[Pgpool-hackers] retry of health check

[Tatsuo Ishii]

> Hi,
> 
> The health_check() in main.c retries to execute the health check from
> the beginning only when the message other than the ErrorResponse
> arrives from the backend and it fails in sending the Terminate message
> to the backend. Why do we need to retry that only in that case?
> The retry with template1 seems useless. Am I missing something?

It turns out that current behavior seems to be correct, not perfect
thought.

While writing the patch, I thought that after sending startup packet
with wrong user and/or datbase, backend returns E, rather than R. Here
is a strace of psql with wrong database name:

connect(3, {sa_family=AF_FILE, path="/tmp/.s.PGSQL.5433"}, 110) = 0
getsockopt(3, SOL_SOCKET, SO_ERROR, [0], [4]) = 0
getsockname(3, {sa_family=AF_FILE, path=@}, [2]) = 0
poll([{fd=3, events=POLLOUT|POLLERR, revents=POLLOUT}], 1, -1) = 1
rt_sigaction(SIGPIPE, {SIG_IGN}, {SIG_DFL}, 8) = 0
send(3, "\0\0\0#\0\3\0\0user\0t-ishii\0database\0uu"..., 35, 0) = 35
rt_sigaction(SIGPIPE, {SIG_DFL}, {SIG_IGN}, 8) = 0
poll([{fd=3, events=POLLIN|POLLERR, revents=POLLIN|POLLHUP}], 1, -1) = 1
recv(3, "R\0\0\0\10\0\0\0\0E\0\0\0QSFATAL\0C3D000\0Mdat"..., 16384, 0) = 91

As you can see, backend returns "R" follwing "E". Reading from docs, I
expected backend immediately returns "E" without "R". I'm not sure
this follows the frontend/backend protocol but we have to live with
it.

Anyway, backend then takes the liberty to discconnect the session
after sending above packet and pgpool sees write(2) error. Thus retry
to use "template1" database is correct in this case.
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp