[pgpool-general: 990] Re: using prepared statements when memory_cache_enabled=on

[Tatsuo Ishii]

I think no one can debug pgpool when it behaves completely sane.
Again, developers need reproducible test case. What you can do is, try
to find the case.
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp

> Yes, I understand that, but that's not a valid excuse for ignoring us.
>  I asked how we can debug this, and received no reply.  It looks like
> pgpool is doing something wrong.  How can I debug what its doing?
> 
> On Wed, Sep 12, 2012 at 2:36 PM, Tatsuo Ishii <ishii at postgresql.org> wrote:
>> I guess she stucks because she doesn't know how to reproduce the problem.
>> --
>> Tatsuo Ishii
>> SRA OSS, Inc. Japan
>> English: http://www.sraoss.co.jp/index_en.php
>> Japanese: http://www.sraoss.co.jp
>>
>>> The lack of response isn't comforting.  There's clearly a bug
>>> somewhere, and the only way it reproduces is when using pgpool with
>>> memcache enabled.  Does no one on the pgpool team care about this
>>> problem?
>>>
>>> On Mon, Sep 10, 2012 at 7:33 AM, Lonni J Friedman <netllama at gmail.com> wrote:
>>>> Nozomi, we'd appreciate some input & assistance.  thanks!
>>>>
>>>> On Thu, Sep 6, 2012 at 10:12 AM, Greg Swallow <gswallow at exacttarget.com> wrote:
>>>>> Yep.
>>>>>
>>>>> On Sep 6, 2012, at 1:10 PM, Lonni J Friedman wrote:
>>>>>
>>>>>> Its somewhat encouraging knowing its not just me.  Are you seeing the
>>>>>> same error that I'm seeing?
>>>>>>
>>>>>>
>>>>>> On Thu, Sep 6, 2012 at 6:53 AM, Greg Swallow <gswallow at exacttarget.com> wrote:
>>>>>>> I'm in the same boat, with a Rails app.  I can't reproduce it running the same query in psql, but once I turned the memory cache off, I stopped having this issue. I'm using membase and moxi, rather than memcached.  It's wire-format compatible from what I can tell.  PostgreSQL 9.1.4.  I can possibly help debug.
>>>>>>>
>>>>>>> On Sep 5, 2012, at 5:26 PM, Lonni J Friedman wrote:
>>>>>>>
>>>>>>>> On Tue, Sep 4, 2012 at 9:30 PM, Nozomi Anzai <anzai at sraoss.co.jp> wrote:
>>>>>>>>> Hi,
>>>>>>>>>
>>>>>>>>>> Greetings,
>>>>>>>>>> I'm running 3.2.0 with memory_cache_enabled=on and memqcache_method =
>>>>>>>>>> 'memcached', and I'm seeing really bizarre errors when using prepared
>>>>>>>>>> statements.  Basically any query that should use the prepared
>>>>>>>>>> statement is failing with:
>>>>>>>>>> server sent data ("D" message) without prior row description ("T" message)
>>>>>>>>>>
>>>>>>>>>> This only happens once the data has been cached by pgpool (with the
>>>>>>>>>> memcache server).  If I set memory_cache_enabled=off, then it works
>>>>>>>>>> fine.  I'm guessing that maybe the problem is that the prepared
>>>>>>>>>> statement isn't getting cached, so the queries which depend on the
>>>>>>>>>> prepared statement fail?
>>>>>>>>>>
>>>>>>>>>> Is this expected behavior?  If so, is there a work around that doesn't
>>>>>>>>>> require me to not cache the tables that the prepared statement
>>>>>>>>>> reference?
>>>>>>>>>
>>>>>>>>> I couldn't reproduce it by the following ways:
>>>>>>>>>
>>>>>>>>> 1) the attached simple Java program: pgsql.java (only executing one SELECT)
>>>>>>>>> 2) pgbench -M extended -f bench.sql
>>>>>>>>>
>>>>>>>>> Which version is your PostgreSQL? I tested with pgpool-II 3.2.0
>>>>>>>>> (officially released), PostgreSQL 9.1.0, and memcached 1.4.7.
>>>>>>>>
>>>>>>>> postgresql-9.1.5
>>>>>>>> memcached-1.4.10
>>>>>>>>
>>>>>>>> However, it looks like I was mistaken when I stated that this was
>>>>>>>> triggered with prepared statements.  I tried to put together a trivial
>>>>>>>> test case (similar to what you created), and now I can't replicate it.
>>>>>>>> So whatever is going wrong only seems to happen inside of my huge,
>>>>>>>> complex web app.    FWIW, I'm using PHP, not java.  All I know is that
>>>>>>>> this reproduces 100% of the time whenever memory_cache_enabled=on, and
>>>>>>>> never whenever memory_cache_enabled=off.
>>>>>>>>
>>>>>>>> I'm not sure how to debug this further.  Do you have any suggestions
>>>>>>>> on anything that I can change with pgpool to better isolate what's
>>>>>>>> going wrong?
>>>>>>