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#1 (**permalink**) 04-12-2008, 08:39 AM

I'm looking into PG/PLSql code and following code in
plpgsql_call_handler looks strange:

/* Find or compile the function */
func = plpgsql_compile(fcinfo, false);

/* Mark the function as busy, so it can't be deleted from under
us */
func->use_count++;

I don't have deep knowledge about this part of code. But what happen if
in parallel execution "func" will be deleted between these two lines?

Zdenek

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#2 (**permalink**) 04-12-2008, 08:39 AM

Zdenek Kotala <Zdenek.Kotala@Sun.COM> writes:
> I'm looking into PG/PLSql code and following code in
> plpgsql_call_handler looks strange:

> /* Find or compile the function */
> func = plpgsql_compile(fcinfo, false);

> /* Mark the function as busy, so it can't be deleted from under
> us */
> func->use_count++;

> I don't have deep knowledge about this part of code. But what happen if
> in parallel execution "func" will be deleted between these two lines?

This is not a race condition because the backend is single-threaded.

(Hint: what it actually means by "function" is "the plpgsql function
cache entry I just found or built".)

regards, tom lane

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#3 (**permalink**) 04-12-2008, 08:39 AM

Tom Lane wrote:
> Zdenek Kotala <Zdenek.Kotala@Sun.COM> writes:
>> I'm looking into PG/PLSql code and following code in
>> plpgsql_call_handler looks strange:
>
>> /* Find or compile the function */
>> func = plpgsql_compile(fcinfo, false);
>
>> /* Mark the function as busy, so it can't be deleted from under
>> us */
>> func->use_count++;
>
>
>> I don't have deep knowledge about this part of code. But what happen if
>> in parallel execution "func" will be deleted between these two lines?
>
> This is not a race condition because the backend is single-threaded.

I see. Each backend has own function cache and use_count is for handle
recursion usage. Are my assumption correct?

thanks Zdenek

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#4 (**permalink**) 04-12-2008, 08:39 AM

Zdenek Kotala <Zdenek.Kotala@Sun.COM> writes:
> Tom Lane wrote:
>> This is not a race condition because the backend is single-threaded.

> I see. Each backend has own function cache and use_count is for handle
> recursion usage. Are my assumption correct?

Right. Once a function cache entry is set up, it exists unchanged until
no longer in use, no matter what happens to the underlying pg_proc row.

regards, tom lane

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race condition in pgplsql call handler?