[Postgres-xl-general] Getting "Failed to get pooled connections" when 1 datanode is down

Rick Mtek rickmtek at gmail.com
Tue Feb 10 09:35:59 PST 2015


On Tue, Feb 10, 2015 at 12:49 AM, Pavan Deolasee <pavan.deolasee at gmail.com>
wrote:

>
>
> On Tue, Feb 10, 2015 at 5:38 AM, Rick Mtek <rickmtek at gmail.com> wrote:
>
>> Hello,
>> As a proof of concept I configured:
>> - GTM - Machine A
>> - GTM Proxy - Machine B
>> - Coord1/datanode1 - Machine B
>> - GTM Proxy - Machine C
>> - Coord2/datanode2 - Machine C
>>
>> Created a distributed table, inserted some records. All seems to be
>> working fine and data is being distributed as expected. Then I shutdown
>> Machine C, so one datanode is gone.
>> As a result of that when I query the distributed table from the remaining
>> live node (machine A) I got the following message:
>>
>> my_poc_xl=# SELECT * FROM distributed_table;
>> ERROR:  Failed to get pooled connections
>> Time: 3000.144 ms
>>
>> 1) The above means that if by any chance one datanode is down or not
>> accessible the whole system/cluster data will be not accessible by the
>> application?
>>
>
>
> Since your query needs access to the failed datanode, you see the error.
> If you instead run a SELECT query with a WHERE clause such that it requires
> access to just the running node, it should work OK.
>
> Thanks,
> Pavan
>
>
Pavan, if I run the query against the other datanodes it works as you
mentioned. No doubts about it. That works fine, but the application does
not know anything about datanodes. For the application this is a just one
big database (behind scenes threre are several machines with GTM,
Coordinators and Datanodes).

Still these questions are unanswered:

1) if by any chance one datanode is down or not accessible the whole
system/cluster data will be not accessible by the UI application?
(ERROR:  Failed to get pooled connections)
2) How to keep getting results from all the others datanodes even if
one is not accessible from the UI? (querying manually each
datanode?????)
3) What should be the expected results when query a distributed table
having one datanode down? (An Error?)

Thanks.
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