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Subject: Escaping a blocked sendto() syscall without causing a restart
To: pgsql-admin@postgresql.org 
From: Jerry Sievers <gsievers19@comcast.net>
Date: Thu, 17 Jan 2013 14:36:24 -0600
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Does anyone know if one of the signals below can be sent to break out
,of this state *without* the postmaster sensing a crashed backend?

I've seen several times in the past at other companies, backends that
will not respond to cancel nor SIGTERM due to syscall that's blocked
on IO.

Quite often though apparently the backend would notice the broken
socket eventually and receive the signals and exit cleanly.

I've got one that's been wedged like that for  a couple days now. 

I recall trying several  in a similar situation a while ago and of
course one of them  interrupted the syscall all right but it was an
abort and we got the customary spontaneous postmaster restart.


 PostgreSQL 8.4.13 on x86_64-pc-linux-gnu, compiled by GCC gcc-4.3.real (Debian 4.3.2-1.1) 4.3.2, 64-bit

$ uname -a
Linux somebox.foo.zizzy 2.6.36 #5 SMP Thu Jul 28 17:52:31 UTC 2011 x86_64 GNU/Linux
$ 
$ strace -p 31603
Process 31603 attached - interrupt to quit
sendto(9, "default_rate_3m_v4: 0.1224\nmonth_"..., 3440, 0, NULL, 0
 <unfinished ...>
Process 31603 detached
$ $ 
$ 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	
$ 

Thanks

-- 
Jerry Sievers
e: jerry.sievers@comcast.net
p: 312.241.7800


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