Re: Passing current_database to BackgroundWorkerInitializeConnection

[Andres Freund]

Hi,

On 2018-04-02 14:33:54 -0500, Jeremy Finzel wrote:
> Hmmm... not sure if I follow.  My goal is to run a SQL statement every 10
> seconds (or what value is chosen) in a particular database, using a
> background worker.  Those are the two arguments.  Am I missing some way to
> implement this apart from passing those 2 arguments into the launcher
> function?  Is the way to do this properly then to allocate shared memory
> for it, as opposed to trying to pass args into the main function?

Yes, that's the proper way. Allocate shared memory and pass a pointer to
that as the argument.

Greetings,

Andres Freund

Re: Passing current_database to BackgroundWorkerInitializeConnection

[Jeremy Finzel]

On Mon, Apr 2, 2018 at 2:27 PM, Andres Freund  wrote:

> Hi,
>
> On 2018-04-02 14:24:53 -0500, Jeremy Finzel wrote:
> > Thank you, this makes sense.  However, how can this be done since I can
> > only pass one argument to bgw_main?  Is there any way to do this without
> > having to store the value in shared memory?
>
> No (I mean you can store it in the filesystem or such as well, but
> ...). Pretty fundamentally sharing data between concurrently running
> processes needs a medium to share the data over. The bgw infrastructure
> allocates just enough so you can put an index to it into
> shmem. Allocating more would be wasteful and/or not enough for some
> users.
>
> Greetings,
>
> Andres Freund
>

Hmmm... not sure if I follow.  My goal is to run a SQL statement every 10
seconds (or what value is chosen) in a particular database, using a
background worker.  Those are the two arguments.  Am I missing some way to
implement this apart from passing those 2 arguments into the launcher
function?  Is the way to do this properly then to allocate shared memory
for it, as opposed to trying to pass args into the main function?

Thanks,
Jeremy

Re: Passing current_database to BackgroundWorkerInitializeConnection

[Andres Freund]

Hi,

On 2018-04-02 14:24:53 -0500, Jeremy Finzel wrote:
> Thank you, this makes sense.  However, how can this be done since I can
> only pass one argument to bgw_main?  Is there any way to do this without
> having to store the value in shared memory?

No (I mean you can store it in the filesystem or such as well, but
...). Pretty fundamentally sharing data between concurrently running
processes needs a medium to share the data over. The bgw infrastructure
allocates just enough so you can put an index to it into
shmem. Allocating more would be wasteful and/or not enough for some
users.

Greetings,

Andres Freund

Re: Passing current_database to BackgroundWorkerInitializeConnection

[Jeremy Finzel]

On Fri, Mar 30, 2018 at 5:37 PM, Andres Freund  wrote:

>
>
> On March 30, 2018 3:16:31 PM PDT, Jeremy Finzel  wrote:
> >> What do you mean with "current database"? Before you
> >> BackgroundWorkerInitializeConnection() there is no such thing?
> >
> >
> >My module is based directly off the worker_spi example. The worker is
> >dynamically launched via SQL command. But in the worker_spi example,
> >the
> >database postgres is just hardcoded as the database in which to start
> >the
> >background worker process. Instead, I want to start it in the database
> >in
> >which I run the SQL command.
>
> The started worker isn't associated with the original database. You can
> pass the database oid as an argument to the launched bgworker.
>
>
Thank you, this makes sense.  However, how can this be done since I can
only pass one argument to bgw_main?  Is there any way to do this without
having to store the value in shared memory?  I was going to try passing an
array instead of an int, but I'm not liking that much.  I am trying to pass
naptime and database_name (or oid).

Thanks,
Jeremy

Re: Passing current_database to BackgroundWorkerInitializeConnection

[Andres Freund]

On March 30, 2018 3:16:31 PM PDT, Jeremy Finzel  wrote:
>> What do you mean with "current database"? Before you
>> BackgroundWorkerInitializeConnection() there is no such thing?
>
>
>My module is based directly off the worker_spi example. The worker is
>dynamically launched via SQL command. But in the worker_spi example,
>the
>database postgres is just hardcoded as the database in which to start
>the
>background worker process. Instead, I want to start it in the database
>in
>which I run the SQL command.

The started worker isn't associated with the original database. You can pass 
the database oid as an argument to the launched bgworker.

Andres

-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.

Re: Passing current_database to BackgroundWorkerInitializeConnection

[Jeremy Finzel]

> What do you mean with "current database"? Before you
> BackgroundWorkerInitializeConnection() there is no such thing?


My module is based directly off the worker_spi example. The worker is
dynamically launched via SQL command. But in the worker_spi example, the
database postgres is just hardcoded as the database in which to start the
background worker process. Instead, I want to start it in the database in
which I run the SQL command.

Thank you!

Jeremy

>

Re: Passing current_database to BackgroundWorkerInitializeConnection

[Andres Freund]

On 2018-03-30 16:36:59 -0500, Jeremy Finzel wrote:
> I am having trouble figuring out the right way to do this, clearly missing
> something obvious.  I am simply trying to pass the current database
> to BackgroundWorkerInitializeConnection, but MyDatabaseId is showing as 0,
> and I am getting this error in the running of function get_database_name
> here at the top:

What do you mean with "current database"? Before you
BackgroundWorkerInitializeConnection() there is no such thing?

Greetings,

Andres Freund

Passing current_database to BackgroundWorkerInitializeConnection

[Jeremy Finzel]

I am having trouble figuring out the right way to do this, clearly missing
something obvious.  I am simply trying to pass the current database
to BackgroundWorkerInitializeConnection, but MyDatabaseId is showing as 0,
and I am getting this error in the running of function get_database_name
here at the top:

ERROR:  invalid cache ID: 21

char   *database_name = get_database_name(MyDatabaseId);

/*
...
*/

/* Connect to our database */
BackgroundWorkerInitializeConnection(database_name, NULL);


Any direction would be much appreciated.  I have tried to look at example
uses of MyDatabaseId and not sure what I'm missing here.

Thanks,
Jeremy