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[vwnc] PostgreSQL Read request made while another request is active.

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Maarten Mostert-2

[vwnc] PostgreSQL Read request made while another request is active.

Hi,

When running my application on a remote PostgreSQL database ( a slicehost server), I often get the above mentioned message withe the enclosed stack trace

When running postgres locally it never shows up.

Anyone has the idea of how to solve this ?

Regards,

@+Maarten,

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Bruce Badger

Re: [vwnc] PostgreSQL Read request made while another request is active.

Taking the error message at it's word ...

Are there multiple Smalltalk processes using the same PostgreSQL connection?

Could some exception handling have caused an application level retry of a query?

Of course these are just wild guesses based on what the error message
seems to say.

2009/12/6 Maarten MOSTERT <[hidden email]>:

> Hi,
>
> When running my application on a remote PostgreSQL database ( a slicehost
> server), I often get the above mentioned message withe the enclosed stack
> trace
>
> When running postgres locally it never shows up.
>
> Anyone has the idea of how to solve this ?
>
> Regards,
>
> @+Maarten,
>
>
>
>
>
>
>
>
>
>
> _______________________________________________
> vwnc mailing list
> [hidden email]
> http://lists.cs.uiuc.edu/mailman/listinfo/vwnc
>
>

--
Make the most of your skills - with OpenSkills
http://www.openskills.org/
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Yanni Chiu

Re: [vwnc] PostgreSQL Read request made while another request is active.

In reply to this post by Maarten Mostert-2

Maarten MOSTERT wrote:
> When running my application on a remote PostgreSQL database ( a
> slicehost server), I often get the above mentioned message withe the
> enclosed stack trace
>
> When running postgres locally it never shows up.
>
> Anyone has the idea of how to solve this ?

When you test it locally, are you sure you're using real sockets? If
your connection configuration is using 'localhost' then you're probably
bypassing some network overhead. Since the request/response is so fast
on this loopback interface, you have less chance of reproducing your
timing problem.

Whether or not you can reproduce it locally, try increasing the debug
level on the postgres server. If you're lucky, you might spot the two
SQL stmts being made on the same connection, and then figure out how
these SQLs end up being issued on the same connection, at the same time.

If it turns out that your code is doing a re-try, maybe you can tweak
some socket parameters (on the server, on the client, in VW). Of course,
that would be a workaround, since the real problem looks like the
connection is not being shared properly between two queries.

Hope that helps.

--
Yanni

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Maarten Mostert-2

Re: [vwnc] PostgreSQL Read request made while another request isactive.

In reply to this post by Bruce Badger

Thanks Bruce and Yanni,

Yes I had a forked process doing some status bar updating. It is a bit
strange as it didn't really seem to bother me before, and it only happens
when I switch from one database to another. Taking the fork away solves the
problem for the moment however this really slows down the UI responses.

I never heard that you can't fork database acces ? and I don't quite
understand where a THAPI odbx interfaces stands for if this is the case ?

@+Maarten,

----- Original Message -----
From: "Bruce Badger" <[hidden email]>
To: "Glorp" <[hidden email]>; "VWNC" <[hidden email]>
Sent: Sunday, December 06, 2009 7:01 PM
Subject: Re: [vwnc] PostgreSQL Read request made while another request
isactive.

>
> Taking the error message at it's word ...
>
> Are there multiple Smalltalk processes using the same PostgreSQL
> connection?
>
> Could some exception handling have caused an application level retry of a
> query?
>
> Of course these are just wild guesses based on what the error message
> seems to say.
>
> 2009/12/6 Maarten MOSTERT <[hidden email]>:
>> Hi,
>>
>> When running my application on a remote PostgreSQL database ( a slicehost
>> server), I often get the above mentioned message withe the enclosed stack
>> trace
>>
>> When running postgres locally it never shows up.
>>
>> Anyone has the idea of how to solve this ?
>>
>> Regards,
>>
>> @+Maarten,
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> _______________________________________________
>> vwnc mailing list
>> [hidden email]
>> http://lists.cs.uiuc.edu/mailman/listinfo/vwnc
>>
>>
>
>
>
> --
> Make the most of your skills - with OpenSkills
> http://www.openskills.org/
> _______________________________________________
> vwnc mailing list
> [hidden email]
> http://lists.cs.uiuc.edu/mailman/listinfo/vwnc
>
>

_______________________________________________
vwnc mailing list
[hidden email]
http://lists.cs.uiuc.edu/mailman/listinfo/vwnc

Bruce Badger

Re: [vwnc] PostgreSQL Read request made while another request isactive.

You can run two connections to the same database if you like. This
will consume more resources at both ends, but it may be a reasonable
compromise in your case.

THAPI is a way of running code (e.g. a C library) in a native thread
in the same OS process as the VM (IIRC). The PostgreSQL drivers are
100% pure Smalltalk and so run in green threads in the VM.

I have thought about making the PostgreSQL drivers thread safe, but I
don't think it's a trivial problem and I have not come across a case
where I needed it, so I have not had a really good test case.

... so it's on my (rather long) list of things to do.

2009/12/7 Maarten MOSTERT <[hidden email]>:

> Thanks Bruce and Yanni,
>
> Yes I had a forked process doing some status bar updating. It is a bit
> strange as it didn't really seem to bother me before, and it only happens
> when I switch from one database to another. Taking the fork away solves the
> problem for the moment however this really slows down the UI responses.
>
> I never heard that you can't fork database acces ? and I don't quite
> understand where a THAPI odbx interfaces stands for if this is the case ?
>
> @+Maarten,
>
> ----- Original Message ----- From: "Bruce Badger" <[hidden email]>
> To: "Glorp" <[hidden email]>; "VWNC" <[hidden email]>
> Sent: Sunday, December 06, 2009 7:01 PM
> Subject: Re: [vwnc] PostgreSQL Read request made while another request
> isactive.
>
>
>>
>> Taking the error message at it's word ...
>>
>> Are there multiple Smalltalk processes using the same PostgreSQL
>> connection?
>>
>> Could some exception handling have caused an application level retry of a
>> query?
>>
>> Of course these are just wild guesses based on what the error message
>> seems to say.
>>
>> 2009/12/6 Maarten MOSTERT <[hidden email]>:
>>>
>>> Hi,
>>>
>>> When running my application on a remote PostgreSQL database ( a slicehost
>>> server), I often get the above mentioned message withe the enclosed stack
>>> trace
>>>
>>> When running postgres locally it never shows up.
>>>
>>> Anyone has the idea of how to solve this ?
>>>
>>> Regards,
>>>
>>> @+Maarten,
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> vwnc mailing list
>>> [hidden email]
>>> http://lists.cs.uiuc.edu/mailman/listinfo/vwnc
>>>
>>>
>>
>>
>>
>> --
>> Make the most of your skills - with OpenSkills
>> http://www.openskills.org/
>> _______________________________________________
>> vwnc mailing list
>> [hidden email]
>> http://lists.cs.uiuc.edu/mailman/listinfo/vwnc
>>
>>
>
>
>
>