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代做网站多少钱,什么兼职网站可以做视频剪辑,微信网页注册入口,用织梦做领券网站目录结构 注#xff1a;提前言明 本文借鉴了以下博主、书籍或网站的内容#xff0c;其列表如下#xff1a; 1、参考书籍#xff1a;《PostgreSQL数据库内核分析》 2、参考书籍#xff1a;《数据库事务处理的艺术#xff1a;事务管理与并发控制》 3、PostgreSQL数据库仓库… 目录结构 注提前言明 本文借鉴了以下博主、书籍或网站的内容其列表如下 1、参考书籍《PostgreSQL数据库内核分析》 2、参考书籍《数据库事务处理的艺术事务管理与并发控制》 3、PostgreSQL数据库仓库链接点击前往 4、日本著名PostgreSQL数据库专家 铃木启修 网站主页点击前往 5、参考书籍《PostgreSQL中文手册》 6、参考书籍《PostgreSQL指南内幕探索》点击前往 7、深度解析 PostgreSQL Protocol v3.0一点击前往 8、技术贴 | 深度解析 PostgreSQL Protocol v3.0二— 扩展查询点击前往 1、本文内容全部来源于开源社区 GitHub和以上博主的贡献本文也免费开源可能会存在问题评论区等待大佬们的指正 2、本文目的开源共享 抛砖引玉 一起学习 3、本文不提供任何资源 不存在任何交易 与任何组织和机构无关 4、大家可以根据需要自行 复制粘贴以及作为其他个人用途但是不允许转载 不允许商用 写作不易还请见谅 5、本文内容基于PostgreSQL master源码开发而成 深入理解PostgreSQL数据库之Protocol message构造和解析逻辑 文章快速说明索引功能使用背景说明功能实现源码解析辅助调试信息前端信息构造后端消息解析 文章快速说明索引 学习目标 做数据库内核开发久了就会有一种 少年得志年少轻狂 的错觉然鹅细细一品觉得自己其实不算特别优秀 远远没有达到自己想要的。也许光鲜的表面掩盖了空洞的内在每每想到于此皆有夜半临渊如履薄冰之感。为了睡上几个踏实觉即日起 暂缓其他基于PostgreSQL数据库的兼容功能开发近段时间 将着重于学习分享Postgres的基础知识和实践内幕。 学习内容详见目录 1、深入理解PostgreSQL数据库之Protocol message构造和解析逻辑 学习时间 2024年04月17日 22:14:16 星期三 学习产出 1、PostgreSQL数据库基础知识回顾 1个 2、CSDN 技术博客 1篇 3、PostgreSQL数据库内核深入学习 注下面我们所有的学习环境是Centos8PostgreSQL masterOracle19CMySQL8.0 postgres# select version();version
————————————————————————————————————PostgreSQL 17devel on x86_64-pc-linux-gnu, compiled by gcc (GCC) 8.5.0 20210514 (Red Hat 8.5.0-21), 64-bit (1 row)postgres##—————————————————————————–#SQL select * from v$version; BANNER Oracle Database 19c EE Extreme Perf Release 19.0.0.0.0 - Production BANNER_FULL Oracle Database 19c EE Extreme Perf Release 19.0.0.0.0 - Production Version 19.17.0.0.0 BANNER_LEGACY Oracle Database 19c EE Extreme Perf Release 19.0.0.0.0 - Production

CON_ID 0#—————————————————————————–#mysql select version();

1 row in set (0.06 sec)mysql功能使用背景说明 在之前的博客 PostgreSQL的学习心得和知识总结一百三十七|深入理解PostgreSQL数据库之Add support for Close on portals and statements点击前往 的结尾的时候简单介绍了一下close的message构造 这里解释一下close消息的构造如下 /* construct the Close message */if (pqPutMsgStart(command, conn) 0 ||pqPutc(type, conn) 0 || // 1字节 SpqPuts(target, conn) 0 || // strlen(p2) 1 3pqPutMsgEnd(conn) 0) // (conn-outMsgEnd - conn-outMsgStart)长度 4字节goto sendFailed;功能实现源码解析 辅助调试信息 上面是通过抓包工具得到的接下来我们看一下PostgreSQL中提供的debug方式如下 #include iostream#include libpq-fe.husing namespace std;int main() {const char *conninfo hostlocalhost port5432 userpostgres dbnamepostgres password1;const char *dropTableCmd drop table if exists t1;;const char *createTableCmd create table t1(id int, name text);;const char *insertCmd insert into t1 values(1, Oracle), (2, MySQL), (3, SQL Server);;const char *prepareCmd0 table t1;;const char *prepareCmd1 select * from t1 where id \(1;;const char *prepareCmd2 select * from t1 where id \)1 and name \(2;;PGresult *result NULL;ExecStatusType result_status;int n_rows 0, ntups 0;const char *values2[2] {2, MySQL};FILE *file fopen(/home/postgres/test/bin/1.txt, w);PGconn *conn PQconnectdb(conninfo);PQtrace(conn, file);if (PQstatus(conn) CONNECTION_OK){cout 连接PostgreSQL数据库 成功 endl;if (PQexec(conn, dropTableCmd) ! NULL){cout 删除表成功 endl;}if (PQexec(conn, createTableCmd) ! NULL){cout 创建表成功 endl;}if (PQexec(conn, insertCmd) ! NULL){cout 插入表成功 endl endl;}/* ---------------------------------------------------------------- */// prepareif (PQsendPrepare(conn, p23456789, prepareCmd2, 2, NULL) ! NULL) // 异步{cout prepare p23456789 send成功 endl;}while (NULL ! (result PQgetResult(conn))){result_status PQresultStatus(result);if ((PGRES_EMPTY_QUERY ! result_status) (PGRES_COMMAND_OK ! result_status) (PGRES_TUPLES_OK ! result_status) (PGRES_NONFATAL_ERROR ! result_status)){cout prepare p23456789 失败 endl;}else{n_rows atoi(PQcmdTuples(result));ntups PQntuples(result);cout prepare p23456789 成功 n_rows: n_rows ntups: ntups endl endl;}PQclear(result);}/* ---------------------------------------------------------------- */// exec_preparedif (PQsendQueryPrepared(conn, p23456789, 2, values2, NULL, NULL, 0) ! NULL) // 异步{cout exec prepare p23456789 send成功 endl;}while (NULL ! (result PQgetResult(conn))){result_status PQresultStatus(result);if ((PGRES_EMPTY_QUERY ! result_status) (PGRES_COMMAND_OK ! result_status) (PGRES_TUPLES_OK ! result_status) (PGRES_NONFATAL_ERROR ! result_status)){cout exec prepare p23456789 失败 endl;}else{n_rows atoi(PQcmdTuples(result));ntups PQntuples(result);cout exec prepare p23456789 send成功 n_rows: n_rows ntups: ntups endl endl;}PQclear(result);}/* ---------------------------------------------------------------- */// deallocateresult PQexec(conn, select pg_sleep(60);); // 同步PQclear(result);if (PQsendClosePrepared(conn, p23456789) ! NULL) // 异步{cout close prepare p23456789 send成功 endl;}while (NULL ! (result PQgetResult(conn))){result_status PQresultStatus(result);if ((PGRES_EMPTY_QUERY ! result_status) (PGRES_COMMAND_OK ! result_status) (PGRES_TUPLES_OK ! result_status) (PGRES_NONFATAL_ERROR ! result_status)){cout close prepare p23456789 失败 endl;}else{n_rows atoi(PQcmdTuples(result));ntups PQntuples(result);cout close prepare p23456789 成功 n_rows: n_rows ntups: ntups endl endl;}PQclear(result);}/* ---------------------------------------------------------------- */PQfinish(conn);PQuntrace(conn);cout 与PostgreSQL数据库连接 关闭 endl;}else{cout 连接失败 endl;}fclose(file);return 0; }/** export LD_LIBRARY_PATH\)LD_LIBRARY_PATH:\(PG_HOME/lib** g libpqtest2.cpp -lpq -L/home/postgres/test/lib -I/home/postgres/test/include -o main -w -g -O0*/执行结果以及打印信息如下 [postgreslocalhost:~/test/bin]\) ./main 连接PostgreSQL数据库 成功 删除表成功 创建表成功 插入表成功prepare p23456789 send成功 prepare p23456789 成功 n_rows: 0 ntups: 0exec prepare p23456789 send成功 exec prepare p23456789 send成功 n_rows: 1 ntups: 1close prepare p23456789 send成功 close prepare p23456789 成功 n_rows: 0 ntups: 0与PostgreSQL数据库连接 关闭 [postgreslocalhost:/test/bin]\( cat 1.txt 2024-04-16 20:22:43.371152 F 29 Query drop table if exists t1; 2024-04-16 20:22:43.381514 B 15 CommandComplete DROP TABLE 2024-04-16 20:22:43.381531 B 5 ReadyForQuery I 2024-04-16 20:22:43.381561 F 40 Query create table t1(id int, name text); 2024-04-16 20:22:43.388197 B 17 CommandComplete CREATE TABLE 2024-04-16 20:22:43.388215 B 5 ReadyForQuery I 2024-04-16 20:22:43.388239 F 73 Query insert into t1 values(1, Oracle), (2, MySQL), (3, SQL Server); 2024-04-16 20:22:43.388729 B 15 CommandComplete INSERT 0 3 2024-04-16 20:22:43.388736 B 5 ReadyForQuery I 2024-04-16 20:22:43.388758 F 62 Parse p23456789 select * from t1 where id \)1 and name $2; 0 2024-04-16 20:22:43.388762 F 4 Sync 2024-04-16 20:22:43.390728 B 4 ParseComplete 2024-04-16 20:22:43.390767 B 5 ReadyForQuery I 2024-04-16 20:22:43.390772 F 37 Bind p23456789 0 2 1 2 5 MySQL 1 0 2024-04-16 20:22:43.390775 F 6 Describe P 2024-04-16 20:22:43.390777 F 9 Execute 0 2024-04-16 20:22:43.390779 F 4 Sync 2024-04-16 20:22:43.392433 B 4 BindComplete 2024-04-16 20:22:43.392483 B 50 RowDescription 2 id 16403 1 23 4 -1 0 name 16403 2 25 65535 -1 0 2024-04-16 20:22:43.392494 B 20 DataRow 2 1 2 5 MySQL 2024-04-16 20:22:43.392500 B 13 CommandComplete SELECT 1 2024-04-16 20:22:43.392644 B 5 ReadyForQuery I 2024-04-16 20:22:43.392725 F 25 Query select pg_sleep(60); 2024-04-16 20:23:43.406609 B 33 RowDescription 1 pg_sleep 0 0 2278 4 -1 0 2024-04-16 20:23:43.406637 B 10 DataRow 1 0 2024-04-16 20:23:43.406642 B 13 CommandComplete SELECT 1 2024-04-16 20:23:43.406645 B 5 ReadyForQuery I 2024-04-16 20:23:43.406654 F 15 Close S p23456789 2024-04-16 20:23:43.406657 F 4 Sync 2024-04-16 20:23:43.406885 B 4 CloseComplete 2024-04-16 20:23:43.406928 B 5 ReadyForQuery I 2024-04-16 20:23:43.406938 F 4 Terminate [postgreslocalhost:/test/bin]$如上是通过直接调用libpq中的函数PQtrace和PQuntrace如下 // src/interfaces/libpq/fe-trace.c/* Enable tracing */ void PQtrace(PGconn *conn, FILE debug_port) {if (conn NULL)return;PQuntrace(conn);if (debug_port NULL)return;conn-Pfdebug debug_port;conn-traceFlags 0; }/ Disable tracing */ void PQuntrace(PGconn conn) {if (conn NULL)return;if (conn-Pfdebug){fflush(conn-Pfdebug);conn-Pfdebug NULL;}conn-traceFlags 0; }当然如上两函数是trace的开关函数真正实现打印的逻辑 如下 // src/interfaces/libpq/fe-trace.c/** Print the given message to the trace output stream. 将给定消息打印到跟踪输出流*/ void pqTraceOutputMessage(PGconn *conn, const char *message, bool toServer) {char id;int length;char prefix toServer ? F : B; // 这里指的是 Front / Backendint logCursor 0;bool regress;if ((conn-traceFlags PQTRACE_SUPPRESS_TIMESTAMPS) 0){char timestr[128];pqTraceFormatTimestamp(timestr, sizeof(timestr));fprintf(conn-Pfdebug, %s\t, timestr);}regress (conn-traceFlags PQTRACE_REGRESS_MODE) ! 0;id message[logCursor];memcpy(length, message logCursor, 4);length (int) pg_ntoh32(length);logCursor 4;/** In regress mode, suppress the length of ErrorResponse and NoticeResponse. The F (file name), L (line number) and R (routine* name) fields can change as server code is modified, and if their* lengths differ from the originals, that would break tests.* * 在回归模式下抑制ErrorResponse和NoticeResponse的长度* F文件名、L行号和 R例程名称字段可能会随着服务器代码的修改而更改* 如果它们的长度与原始长度不同则会破坏测试/if (regress !toServer (id E || id N))fprintf(conn-Pfdebug, %s\tNN\t, prefix);elsefprintf(conn-Pfdebug, %s\t%d\t, prefix, length);switch (id){case PqMsg_ParseComplete:fprintf(conn-Pfdebug, ParseComplete);/ No message content /break;case PqMsg_BindComplete:fprintf(conn-Pfdebug, BindComplete);/ No message content /break;case PqMsg_CloseComplete:fprintf(conn-Pfdebug, CloseComplete);/ No message content /break;case PqMsg_NotificationResponse:pqTraceOutputA(conn-Pfdebug, message, logCursor, regress);break;case PqMsg_Bind:pqTraceOutputB(conn-Pfdebug, message, logCursor);break;case PqMsg_CopyDone:fprintf(conn-Pfdebug, CopyDone);/ No message content /break;case PqMsg_CommandComplete:/ Close(F) and CommandComplete(B) use the same identifier. /Assert(PqMsg_Close PqMsg_CommandComplete);pqTraceOutputC(conn-Pfdebug, toServer, message, logCursor);break;case PqMsg_CopyData:/ Drop COPY data to reduce the overhead of logging. /break;case PqMsg_Describe:/ Describe(F) and DataRow(B) use the same identifier. /Assert(PqMsg_Describe PqMsg_DataRow);pqTraceOutputD(conn-Pfdebug, toServer, message, logCursor);break;case PqMsg_Execute:/ Execute(F) and ErrorResponse(B) use the same identifier. /Assert(PqMsg_Execute PqMsg_ErrorResponse);pqTraceOutputE(conn-Pfdebug, toServer, message, logCursor,regress);break;case PqMsg_CopyFail:pqTraceOutputf(conn-Pfdebug, message, logCursor);break;case PqMsg_FunctionCall:pqTraceOutputF(conn-Pfdebug, message, logCursor, regress);break;case PqMsg_CopyInResponse:pqTraceOutputG(conn-Pfdebug, message, logCursor);break;case PqMsg_Flush:/ Flush(F) and CopyOutResponse(B) use the same identifier /Assert(PqMsg_CopyOutResponse PqMsg_Flush);if (!toServer)pqTraceOutputH(conn-Pfdebug, message, logCursor);elsefprintf(conn-Pfdebug, Flush); / no message content /break;case PqMsg_EmptyQueryResponse:fprintf(conn-Pfdebug, EmptyQueryResponse);/ No message content /break;case PqMsg_BackendKeyData:pqTraceOutputK(conn-Pfdebug, message, logCursor, regress);break;case PqMsg_NoData:fprintf(conn-Pfdebug, NoData);/ No message content /break;case PqMsg_NoticeResponse:pqTraceOutputNR(conn-Pfdebug, NoticeResponse, message,logCursor, regress);break;case PqMsg_Parse:pqTraceOutputP(conn-Pfdebug, message, logCursor, regress);break;case PqMsg_Query:pqTraceOutputQ(conn-Pfdebug, message, logCursor);break;case PqMsg_AuthenticationRequest:pqTraceOutputR(conn-Pfdebug, message, logCursor);break;case PqMsg_PortalSuspended:fprintf(conn-Pfdebug, PortalSuspended);/ No message content /break;case PqMsg_Sync:/ Parameter Status(B) and Sync(F) use the same identifier /Assert(PqMsg_ParameterStatus PqMsg_Sync);if (!toServer)pqTraceOutputS(conn-Pfdebug, message, logCursor);elsefprintf(conn-Pfdebug, Sync); / no message content /break;case PqMsg_ParameterDescription:pqTraceOutputt(conn-Pfdebug, message, logCursor, regress);break;case PqMsg_RowDescription:pqTraceOutputT(conn-Pfdebug, message, logCursor, regress);break;case PqMsg_NegotiateProtocolVersion:pqTraceOutputv(conn-Pfdebug, message, logCursor);break;case PqMsg_FunctionCallResponse:pqTraceOutputV(conn-Pfdebug, message, logCursor);break;case PqMsg_CopyBothResponse:pqTraceOutputW(conn-Pfdebug, message, logCursor, length);break;case PqMsg_Terminate:fprintf(conn-Pfdebug, Terminate);/ No message content /break;case PqMsg_ReadyForQuery:pqTraceOutputZ(conn-Pfdebug, message, logCursor);break;default:fprintf(conn-Pfdebug, Unknown message: %02x, id);break;}fputc(\n, conn-Pfdebug);/** Verify the printing routine did it right. Note that the one-byte message identifier is not included in the length, but our cursor does* include it.* * 验证打印例程是否正确* 请注意一字节消息标识符不包括在长度中但我们的光标确实包括它/if (logCursor - 1 ! length)fprintf(conn-Pfdebug,mismatched message length: consumed %d, expected %d\n,logCursor - 1, length); }接下来我们重点看一下close消息的打印如下 pqTraceOutputMessage|pqTraceOutputC/ Close(F) or CommandComplete(B) */ static void pqTraceOutputC(FILE *f, bool toServer, const char *message, int cursor) {if (toServer){fprintf(f, Close\t);pqTraceOutputByte1(f, message, cursor);pqTraceOutputString(f, message, cursor, false);}else{fprintf(f, CommandComplete\t);pqTraceOutputString(f, message, cursor, false);} } /** pqTraceOutputByte1: output a 1-char message to the log pqTraceOutputByte1将 1 个字符的消息输出到日志*/ static void pqTraceOutputByte1(FILE *pfdebug, const char *data, int *cursor) {const char *v data cursor;/** Show non-printable data in hex format, including the terminating \0 that completes ErrorResponse and NoticeResponse messages.* * 以十六进制格式显示不可打印的数据* 包括完成ErrorResponse 和NoticeResponse 消息的终止\0*/if (!isprint((unsigned char) *v))fprintf(pfdebug, \x%02x, *v);elsefprintf(pfdebug, %c, *v);cursor 1; }/** pqTraceOutputString: output a string message to the log pqTraceOutputString输出字符串消息到日志*/ static void pqTraceOutputString(FILE *pfdebug, const char *data, int *cursor, bool suppress) {int len;if (suppress){fprintf(pfdebug, \SSSS);*cursor strlen(data *cursor) 1;}else{len fprintf(pfdebug, \%s\, data cursor);/** This is a null-terminated string. So add 1 after subtracting 3 which is the double quotes and space length from len.* * 这是一个以 null 结尾的字符串* 因此从 len 中减去双引号和空格长度 3 后加 1*/*cursor (len - 3 1);} }接下来我们继续以close消息为例详细看一下message的构造和解析过程

len 152024-04-16 20:23:43.406654 F 15 Close S p23456789前端信息构造

此时的函数堆栈如下 libpq.so.5!PQsendTypedCommand(PGconn * conn, char command, char type, const char * target) (\home\postgres\postgres\src\interfaces\libpq\fe-exec.c:2605) libpq.so.5!PQsendClosePrepared(PGconn * conn, const char * stmt) (\home\postgres\postgres\src\interfaces\libpq\fe-exec.c:2558) main() (\home\postgres\test\bin\libpqtest2.cpp:110)接下来就详细看一下这里的处理逻辑如下 第一步 // src/interfaces/libpq/fe-exec.c/** pqPutMsgStart: begin construction of a message to the server* pqPutMsgStart开始向服务器构造消息** msg_type is the message type byte, or 0 for a message without type byte* (only startup messages have no type byte)* msg_type 是消息类型字节如果没有类型字节则为 0只有启动消息没有类型字节** Returns 0 on success, EOF on error* 成功时返回 0错误时返回 EOF** The idea here is that we construct the message in conn-outBuffer,* beginning just past any data already in outBuffer (ie, at* outBufferoutCount). We enlarge the buffer as needed to hold the message.* When the message is complete, we fill in the length word (if needed) and* then advance outCount past the message, making it eligible to send.* 这里的想法是我们在 conn-outBuffer 中构造消息从 outBuffer 中已有的任何数据开始即在 outBufferoutCount 处* 我们根据需要扩大缓冲区来保存消息* 消息完成后我们填写长度字如果需要然后将 outCount 提前到消息后面使其符合发送条件** The state variable conn-outMsgStart points to the incomplete messages* length word: it is either outCount or outCount1 depending on whether* there is a type byte. The state variable conn-outMsgEnd is the end of* the data collected so far.* 状态变量 conn-outMsgStart 指向不完整消息的长度字* 它是 outCount 或 outCount1具体取决于是否存在类型字节* 状态变量 conn-outMsgEnd 是迄今为止收集的数据的结尾*/ int pqPutMsgStart(char msg_type, PGconn conn) {int lenPos;int endPos;/ allow room for message type byte /if (msg_type)endPos conn-outCount 1;elseendPos conn-outCount;/ do we want a length word? /lenPos endPos;/ allow room for message length /endPos 4;/ make sure there is room for message header /if (pqCheckOutBufferSpace(endPos, conn))return EOF;/ okay, save the message type byte if any /if (msg_type)conn-outBuffer[conn-outCount] msg_type;/ set up the message pointers /conn-outMsgStart lenPos;conn-outMsgEnd endPos;/ length word, if needed, will be filled in by pqPutMsgEnd */return 0; }解释一下 msg_type此时是 CendPos 4; 就代表了 已经把消息长度的空间分配好了conn-outCount 0conn-outBuffer[conn-outCount] msg_type; // 放的就是 Cconn-outMsgStart 1conn-outMsgEnd 5 第二步 libpq.so.5!pqPutMsgBytes(const void * buf, size_t len, PGconn * conn) (\home\postgres\postgres\src\interfaces\libpq\fe-misc.c:497) libpq.so.5!pqPutc(char c, PGconn * conn) (\home\postgres\postgres\src\interfaces\libpq\fe-misc.c:94) libpq.so.5!PQsendTypedCommand(PGconn * conn, char command, char type, const char * target) (\home\postgres\postgres\src\interfaces\libpq\fe-exec.c:2606) libpq.so.5!PQsendClosePrepared(PGconn * conn, const char * stmt) (\home\postgres\postgres\src\interfaces\libpq\fe-exec.c:2558) main() (\home\postgres\test\bin\libpqtest2.cpp:110)/** pqPutc: write 1 char to the current message*/ int pqPutc(char c, PGconn conn) {if (pqPutMsgBytes(c, 1, conn))return EOF;return 0; }…/** pqPutMsgBytes: add bytes to a partially-constructed message pqPutMsgBytes向部分构造的消息添加字节** Returns 0 on success, EOF on error*/ static int pqPutMsgBytes(const void *buf, size_t len, PGconn conn) {/ make sure there is room for it /if (pqCheckOutBufferSpace(conn-outMsgEnd len, conn))return EOF;/ okay, save the data /memcpy(conn-outBuffer conn-outMsgEnd, buf, len);conn-outMsgEnd len;/ no Pfdebug call here, caller should do it */return 0; }解释一下 因为 type 是’S’因此这里写的就是它因为内存copy是从 conn-outBuffer conn-outMsgEnd 开始的也就放到了conn-outBuffer[5]conn-outMsgEnd 1 第三步 libpq.so.5!pqPutMsgBytes(const void * buf, size_t len, PGconn * conn) (\home\postgres\postgres\src\interfaces\libpq\fe-misc.c:500) libpq.so.5!pqPuts(const char * s, PGconn * conn) (\home\postgres\postgres\src\interfaces\libpq\fe-misc.c:154) libpq.so.5!PQsendTypedCommand(PGconn * conn, char command, char type, const char * target) (\home\postgres\postgres\src\interfaces\libpq\fe-exec.c:2607) libpq.so.5!PQsendClosePrepared(PGconn * conn, const char * stmt) (\home\postgres\postgres\src\interfaces\libpq\fe-exec.c:2558) main() (\home\postgres\test\bin\libpqtest2.cpp:110)/** pqPuts: write a null-terminated string to the current message* pqPuts将空终止字符串写入当前消息*/ int pqPuts(const char *s, PGconn *conn) {if (pqPutMsgBytes(s, strlen(s) 1, conn))return EOF;return 0; }解释一下 len strlen 1; strlen(“p23456789”) 1 10内存copy是从 conn-outMsgEnd 6 开始的len 10。自然结果如上conn-outMsgEnd 10 第四步 libpq.so.5!pqPutMsgEnd(PGconn * conn) (\home\postgres\postgres\src\interfaces\libpq\fe-misc.c:520) libpq.so.5!PQsendTypedCommand(PGconn * conn, char command, char type, const char * target) (\home\postgres\postgres\src\interfaces\libpq\fe-exec.c:2608) libpq.so.5!PQsendClosePrepared(PGconn * conn, const char * stmt) (\home\postgres\postgres\src\interfaces\libpq\fe-exec.c:2558) main() (\home\postgres\test\bin\libpqtest2.cpp:110)/** pqPutMsgEnd: finish constructing a message and possibly send it* pqPutMsgEnd完成构建消息并可能发送它** Returns 0 on success, EOF on error** We dont actually send anything here unless weve accumulated at least* 8K worth of data (the typical size of a pipe buffer on Unix systems).* This avoids sending small partial packets. The caller must use pqFlush* when its important to flush all the data out to the server.* * 除非我们已经积累了至少 8K 的数据Unix 系统上管道缓冲区的典型大小否则我们实际上不会在这里发送任何内容* 这避免了发送小部分数据包* 当需要将所有数据刷新到服务器时调用者必须使用 pqFlush*/ int pqPutMsgEnd(PGconn conn) {/ Fill in length word if needed /if (conn-outMsgStart 0){uint32 msgLen conn-outMsgEnd - conn-outMsgStart;msgLen pg_hton32(msgLen);memcpy(conn-outBuffer conn-outMsgStart, msgLen, 4);}/ trace client-to-server message /if (conn-Pfdebug){if (conn-outCount conn-outMsgStart)pqTraceOutputMessage(conn, conn-outBuffer conn-outCount, true);elsepqTraceOutputNoTypeByteMessage(conn,conn-outBuffer conn-outMsgStart);}/ Make message eligible to send /conn-outCount conn-outMsgEnd;if (conn-outCount 8192){int toSend conn-outCount - (conn-outCount % 8192);if (pqSendSome(conn, toSend) 0)return EOF;/ in nonblock mode, dont complain if unable to send it all */}return 0; }解释一下 如上 message_len 16 - 1 15然后大端存储内存copy是从 conn-outMsgStart 1开始长度是4 自然就是上面的四字节conn-outCount conn-outMsgEnd 16 至此该15字节的close消息构建完毕 后端消息解析 我们这里调试服务进程如下 第一步消息读取如下 pq_recvbuf() (\home\postgres\postgres\src\backend\libpq\pqcomm.c:926) pq_getbyte() (\home\postgres\postgres\src\backend\libpq\pqcomm.c:969) SocketBackend(StringInfo inBuf) (\home\postgres\postgres\src\backend\tcop\postgres.c:370) ReadCommand(StringInfo inBuf) (\home\postgres\postgres\src\backend\tcop\postgres.c:493) PostgresMain(const char * dbname, const char * username) (\home\postgres\postgres\src\backend\tcop\postgres.c:4612) BackendMain(char * startup_data, size_t startup_data_len) (\home\postgres\postgres\src\backend\tcop\backend_startup.c:105) postmaster_child_launch(BackendType child_type, char * startup_data, size_t startup_data_len, ClientSocket * client_sock) (\home\postgres\postgres\src\backend\postmaster\launch_backend.c:265) BackendStartup(ClientSocket * client_sock) (\home\postgres\postgres\src\backend\postmaster\postmaster.c:3593) ServerLoop() (\home\postgres\postgres\src\backend\postmaster\postmaster.c:1674) PostmasterMain(int argc, char ** argv) (\home\postgres\postgres\src\backend\postmaster\postmaster.c:1372) main(int argc, char ** argv) (\home\postgres\postgres\src\backend\main\main.c:197)// src/backend/libpq/pqcomm.c/* ——————————–* pq_recvbuf - load some bytes into the input buffer* pq_recvbuf - 将一些字节加载到输入缓冲区中** returns 0 if OK, EOF if trouble* ——————————–/ static int pq_recvbuf(void) {if (PqRecvPointer 0){if (PqRecvLength PqRecvPointer){/ still some unread data, left-justify it in the buffer /// 还有一些未读数据将其在缓冲区中左对齐memmove(PqRecvBuffer, PqRecvBuffer PqRecvPointer,PqRecvLength - PqRecvPointer);PqRecvLength - PqRecvPointer;PqRecvPointer 0;}elsePqRecvLength PqRecvPointer 0;}/ Ensure that were in blocking mode /// 确保我们处于阻塞模式socket_set_nonblocking(false);/ Can fill buffer from PqRecvLength and upwards /// 可以从 PqRecvLength 及以上填充缓冲区for (;;){int r;errno 0;r secure_read(MyProcPort, PqRecvBuffer PqRecvLength,PQ_RECV_BUFFER_SIZE - PqRecvLength);if (r 0){if (errno EINTR)continue; / Ok if interrupted //** Careful: an ereport() that tries to write to the client would cause recursion to here, leading to stack overflow and core* dump! This message must go only to the postmaster log.* 小心尝试写入客户端的 ereport() 会导致递归到此处从而导致堆栈溢出和核心转储* 此消息必须 仅 发送到邮件管理员日志** If errno is zero, assume its EOF and let the caller complain.* 如果 errno 为零则假设它是 EOF 并让调用者抱怨/if (errno ! 0)ereport(COMMERROR,(errcode_for_socket_access(),errmsg(could not receive data from client: %m)));return EOF;}if (r 0){/** EOF detected. We used to write a log message here, but its better to expect the ultimate caller to do that.* 检测到 EOF* 我们曾经在这里编写日志消息但最好期望最终调用者这样做/return EOF;}/ r contains number of bytes read, so just incr length /// r 包含读取的字节数因此只需增加长度PqRecvLength r;return 0;} }解释一下 PqRecvLength 21 这个其实是两条消息 如下 / construct the Close message / // 0 - 15if (pqPutMsgStart(command, conn) 0 ||pqPutc(type, conn) 0 ||pqPuts(target, conn) 0 ||pqPutMsgEnd(conn) 0)goto sendFailed;/ construct the Sync message / // 16 - 20if (conn-pipelineStatus PQ_PIPELINE_OFF){if (pqPutMsgStart(PqMsg_Sync, conn) 0 ||pqPutMsgEnd(conn) 0)goto sendFailed;}第二步 / ——————————–* pq_getbyte - get a single byte from connection, or return EOF* ——————————–/ int pq_getbyte(void) {Assert(PqCommReadingMsg);while (PqRecvPointer PqRecvLength){if (pq_recvbuf()) / If nothing in buffer, then recv some /return EOF; / Failed to recv data /}return (unsigned char) PqRecvBuffer[PqRecvPointer]; }解释一下 此时 PqRecvPointer 0自然返回的是 C 第三步 …/** In protocol version 3, all frontend messages have a length word next after the type code; we can read the message contents independently of* the type.* * 在协议版本 3 中所有前端消息在类型代码之后都有一个长度字* 我们可以独立于类型来读取消息内容/if (pq_getmessage(inBuf, maxmsglen))return EOF; / suitable message already logged /RESUME_CANCEL_INTERRUPTS(); …/ ——————————–* pq_getmessage - get a message with length word from connection* pq_getmessage - 从连接获取长度字的消息** The return value is placed in an expansible StringInfo, which has* already been initialized by the caller.* Only the message body is placed in the StringInfo; the length word* is removed. Also, s-cursor is initialized to zero for convenience* in scanning the message contents.* 返回值放置在可扩展的 StringInfo 中该 StringInfo 已由调用者初始化* StringInfo中只放置消息体 长度词被删除* 另外为了方便扫描消息内容s-cursor 被初始化为零** maxlen is the upper limit on the length of the* message we are willing to accept. We abort the connection (by* returning EOF) if client tries to send more than that.* maxlen 是我们愿意接受的消息长度的上限* 如果客户端尝试发送更多内容我们将中止连接通过返回 EOF** returns 0 if OK, EOF if trouble* ——————————–/ int pq_getmessage(StringInfo s, int maxlen) {int32 len;Assert(PqCommReadingMsg);resetStringInfo(s);/ Read message length word */if (pq_getbytes((char ) len, 4) EOF){ereport(COMMERROR,(errcode(ERRCODE_PROTOCOL_VIOLATION),errmsg(unexpected EOF within message length word)));return EOF;}len pg_ntoh32(len);if (len 4 || len maxlen){ereport(COMMERROR,(errcode(ERRCODE_PROTOCOL_VIOLATION),errmsg(invalid message length)));return EOF;}len - 4; / discount length itself /if (len 0){/** Allocate space for message. If we run out of room (ridiculously large message), we will elog(ERROR), but we want to discard the* message body so as not to lose communication sync./PG_TRY();{enlargeStringInfo(s, len);}PG_CATCH();{if (pq_discardbytes(len) EOF)ereport(COMMERROR,(errcode(ERRCODE_PROTOCOL_VIOLATION),errmsg(incomplete message from client)));/ we discarded the rest of the message so were back in sync. /PqCommReadingMsg false;PG_RE_THROW();}PG_END_TRY();/ And grab the message /if (pq_getbytes(s-data, len) EOF){ereport(COMMERROR,(errcode(ERRCODE_PROTOCOL_VIOLATION),errmsg(incomplete message from client)));return EOF;}s-len len;/ Place a trailing null per StringInfo convention /s-data[len] \0;}/ finished reading the message. /PqCommReadingMsg false;return 0; }解释一下 读取长度 4字节memcpy(s, PqRecvBuffer PqRecvPointer, amount);此时 PqRecvPointer 1pg_ntoh32 网络序–主机序 len 15len - 4; / discount length itself */读取长度 11 字节memcpy(s, PqRecvBuffer PqRecvPointer, amount);此时 PqRecvPointer 5此时读取的内容0x1e54c88 Sp23456789也就是 input_message 接下来ReadCommand的结果如下 firstchar ReadCommand(input_message); // C最后一步如下 OK至此 服务端解析完毕