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Date: Fri, 17 Feb 2023 17:43:13 +0900
From: Katsuragi Yuta <katsuragiy@oss.nttdata.com>
To: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>
Cc: 'Ted Yu' <yuzhihong@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, vignesh C
 <vignesh21@gmail.com>, pgsql-hackers@lists.postgresql.org,
 =?UTF-8?Q?=C3=96nder_Kalac=C4=B1?= <onderkalaci@gmail.com>, Fujii Masao
 <masao.fujii@oss.nttdata.com>, Shinya11.Kato@oss.nttdata.com, Kyotaro
 Horiguchi <horikyota.ntt@gmail.com>
Subject: Re: [Proposal] Add foreign-server health checks infrastructure
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On 2023-02-09 23:39, Hayato Kuroda (Fujitsu) wrote:
> Dear Katsuragi-san,
> 
> Thank you for reviewing! PSA new version patches.

Thank you for updating the patch! These are my comments,
please check.

0001:
Extending pqSocketPoll seems to be a better way because we can
avoid having multiple similar functions. I also would like to hear
horiguchi-san's opinion whether this matches his expectation.
Improvements of pqSocketPoll/pqSocketCheck is discussed in this
thread[1]. I'm concerned with the discussion.

As for the function's name, what do you think about keeping
current name (pqSocketCheck)? pqSocketIsReadable... describes
the functionality very well though.

pqConnCheck seems to be a family of pqReadReady or pqWriteRedy,
so how about placing pqConnCheck below them?

+ * Moreover, when neither forRead nor forWrite is requested and timeout 
is
+ * disabled, try to check the health of socket.
Isn't it better to put the comment on how the arguments are
interpreted before the description of return value?

+#if defined(POLLRDHUP)
+			input_fd.events = POLLRDHUP | POLLHUP | POLLNVAL;
...
+	input_fd.events |= POLLERR;
To my understanding, POLLHUP, POLLNVAL and POLLERR are ignored
in event. Are they necessary?


0002:
As for the return value of postgres_fdw_verify_connection_states,
what do you think about returning NULL when connection-checking
is not performed? I think there are two cases 1) ConnectionHash
is not initialized or 2) connection is not found for specified
server name, That is, no entry passes the first if statement below
(case 2)).

```
          if (all || entry->serverid == serverid)
          {
              if (PQconnCheck(entry->conn))
              {
```

0004:
I'm wondering if we should add kqueue support in this version,
because adding kqueue support introduces additional things to
be considered. What do you think about focusing on the main
functionality using poll in this patch and going for kqueue
support after this patch?


[1]: 
https://www.postgresql.org/message-id/20230209.115009.2229702014236187289.horikyota.ntt%40gmail.com

regards,

-- 
Katsuragi Yuta
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION