本篇内容主要讲解“PostgreSQL中StartLogStreamer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StartLogStreamer分析”吧!
本节简单介绍了PostgreSQL的备份工具pg_basebackup源码中实际执行备份逻辑的BaseBackup中对WAL数据进行备份的实现函数StartLogStreamer.
一、数据结构
logstreamer_param
WAL data streamer参数.
typedef struct
{
////后台连接
PGconn *bgconn;
//开始位置
XLogRecPtr startptr;
//目录或者tar文件,依赖于使用的模式
char xlog[MAXPGPATH];
//系统标识符
char *sysidentifier;
//时间线
int timeline;
} logstreamer_param;StreamCtl
接收xlog流数据时的全局参数
typedef struct StreamCtl
{
//streaming的开始位置
XLogRecPtr startpos;
//时间线
TimeLineID timeline;
//系统标识符
char *sysidentifier;
//standby超时信息
int standby_message_timeout;
//是否同步(写入时是否马上Flush WAL data)
bool synchronous;
//在已归档的数据中标记segment为已完成
bool mark_done;
//刷新到磁盘上以确保数据的一致性状态(是否已刷新到磁盘上)
bool do_sync;
//在返回T时停止streaming
stream_stop_callback stream_stop;
//如有效,监测该socket中的输入并检查stream_stop()的返回
pgsocket stop_socket;
//如何写WAL
WalWriteMethod *walmethod;
//附加到部分接受文件的后缀
char *partial_suffix;
//使用的replication slot,如无则为NULL
char *replication_slot;
} StreamCtl;二、源码解读
StartLogStreamer
StartLogStreamer用于在备份时初始化后台进程用于接收WAL.接收进程将创建自己的数据库连接以并行的方式对文件进行streaming复制.
static void
StartLogStreamer(char *startpos, uint32 timeline, char *sysidentifier)
{
//参数
logstreamer_param *param;
uint32 hi,
lo;//高位/低位
char statusdir[MAXPGPATH];
param = pg_malloc0(sizeof(logstreamer_param));
param->timeline = timeline;
param->sysidentifier = sysidentifier;
//转换开始位置(高低位转换)
if (sscanf(startpos, "%X/%X", &hi, &lo) != 2)
{
fprintf(stderr,
_("%s: could not parse write-ahead log location \"%s\"\n"),
progname, startpos);
exit(1);
}
//开始位置,转换为64bit的地址
param->startptr = ((uint64) hi) << 32 | lo;
//按segment取整
param->startptr -= XLogSegmentOffset(param->startptr, WalSegSz);
#ifndef WIN32
//WIN32使用的代码
if (pipe(bgpipe) < 0)
{
fprintf(stderr,
_("%s: could not create pipe for background process: %s\n"),
progname, strerror(errno));
exit(1);
}
#endif
//获取第二个连接
param->bgconn = GetConnection();
if (!param->bgconn)
exit(1);
//在PG 10,pg_xlog已命名为pg_wal
snprintf(param->xlog, sizeof(param->xlog), "%s/%s",
basedir,
PQserverVersion(conn) < MINIMUM_VERSION_FOR_PG_WAL ?
"pg_xlog" : "pg_wal");
//临时复制slots只在PG10+支持
if (PQserverVersion(conn) < MINIMUM_VERSION_FOR_TEMP_SLOTS)
temp_replication_slot = false;
//static char *replication_slot = NULL;
//static bool temp_replication_slot = true;
if (temp_replication_slot && !replication_slot)
//创建replication slot
replication_slot = psprintf("pg_basebackup_%d", (int) PQbackendPID(param->bgconn));
if (temp_replication_slot || create_slot)
{
//创建replication slot
if (!CreateReplicationSlot(param->bgconn, replication_slot, NULL,
temp_replication_slot, true, true, false))
exit(1);
if (verbose)
{
//显示诊断信息
if (temp_replication_slot)
fprintf(stderr, _("%s: created temporary replication slot \"%s\"\n"),
progname, replication_slot);
else
fprintf(stderr, _("%s: created replication slot \"%s\"\n"),
progname, replication_slot);
}
}
if (format == 'p')
{
snprintf(statusdir, sizeof(statusdir), "%s/%s/archive_status",
basedir,
PQserverVersion(conn) < MINIMUM_VERSION_FOR_PG_WAL ?
"pg_xlog" : "pg_wal");
if (pg_mkdir_p(statusdir, pg_dir_create_mode) != 0 && errno != EEXIST)
{
fprintf(stderr,
_("%s: could not create directory \"%s\": %s\n"),
progname, statusdir, strerror(errno));
exit(1);
}
}
#ifndef WIN32
//UNIX:fork进程
bgchild = fork();
if (bgchild == 0)
{
//这是子进程,返回0
//启动新进程
exit(LogStreamerMain(param));
}
else if (bgchild < 0)
{
fprintf(stderr, _("%s: could not create background process: %s\n"),
progname, strerror(errno));
exit(1);
}
atexit(kill_bgchild_atexit);
#else
//WIN32:创建线程
bgchild = _beginthreadex(NULL, 0, (void *) LogStreamerMain, param, 0, NULL);
if (bgchild == 0)
{
fprintf(stderr, _("%s: could not create background thread: %s\n"),
progname, strerror(errno));
exit(1);
}
#endif
}LogStreamerMain
WAL流复制主函数,用于fork后的子进程调用
static int
LogStreamerMain(logstreamer_param *param)
{
StreamCtl stream;//接收xlog流数据时的全局参数
in_log_streamer = true;
//初始化StreamCtl结构体
MemSet(&stream, 0, sizeof(stream));
stream.startpos = param->startptr;
stream.timeline = param->timeline;
stream.sysidentifier = param->sysidentifier;
stream.stream_stop = reached_end_position;
#ifndef WIN32
stream.stop_socket = bgpipe[0];
#else
stream.stop_socket = PGINVALID_SOCKET;
#endif
stream.standby_message_timeout = standby_message_timeout;
stream.synchronous = false;
stream.do_sync = do_sync;
stream.mark_done = true;
stream.partial_suffix = NULL;
stream.replication_slot = replication_slot;
if (format == 'p')
stream.walmethod = CreateWalDirectoryMethod(param->xlog, 0, do_sync);
else
stream.walmethod = CreateWalTarMethod(param->xlog, compresslevel, do_sync);
//接收数据
if (!ReceiveXlogStream(param->bgconn, &stream))
return 1;
if (!stream.walmethod->finish())
{
fprintf(stderr,
_("%s: could not finish writing WAL files: %s\n"),
progname, strerror(errno));
return 1;
}
//结束连接
PQfinish(param->bgconn);
//普通文件格式
if (format == 'p')
FreeWalDirectoryMethod();
else
FreeWalTarMethod();
//是否内存
pg_free(stream.walmethod);
return 0;
}三、跟踪分析
备份命令
pg_basebackup -h 192.168.26.25 -U replicator -p 5432 -D /data/backup -P -Xs -R -v启动gdb跟踪
[xdb@localhost ~]$ gdb pg_basebackup
GNU gdb (GDB) Red Hat Enterprise Linux 7.6.1-110.el7
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /appdb/atlasdb/pg11.2/bin/pg_basebackup...done.
(gdb) b StartLogStreamer
Breakpoint 1 at 0x403e6b: file pg_basebackup.c, line 555.
(gdb) set args -h 192.168.26.25 -U replicator -p 5432 -D /data/backup -P -Xs -R -v
(gdb) r
Starting program: /appdb/xdb/pg11.2/bin/pg_basebackup -h 192.168.26.25 -U replicator -p 5432 -D /data/backup -P -Xs -R -v
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
Password:
pg_basebackup: initiating base backup, waiting for checkpoint to complete
pg_basebackup: checkpoint completed
pg_basebackup: write-ahead log start point: 0/57000060 on timeline 16
pg_basebackup: starting background WAL receiver
Breakpoint 1, StartLogStreamer (startpos=0x7fffffffdf60 "0/57000060", timeline=16,
sysidentifier=0x61f1a0 "6666964067616600474") at pg_basebackup.c:555
555 param = pg_malloc0(sizeof(logstreamer_param));
(gdb)输入参数
startpos=0x7fffffffdf60 “0/57000060”,
timeline=16,
sysidentifier=0x61f1a0 “6666964067616600474”
构造参数
(gdb) n
556 param->timeline = timeline;
(gdb)
557 param->sysidentifier = sysidentifier;
(gdb)
560 if (sscanf(startpos, "%X/%X", &hi, &lo) != 2)
(gdb)
567 param->startptr = ((uint64) hi) << 32 | lo;
(gdb) p hi
$1 = 0
(gdb) p lo
$2 = 1459617888
(gdb) n
569 param->startptr -= XLogSegmentOffset(param->startptr, WalSegSz);
(gdb) n
573 if (pipe(bgpipe) < 0)
(gdb) p *param
$3 = {bgconn = 0x0, startptr = 1459617792, xlog = '\000' <repeats 1023 times>,
sysidentifier = 0x61f1a0 "6666964067616600474", timeline = 16}
(gdb)建立连接,创建replication slot
(gdb) n
583 param->bgconn = GetConnection();
(gdb)
584 if (!param->bgconn)
(gdb)
591 PQserverVersion(conn) < MINIMUM_VERSION_FOR_PG_WAL ?
(gdb)
589 snprintf(param->xlog, sizeof(param->xlog), "%s/%s",
(gdb)
595 if (PQserverVersion(conn) < MINIMUM_VERSION_FOR_TEMP_SLOTS)
(gdb)
601 if (temp_replication_slot && !replication_slot)
(gdb)
602 replication_slot = psprintf("pg_basebackup_%d", (int) PQbackendPID(param->bgconn));
(gdb)
603 if (temp_replication_slot || create_slot)
(gdb)
605 if (!CreateReplicationSlot(param->bgconn, replication_slot, NULL,
(gdb)
609 if (verbose)
(gdb)
611 if (temp_replication_slot)
(gdb)
612 fprintf(stderr, _("%s: created temporary replication slot \"%s\"\n"),
(gdb)
pg_basebackup: created temporary replication slot "pg_basebackup_59378"
620 if (format == 'p')
(gdb)
(gdb) n
630 PQserverVersion(conn) < MINIMUM_VERSION_FOR_PG_WAL ?
(gdb)
628 snprintf(statusdir, sizeof(statusdir), "%s/%s/archive_status",创建备份目录
(gdb)
633 if (pg_mkdir_p(statusdir, pg_dir_create_mode) != 0 && errno != EEXIST)
(gdb) p *param
$4 = {bgconn = 0x62a280, startptr = 1459617792, xlog = "/data/backup/pg_wal", '\000' <repeats 1004 times>,
sysidentifier = 0x61f1a0 "6666964067616600474", timeline = 16}
(gdb) n
647 bgchild = fork();
(gdb)
#############
[xdb@localhost backup]$ ls
pg_walfork进程,父进程返回子进程的PID
(gdb) n
647 bgchild = fork();
(gdb) n
Detaching after fork from child process 43001.
648 if (bgchild == 0)
(gdb) p bgchild
$5 = 43001
(gdb)子进程(PID=43001)
[xdb@localhost backup]$ ps -ef|grep 43001
xdb 43001 42820 1 11:54 pts/1 00:00:01 /appdb/xdb/pg11.2/bin/pg_basebackup -h 192.168.26.25 -U replicator -p 5432 -D /data/backup -P -Xs -R -v
[xdb@localhost backup]$ ps -ef|grep 192.168.26.25
xdb 42820 42756 0 11:48 pts/1 00:00:00 /appdb/xdb/pg11.2/bin/pg_basebackup -h 192.168.26.25 -U replicator -p 5432 -D /data/backup -P -Xs -R -v
xdb 43001 42820 0 11:54 pts/1 00:00:01 /appdb/xdb/pg11.2/bin/pg_basebackup -h 192.168.26.25 -U replicator -p 5432 -D /data/backup -P -Xs -R -v完成调用
(gdb) n
653 else if (bgchild < 0)
(gdb)
672 }
(gdb)
BaseBackup () at pg_basebackup.c:1937
1937 for (i = 0; i < PQntuples(res); i++)
(gdb)pg_wal目录中的数据
[xdb@localhost backup]$ ls -l ./pg_wal/
total 16388
-rw-------. 1 xdb xdb 16777216 Mar 18 11:54 000000100000000000000057
-rw-------. 1 xdb xdb 217 Mar 18 11:54 00000010.history
drwx------. 2 xdb xdb 35 Mar 18 11:54 archive_status
[xdb@localhost backup]$到此，相信大家对“PostgreSQL中StartLogStreamer分析”有了更深的了解，不妨来实际操作一番吧！这里是亿速云网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！
