Обсуждение: creating and accessing temp table data inside a non-committed transaction

Plpgsql experts:

I've got a situation and am wondering if temp tables are the accepted solution.  (setting the temp
parameter on create table)  I've never worked with them and a colleague just brought them to my
attention as a way to solve a problem I've encountered.  He's not sure about this, so I am hoping
you guys can point me in the right direction.

The problem is that I've got function that takes some parameters, for example:

set constraints all deferred;
select my_func( x, y, z );
commit;

The problem is that the values x, y and z are inserted into a permanent table Q early in the processing of
my_func.  Then, several calls down in deep_func(), still inside my_func, I need to access the value of x.  I
tried to do a select on Q to get the value, but I came up NULL!  Guessing that is because the transaction
hasn't committed yet since I am still inside my_func.  Right?

So how do I get the value of parameter x?  Possible solutions:

    1) just pass x all the way down the calling path so that deep_func( x )  can just access it as a
        parameter value.  Pain in the butt because none of the intermediate calls need x.

    2) insert the value of a into a temp table and the do a select on that within deep_func().
        But will I stull come up NULL, or do temp tables work differently?

    3) some other technique if I am thinking about this totally the wrong way!

As always, help clearing my confusion muchly appreciated!  (obviously I can just do a bunch of experiments on my
own, but expert insight is always nice to have)

- Leon

Leon Starr <leon_starr@modelint.com> wrote:

> The problem is that the values x, y and z are inserted into a
> permanent table Q early in the processing of my_func.  Then,
> several calls down in deep_func(), still inside my_func, I need to
> access the value of x.  I tried to do a select on Q to get the
> value, but I came up NULL! Guessing that is because the
> transaction hasn't committed yet since I am still inside my_func.
> Right?

I don't think so.  Any database changes made by a transaction should
be visible to that transaction.  When you say "several calls down in
deep_func()", you don't mean that you are in a BEFORE trigger
function, or a function called from a BEFORE trigger, do you?

Perhaps you could boil the issue down to a small self-contained
example of the issue?

-Kevin

Ah!  That's what I had originally thought.  So, if what you are saying is true,
then I just have a bug of some sort.  I am NOT using any triggers.  It's just a
simple function with deeper function calls nested about 5 levels down.

To slightly rephrase:  Any database changes (inserts/updates) made by a transaction are visible
inside that transaction.  So if I do an insert inside a transaction and then later, within the same
transaction, do a select on the inserted row, I should select the data that I inserted.  Correct?

I will do my diagnostics with that in mind.  Thanks!

- Leon


On Jan 31, 2011, at 7:42 AM, Kevin Grittner wrote:

> Leon Starr <leon_starr@modelint.com> wrote:
>
>> The problem is that the values x, y and z are inserted into a
>> permanent table Q early in the processing of my_func.  Then,
>> several calls down in deep_func(), still inside my_func, I need to
>> access the value of x.  I tried to do a select on Q to get the
>> value, but I came up NULL! Guessing that is because the
>> transaction hasn't committed yet since I am still inside my_func.
>> Right?
>
> I don't think so.  Any database changes made by a transaction should
> be visible to that transaction.  When you say "several calls down in
> deep_func()", you don't mean that you are in a BEFORE trigger
> function, or a function called from a BEFORE trigger, do you?
>
> Perhaps you could boil the issue down to a small self-contained
> example of the issue?
>
> -Kevin

Oops.  Just noticed that I accidentally posted to the wrong group.  I meant to put this in Novice!
But thanks anyway!

- Leon

On Jan 31, 2011, at 7:42 AM, Kevin Grittner wrote:

> Leon Starr <leon_starr@modelint.com> wrote:
>
>> The problem is that the values x, y and z are inserted into a
>> permanent table Q early in the processing of my_func.  Then,
>> several calls down in deep_func(), still inside my_func, I need to
>> access the value of x.  I tried to do a select on Q to get the
>> value, but I came up NULL! Guessing that is because the
>> transaction hasn't committed yet since I am still inside my_func.
>> Right?
>
> I don't think so.  Any database changes made by a transaction should
> be visible to that transaction.  When you say "several calls down in
> deep_func()", you don't mean that you are in a BEFORE trigger
> function, or a function called from a BEFORE trigger, do you?
>
> Perhaps you could boil the issue down to a small self-contained
> example of the issue?
>
> -Kevin