[Bizgres-general] [ENG] Re: Statement Queuing take II - Resource Scheduling

[Mark Kirkwood]

Alon Goldshuv wrote:
>
> Keep in mind that:
>
> - in between FETCHes other non related cursor commands may be executed.
> - there can be many cursors running, just waiting to be retrieved from
> shared memory when it's their turn to FETCH, and then wait for the next one.
> I guess this will mean 1 lock for every live cursor.
> - cursor doesn't always get closed by a CLOSE command. If the transaction is
> finished the cursor is closed automatically. So maybe PortalDrop is a
> strategic place to look at (?)
>
>   
I found 2 bugs connected with cursors and prepared statements last week.

The first was that I had not handled unnamed prepared statements in 
exec_parse_message, so was trivial to fix.

The second relates to having more than one cursor open at the same time 
- the code is garbage collecting the PROCLOCK entry when the first 
cursor closes, and so I get a missing PROCLOCK when the second one tries 
to close (don't know how I missed this till now... but anyway).

What I need to do (I think), is to alter the lock granularity from queue 
level to queue and statement level. This makes code still work pretty 
much like standard locks and turns out to have some nice benefits for 
the more sophisticated limit types (COST etc) e.g:

We need to remember the increment that we are requesting (e.g. a 
statement's cost) - for lock acquisition *and* release. This is most 
sensibly done by amending the PROCLOCK structure to accommodate an array 
of increments. Now if we have 1 lock per queue, this array needs to be 
variable sized (1 set of increments for each statement that 1 process 
has running or waiting). However if I have 1 lock per queue and 
statement, then we only need 1 set of increments  (i.e. fixed size) for 
each process and statement. This seems much better!

Clearly to implement this I need a statement or portal id I can use - It 
seems that portals are referenced by name , which I can't use in a 
LOCKTAG, so before I go and add some simple integer counter similar to 
the unnamed_portal_count in CreateNewPortal, does anyone know of an 
existing one I can use?

Cheers

Mark