[Pgpool-hackers] pgpool-II 3.0.4 release

[Tatsuo Ishii]

>> So it seems we need to wait for find_primary_node_repeatedly finish
>> before we issue pcp_attach_node. This suggests that your fix might not
>> be appropreate because your fix does not corresponds to this "timing"
>> issue.
>> 
>> I'm going to keep on looking into this...
> 
> That's actually not the issue I'm talking about. I'm in V3.0, with a
> single backend, no failover script. See my config in attachment.

Ok. pgpool-II-3.0-stable does not use find_primary_node_repeatedly()
and it does not have the problem I'm talking about.

> When I do the pcp_detach_node, I have this:
> 
> 2011-05-25 20:24:12 LOG:   pid 31861: notice_backend_error: 0 fail over
> request from pid 31861
> 2011-05-25 20:24:12 LOG:   pid 31828: starting degeneration. shutdown
> host localhost(5432)
> 2011-05-25 20:24:12 ERROR: pid 31828: failover_handler: no valid DB node
> found
> 2011-05-25 20:24:12 LOG:   pid 31828: failover done. shutdown host
> localhost(5432)
> 
> Which seems fine to me. Then I do the pcp_attach_node, and I got this:
> 
> 2011-05-25 20:25:23 LOG:   pid 31861: send_failback_request: fail back 0
> th node request from pid 31861
> 2011-05-25 20:25:23 ERROR: pid 31861: send_failback_request: node 0 is
> alive.
> 
> I was mistaken on the "node 0 is alive" message. I thought it means that
> node 0 is NOW up. What it really means is that pgpool thought it was
> ALREADY alive (hence the ERROR message level on the
> send_failback_request function). Digging harder on this issue, I finally
> found that the VALID_BACKEND macro returns true when it should return
> false. Actually, there is already this comment in get_next_master_node():
> 
>         /*
>          * Do not use VALID_BACKEND macro in raw mode.
>          * VALID_BACKEND return true only if the argument is master
>          * node id. In other words, standby nodes are false. So need
>          * to check backend status without VALID_BACKEND.
>          */
> 
> And I'm actually in raw mode. VALID_BACKEND is used so much it would be
> really dangerous to change it. So, I'm not sure what we really should do
> here. I've got a patch that fixes my issue cleanly, not sure it's the
> best way to do this. See the patch in attachment.

My suggestion is, leave this as it is for 3.0.4. I think we need more
time to investigate it. Let's continue the work after 3.0.4 released.
We already have critical issues such as "unnamed statement not found"
with 3.0.3, and I have personaly sent to users who were troubled by
this issue the 3.0-STABLE CVS tar ball by their request. If we delay
the 3.0.4 release, more and more this kind of questions/requests will
be coming. I don't want to be troubled...

> BTW, when I do a pcp_attach_node, I have the status 2, but it didn't
> check if there was a PostgreSQL backend available. Not sure we want to
> do something on this too. Why doesn't it check if the backend is
> available? it doesn't do at startup too. I find this really weird, but
> I'm sure there is a reason.

It's a design decision. pcp_attach_node is supposed to be used by
human(or smart management tool) and he/she should know what he/she is
doing. That says he/she should make sure if the backend actually
usable: just it is up and running is not enough. For example, in
replication mode, it must be synched with other backend before
pcp_attach_node is used.
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp