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

[Ashutosh B. <ash...@en...>]

A naive question,
Can we also cleanup the pending list?


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