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

[Nikhil S. <ni...@st...>]

> 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
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>
>
> --
> Best Wishes,
> Ashutosh Bapat
> EntepriseDB Corporation
> The Postgres Database Company
>



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