ZAB(zookeeper原子广播)

简要介绍Zookeeper的ZAB原理

注意:ZAB协议以主从服务高可用为目标对外提供一致性保证

Read-Write过程

ZAB

Leader的重新选举(ZAB不指定算法,使用方自己实现如FLE)

ZAB

新的Leader 启动后数据一致性保证方案

ZAB

在数据同步完成后,准Leader成为真正意义Leader

总之,ZAB注重一致性目标的灾后恢复,是zk的核心一致性协议

TCP 握手

介绍TCP握手调用场景

注意状态变更时机

查看当前连接状态

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netstat -anptl | grep your_service

抓包查看

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tcpdump -i eth0 -vv
#一般通过wireshark配合,毕竟Windows环境下页面查看与分析直观些

调用与返回关系简图

TCP握手流程图

Read与Write调用处理流程简图

介绍read-write系统调用场景

注意read,write在缓冲区有无数据的情况下处理方式【返回状态】

NAME

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read - read from a file descriptor
write - write to a file descriptor

SYNOPSIS

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#include <unistd.h>
ssize_t read(int fd, void *buf, size_t count);
ssize_t write(int fd, const void *buf, size_t count);

DESCRIPTION

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read ---
read() attempts to read up to count bytes from file descriptor fd into the buffer starting at buf.
If count is zero, read() returns zero and has no other results. If count is greater than SSIZE_MAX, the result is
unspecified.
write ---
write() writes up to count bytes from the buffer pointed buf to the file referred to by the file descriptor fd.
The number of bytes written may be less than count if, for example, there is insufficient space on the underlying phys-
ical medium, or the RLIMIT_FSIZE resource limit is encountered (see setrlimit(2)), or the call was interrupted by a
signal handler after having written less than count bytes. (See also pipe(7).)
For a seekable file (i.e., one to which lseek(2) may be applied, for example, a regular file) writing takes place at
the current file offset, and the file offset is incremented by the number of bytes actually written. If the file was
open(2)ed with O_APPEND, the file offset is first set to the end of the file before writing. The adjustment of the
file offset and the write operation are performed as an atomic step.
POSIX requires that a read(2) which can be proved to occur after a write() has returned returns the new data. Note
that not all file systems are POSIX conforming.

RETURN VALUE

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read ---
On success, the number of bytes read is returned (zero indicates end of file), and the file position is advanced by
this number. It is not an error if this number is smaller than the number of bytes requested; this may happen for
example because fewer bytes are actually available right now (maybe because we were close to end-of-file, or because we
are reading from a pipe, or from a terminal), or because read() was interrupted by a signal. On error, -1 is returned,
and errno is set appropriately. In this case it is left unspecified whether the file position (if any) changes.
write ---
On success, the number of bytes written is returned (zero indicates nothing was written). On error, -1 is returned,
and errno is set appropriately.
If count is zero and fd refers to a regular file, then write() may return a failure status if one of the errors below
is detected. If no errors are detected, 0 will be returned without causing any other effect. If count is zero and fd
refers to a file other than a regular file, the results are not specified.

调用与返回关系简图

Read-Write流程图