), errhidestmt(true), errdetail_execute(parsetree_list))); break; } if (save_log_statement_stats) ShowUsage("QUERY STATISTICS"); TRACE_POSTGRESQL_QUERY_DONE(query_string); debug_query_string = NULL; }
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