postgresql三种shutdown

　　PostgreSQL shutdown有三种模式：

• smart：PostgreSQL 9.5之前，默认是该值，它需要等待会话全部退出后才停止。这几乎是不可能的。oracle的normal模式，也就是默认。
• fast：停止所有会话，执行检查点。相当于oracle的shutdown immeidate;
• immediate：停止所有会话，不执行检查点，相当于oracle的shutdown abort;

　　因为pg的检查点是全量的，如果希望尽可能影响时间短，可以采用下列方式停止：

psql -c CHECKPOINT && pg_ctl stop -m fast

https://www.enterprisedb.com/blog/postgresql-shutdown

　　除了通过pg_ctl停止外，也可以通过kill -SIGN停止pg进程。信号清单以及含义参见https://www.valinv.com/dev/linux-linux-signals-list。

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kill -l  1) SIGHUP       2) SIGINT       3) SIGQUIT      4) SIGILL       5) SIGTRAP  6) SIGABRT      7) SIGBUS       8) SIGFPE       9) SIGKILL     10) SIGUSR1 11) SIGSEGV     12) SIGUSR2     13) SIGPIPE     14) SIGALRM     15) SIGTERM 16) SIGSTKFLT   17) SIGCHLD     18) SIGCONT     19) SIGSTOP     20) SIGTSTP 21) SIGTTIN     22) SIGTTOU     23) SIGURG      24) SIGXCPU     25) SIGXFSZ 26) SIGVTALRM   27) SIGPROF     28) SIGWINCH    29) SIGIO       30) SIGPWR 31) SIGSYS      34) SIGRTMIN    35) SIGRTMIN+1  36) SIGRTMIN+2  37) SIGRTMIN+3 38) SIGRTMIN+4  39) SIGRTMIN+5  40) SIGRTMIN+6  41) SIGRTMIN+7  42) SIGRTMIN+8 43) SIGRTMIN+9  44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13 48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12 53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9  56) SIGRTMAX-8  57) SIGRTMAX-7 58) SIGRTMAX-6  59) SIGRTMAX-5  60) SIGRTMAX-4  61) SIGRTMAX-3  62) SIGRTMAX-2 63) SIGRTMAX-1  64) SIGRTMAX

执行kill -SIGxxx即可，不需要包含SIG三个字母。每个信号量的含义如下：

Action

Action	Description
Term	Terminate the process
Core	Terminate the process and dump core
Ign	Ignore the signal (cause a process toterminate and produce a core dump file, a disk file (named core of the current working directory of the process. On Linux, the name is configured through /proc/sys/kernel/core_pattern) containing animage of the process's memory at the time of termination.)
Stop	Stop the process
Cont	Continue the process if it is currently stopped

Standard Signals

Name	Value	Default Action	Description
SIGHUP	1	Term	Hangup detected on controlling terminalor death of controlling process.
SIGINT	2	Term	Interrupt from keyboard (often DELETE or Control-C)
SIGQUIT	3	Term + Core	Quit from keyboard (often Control-backslash)
SIGILL	4	Term + Core	Illegal Instruction
SIGTRAP	5	Term + Core	Trace/breakpoint trap
SIGABRT	6	Term + Core	Abort signal from abort (calling the abort function)
SIGBUS	10,7,10	Term + Core	Bus error (bad memory access)
SIGFPE	8	Term + Core	Arithmetic exception (such as divide by 0, floating-point overflow, and so on)
SIGKILL	9	Term	Kill signal (It provides the system administrator with a sure way to kill any process)
SIGUSR1	30,10,16	Term	User-defined signal 1, for use in application programs
SIGSEGV	11	Term + Core	Invalid memory reference (stands for "segmentation violation")
SIGUSR2	31,12,17	Term	User-defined signal 2, for use in application programs
SIGPIPE	13	Term	Broken pipe: write to pipe with noreaders (If we write to a pipeline but the reader has terminated, SIGPIPE is generated)
SIGALRM	14	Term	Timer signal from alarm (calling the alarm function)
SIGTERM	15	Term	Termination signal (Using SIGTERM gives programs a chance to terminate gracefully by cleaning up before exiting (in contrast to SIGKILL, which can't be caught or ignored))
SIGSTKFLT	-,16,-	Term	Stack fault on coprocessor (unused)
SIGCHLD	20,17,18	Ign	Child stopped or terminated (Whenever a process terminates or stops, the SIGCHLD signal is sent to the parent. By default, this signal is ignored, so the parent must catch this signal if it wants to be notified whenever a child's status changes. The normal action in the signal-catching function is to call one of the wait functions to fetch the child's process ID and termination status)
SIGCONT	19,18,25	Cont / Ign	Continue if a process stopped
SIGSTOP	17,19,23	Stop	Stop process
SIGTSTP	18,20,24	Stop	Stop typed at terminal (often Control-Z)
SIGTTIN	21,21,26	Stop	Terminal input for background process (generated when a process in a background process group tries to read from its controlling terminal)
SIGTTOU	22,22,27	Stop	Terminal output for background process (generated when a process in a background process group tries to write to its controlling terminal)
SIGURG	16,23,21	Ign	Urgent condition on socket (generated when out-of-band data is received on a network connection)
SIGXCPU	24,24,30	Term / (Term + Core)	CPU time limit exceeded (generated when a process exceeds its soft CPU time limit)
SIGXFSZ	25,25,31	Term / (Term + Core)	File size limit exceeded (generated when a process exceeds its soft file size limit)
SIGVTALRM	26,26,28	Term	Virtual alarm clock (generated when a virtual interval timer set by the setitimer(2) function expires)
SIGPROF	27,27,29	Term	Profiling timer expired (generated when a profiling interval timer set by the setitimer(2) function expires)
SIGWINCH	28,28,20	Ign	Window resize signal (The kernel maintains the size of the window associated with each terminal and pseudo terminal. A process can get and set the window size with the ioctl function. If a process changes the window size from its previous value using the ioctl set-window-size command, the kernel generates the SIGWINCH signal for the foreground process group)
SIGIO	23,29,22	Term / Ign	I/O now possible (Indicates an asynchronous I/O event)
SIGPWR	29,30,19	Term / Ign	Power fail/restart (Its main use is on a system that has an uninterruptible power supply (UPS))
SIGSYS	12,31,12	Term + Core	Bad argument to routine (Invalid system call. This might happen if you build a program that uses a new system call and you then try to run the same binary on an older version of the operating system where the system call doesn't exist)

Note: The signals SIGKILL and SIGSTOP cannot be caught, blocked, orignored.

https://www.postgresql.org/docs/14/server-shutdown.html