PostgreSQL中的ProcessRepliesIfAny函数分析

本篇内容主要讲解"PostgreSQL中的ProcessRepliesIfAny函数分析"，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习"PostgreSQL中的ProcessRepliesIfAny函数分析"吧!

调用栈如下:

(gdb) bt#0  0x00007fb6e6390903 in __epoll_wait_nocancel () from /lib64/libc.so.6#1  0x000000000088e668 in WaitEventSetWaitBlock (set=0x10ac808, cur_timeout=29999, occurred_events=0x7ffd634441b0,     nevents=1) at latch.c:1048#2  0x000000000088e543 in WaitEventSetWait (set=0x10ac808, timeout=29999, occurred_events=0x7ffd634441b0, nevents=1,     wait_event_info=83886092) at latch.c:1000#3  0x000000000088dcec in WaitLatchOrSocket (latch=0x7fb6dcbfc4d4, wakeEvents=27, sock=10, timeout=29999,     wait_event_info=83886092) at latch.c:385#4  0x000000000085405b in WalSndLoop (send_data=0x8547fe ) at walsender.c:2229#5  0x0000000000851c93 in StartReplication (cmd=0x10ab750) at walsender.c:684#6  0x00000000008532f0 in exec_replication_command (cmd_string=0x101dd78 "START_REPLICATION 0/5D000000 TIMELINE 16")    at walsender.c:1539#7  0x00000000008c0170 in PostgresMain (argc=1, argv=0x1049cb8, dbname=0x1049ba8 "", username=0x1049b80 "replicator")    at postgres.c:4178#8  0x000000000081e06c in BackendRun (port=0x103fb50) at postmaster.c:4361#9  0x000000000081d7df in BackendStartup (port=0x103fb50) at postmaster.c:4033#10 0x0000000000819bd9 in ServerLoop () at postmaster.c:1706#11 0x000000000081948f in PostmasterMain (argc=1, argv=0x1018a50) at postmaster.c:1379#12 0x0000000000742931 in main (argc=1, argv=0x1018a50) at main.c:228

一、数据结构

N/A

二、源码解读

ProcessRepliesIfAny
在streaming期间,处理接收到的消息,同时检查远程终端是否关闭了连接,执行相关处理.
代码不多也不复杂,可自行阅读.

/* * Process any incoming messages while streaming. Also checks if the remote * end has closed the connection. * 在streaming期间,处理接收到的消息. * 同时检查远程终端是否关闭了连接,执行相关处理. */static voidProcessRepliesIfAny(void){    unsigned char firstchar;    int         r;    bool        received = false;    //当前时间    last_processing = GetCurrentTimestamp();    for (;;)    {        //---------- 循环接收相关消息        pq_startmsgread();        r = pq_getbyte_if_available(&firstchar);        if (r < 0)        {            /* unexpected error or EOF */            //未知异常或者EOF            ereport(COMMERROR,                    (errcode(ERRCODE_PROTOCOL_VIOLATION),                     errmsg("unexpected EOF on standby connection")));            //进程退出            proc_exit(0);        }        if (r == 0)        {            /* no data available without blocking */            //已无阻塞的消息数据,退出            pq_endmsgread();            break;        }        /* Read the message contents */        //读取消息内容        resetStringInfo(&reply_message);        if (pq_getmessage(&reply_message, 0))        {            ereport(COMMERROR,                    (errcode(ERRCODE_PROTOCOL_VIOLATION),                     errmsg("unexpected EOF on standby connection")));            proc_exit(0);        }        /*         * If we already received a CopyDone from the frontend, the frontend         * should not send us anything until we've closed our end of the COPY.         * XXX: In theory, the frontend could already send the next command         * before receiving the CopyDone, but libpq doesn't currently allow         * that.         * 如果已在前台接收到CopyDone消息,前台不应该再发送消息,直至关闭COPY.         * XXX:理论上来说,在接收到CopyDone前,前台可能已经发送了下一个命令,但libpq不允许这种情况发生         */        if (streamingDoneReceiving && firstchar != 'X')            ereport(FATAL,                    (errcode(ERRCODE_PROTOCOL_VIOLATION),                     errmsg("unexpected standby message type \"%c\", after receiving CopyDone",                            firstchar)));        /* Handle the very limited subset of commands expected in this phase */        //处理有限几个命令        switch (firstchar)        {                /*                 * 'd' means a standby reply wrapped in a CopyData packet.                 * 'd'意味着standby节点的应答封装了CopyData包                 */            case 'd':                ProcessStandbyMessage();                received = true;                break;                /*                 * CopyDone means the standby requested to finish streaming.                 * Reply with CopyDone, if we had not sent that already.                 * CopyDone意味着standby节点请求结束streaming.                 * 如尚未发送,则使用CopyDone应答.                 */            case 'c':                if (!streamingDoneSending)                {                    pq_putmessage_noblock('c', NULL, 0);                    streamingDoneSending = true;                }                streamingDoneReceiving = true;                received = true;                break;                /*                 * 'X' means that the standby is closing down the socket.                 * 'X'意味着standby节点正在关闭socket                 */            case 'X':                proc_exit(0);            default:                ereport(FATAL,                        (errcode(ERRCODE_PROTOCOL_VIOLATION),                         errmsg("invalid standby message type \"%c\"",                                firstchar)));        }    }    /*     * Save the last reply timestamp if we've received at least one reply.     * 如接收到至少一条应答信息,则保存最后的应答时间戳.     */    if (received)    {        last_reply_timestamp = last_processing;        waiting_for_ping_response = false;    }}

二、跟踪分析

在主节点上用gdb跟踪postmaster,在PostgresMain上设置断点后启动standby节点,进入断点

(gdb) set follow-fork-mode child(gdb) b ProcessRepliesIfAnyBreakpoint 2 at 0x85343b: file walsender.c, line 1597.(gdb) cContinuing.Breakpoint 2, ProcessRepliesIfAny () at walsender.c:15971597        bool        received = false;(gdb)

查看进程信息

[xdb@localhost ~]$ ps -ef|grep postgresxdb       1376     1  0 14:16 ?        00:00:00 /appdb/xdb/pg11.2/bin/postgresxdb       1377  1376  0 14:16 ?        00:00:00 postgres: logger   xdb       1550  1376  0 16:53 ?        00:00:00 postgres: checkpointer   xdb       1551  1376  0 16:53 ?        00:00:00 postgres: background writer   xdb       1552  1376  0 16:53 ?        00:00:00 postgres: walwriter   xdb       1553  1376  0 16:53 ?        00:00:00 postgres: autovacuum launcher  xdb       1554  1376  0 16:53 ?        00:00:00 postgres: archiver   xdb       1555  1376  0 16:53 ?        00:00:00 postgres: stats collector   xdb       1556  1376  0 16:53 ?        00:00:00 postgres: logical replication launcher  xdb       1633  1376  0 17:26 ?        00:00:00 postgres: walsender replicator 192.168.26.26(40528) idle

循环接收相关消息

(gdb) n1599        last_processing = GetCurrentTimestamp();(gdb) 1603            pq_startmsgread();(gdb) 1604            r = pq_getbyte_if_available(&firstchar);(gdb) 1605            if (r < 0)(gdb) p r$1 = 1(gdb) p firstchar$2 = 100 'd'(gdb)

命令是'd',执行相关处理

(gdb) n1613            if (r == 0)(gdb) 1621            resetStringInfo(&reply_message);(gdb) 1622            if (pq_getmessage(&reply_message, 0))(gdb) 1637            if (streamingDoneReceiving && firstchar != 'X')(gdb) 1644            switch (firstchar)(gdb) 1650                    ProcessStandbyMessage();(gdb) 1651                    received = true;(gdb) 1652                    break;(gdb) 1681        }(gdb)

设置断点

(gdb) b walsender.c:1643Breakpoint 3 at 0x8535b6: file walsender.c, line 1643.(gdb) b walsender.c:1672Breakpoint 4 at 0x85361a: file walsender.c, line 1672.(gdb) cContinuing.Breakpoint 3, ProcessRepliesIfAny () at walsender.c:16441644            switch (firstchar)(gdb) Continuing....Breakpoint 4, ProcessRepliesIfAny () at walsender.c:16731673                    proc_exit(0);(gdb)

进程即将退出,查看进程信息

[xdb@localhost ~]$ ps -ef|grep postgresxdb       1376     1  0 14:16 ?        00:00:00 /appdb/xdb/pg11.2/bin/postgresxdb       1377  1376  0 14:16 ?        00:00:00 postgres: logger   xdb       1550  1376  0 16:53 ?        00:00:00 postgres: checkpointer   xdb       1551  1376  0 16:53 ?        00:00:00 postgres: background writer   xdb       1552  1376  0 16:53 ?        00:00:00 postgres: walwriter   xdb       1553  1376  0 16:53 ?        00:00:00 postgres: autovacuum launcher  xdb       1554  1376  0 16:53 ?        00:00:00 postgres: archiver   xdb       1555  1376  0 16:53 ?        00:00:00 postgres: stats collector   xdb       1556  1376  0 16:53 ?        00:00:00 postgres: logical replication launcher  xdb       1633  1376  0 17:26 ?        00:00:00 postgres: walsender replicator 192.168.26.26(40528) idlexdb       1637  1376  0 17:27 ?        00:00:00 postgres: walsender replicator 192.168.26.26(40530) streaming 0/5D075248[xdb@localhost ~]$

进程退出(PID=1633),启动了新的进程(PID=1637)

(gdb) n[Inferior 2 (process 1633) exited normally](gdb)

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