Re: [Postgres-xc-developers] GTM/GTM Proxy invalid handles and failed to get snapshot issues

[Koichi S. <koi...@gm...>]

2013/8/6 Nikhil Sontakke <ni...@st...>

>
>
>
>> Can GTM/proxy cleanup the pending list when it detects the death of a
>> connection, just like GTM does its cleanup?
>>
>>
> Well, the pending requests are not stored in a per client list. We could
> go and look for this specific client in the list though and clean it up.
> But remember that the client might have given a set of instructions to the
> proxy and disappeared legitimately. So processing all requests in order
> before processing the disconnection seems much cleaner.
>

Yes, it makes sense.    BTW, all the pending and processed list for each
select() cycle is cleaned up.
---
Koichi Suzuki


>
> Regards,
> Nikhils
>
>
>>
>> On Tue, Aug 6, 2013 at 11:03 AM, Nikhil Sontakke <ni...@st...>wrote:
>>
>>>
>>> A naive question,
>>>> Can we also cleanup the pending list?
>>>>
>>>>
>>> Umm, the processed commands are put onto the thr_processed_commands list
>>> and freed up eventually. Is that what you were asking?
>>>
>>> Regards,
>>> Nikhils
>>>
>>>>
>>>>  On Tue, Aug 6, 2013 at 9:56 AM, Nikhil Sontakke <ni...@st...>wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> We have had a long standing issue with a GTM Proxy in the mix. It has
>>>>> been reported here:
>>>>>
>>>>>
>>>>> http://sourceforge.net/mailarchive/forum.php?thread_name=CAB7nPqQ51fabopxCOHPrRM%3D2WTJMikfZUPHNEW942DDHmED7bQ%40mail.gmail.com&forum_name=postgres-xc-developers
>>>>>
>>>>> I think I found the root cause:
>>>>>
>>>>> Here's how things work:
>>>>>
>>>>> The client connects to proxy. The proxy internally connects to the
>>>>> GTM.
>>>>>
>>>>> Some commands from clients are sent immediately to the GTM by the
>>>>> proxy.
>>>>>
>>>>> Some commands are put in the pending list on the proxy for batch
>>>>> processing later.
>>>>>
>>>>> Now, if the client goes away before processing pending commands, the
>>>>> proxy is immediately telling the GTM so. That initiates a cleanup on the
>>>>> GTM side and removes the XIDs associated with this client. After this
>>>>> cleanup when the GTM receives a command like "MSG_SNAPSHOT_GET" or
>>>>> "MSG_TXN_COMMIT_MULTI" etc. from the pending list from the proxy, then it's
>>>>> going to get confused.
>>>>>
>>>>> A way to handle this is to put "disconnected" messages also onto the
>>>>> pending list. We then process these "disconnected" messages LAST from the
>>>>> pending list.
>>>>>
>>>>> I have tried this fix and run a number of tests (using pgbench) and
>>>>> things seem to be ok. I do not see the invalid handle and snapshot errors
>>>>> on the GTM side with this patch in place.
>>>>>
>>>>> PFA, patches for 1.0, 1.1 and head attached with this email.
>>>>>
>>>>> Regards,
>>>>> Nikhils
>>>>> --
>>>>> StormDB - http://www.stormdb.com
>>>>> The Database Cloud
>>>>>
>>>>> ------------------------------------------------------------------------------
>>>>> Get your SQL database under version control now!
>>>>> Version control is standard for application code, but databases havent
>>>>> caught up. So what steps can you take to put your SQL databases under
>>>>> version control? Why should you start doing it? Read more to find out.
>>>>>
>>>>> http://pubads.g.doubleclick.net/gampad/clk?id=48897031&iu=/4140/ostg.clktrk
>>>>> _______________________________________________
>>>>> Postgres-xc-developers mailing list
>>>>> Pos...@li...
>>>>> https://lists.sourceforge.net/lists/listinfo/postgres-xc-developers
>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> Best Wishes,
>>>> Ashutosh Bapat
>>>> EntepriseDB Corporation
>>>> The Postgres Database Company
>>>>
>>>
>>>
>>>
>>> --
>>> StormDB - http://www.stormdb.com
>>> The Database Cloud
>>>
>>
>>
>>
>> --
>> Best Wishes,
>> Ashutosh Bapat
>> EntepriseDB Corporation
>> The Postgres Database Company
>>
>
>
>
> --
> StormDB - http://www.stormdb.com
> The Database Cloud
>
>
> ------------------------------------------------------------------------------
> Get your SQL database under version control now!
> Version control is standard for application code, but databases havent
> caught up. So what steps can you take to put your SQL databases under
> version control? Why should you start doing it? Read more to find out.
> http://pubads.g.doubleclick.net/gampad/clk?id=48897031&iu=/4140/ostg.clktrk
> _______________________________________________
> Postgres-xc-developers mailing list
> Pos...@li...
> https://lists.sourceforge.net/lists/listinfo/postgres-xc-developers
>
>