"Mendola Gaetano" <mendola@bigfoot.com> writes:
> I'm improving the Dllist in these direction:

AFAIR, catcache.c is the *only* remaining backend customer for Dllist,
and so any improvement for Dllist that breaks catcache is hardly an
improvement, no?

> 1) Avoid "if" statements in insertion/remove phase, for instance now the
> AddHeader appear like this:

<shrug> ... unless you can convert DLAddHead into a inline macro,
I doubt there'll be any visible performance difference.

> 2) Not using a malloc but using a "special" malloc that not perform
>    a malloc for each request but do a BIG malloc at first request...

It would make more sense to migrate Dllist to use palloc.  That's not
compatible with its use in frontend libpq; I've been speculating about
splitting off libpq to have a separate implementation instead of trying
to share code.  I believe libpq only uses Dllist for the
pending-notify-events list, for which the code is poorly optimized
anyway (we don't need a doubly-linked list for that).

			regards, tom lane

Mon, 30 Jun 2003 20:44:59 -0400
Tom Lane <tgl@sss.pgh.pa.us>
Re: Dllist public/private part 
I'm improving the Dllist in these direction:

1) Avoid "if" statements in insertion/remove phase, for instance now the
AddHeader appear like this:

void
DLAddHead(Dllist *l, Dlelem *e)
{
   Dlelem *where = l->dll_master_node->dle_next;
   e->dle_next = where;
   e->dle_prev = where->dle_prev;

   where->dle_prev->dle_next = e;
   where->dle_prev = e;

   e->dle_list = l;

}

2) Not using a malloc but using a "special" malloc that not perform
   a malloc for each request but do a BIG malloc at first request...



In the file dllist.h is not clear what is the public part and the private
part
of the implementation in particulary I see that somewhere in the code
there is the assumption that an Empty dllist is "zeroed"  instead of
use DLInitList, for example this is the way to initialize a struct that
contain a Dllist itself:

cp = (CatCache *) palloc0(sizeof(CatCache) + NCCBUCKETS * sizeof(Dllist));


this break my optimization because in my implementation a
dllist is

typedef struct Dllist
{
        Dlelem     *dll_master_node;
} Dllist;

and not anymore:

typedef struct Dllist
{
        Dlelem     *dll_head;
        Dlelem     *dll_tail;
} Dllist;

and is empty if list->dll_master_node->dle_next and
list->master_node->dle_prev are pointing to
list->master_node ( previously allocated in DLInitList).

What should I do ?  Forget the point 1)  ?


Regards
Gaetano Mendola



Tue, 1 Jul 2003 05:25:06 +0200
"Mendola Gaetano" <mendola@bigfoot.com>
Dllist public/private part
"Tom Lane" <tgl@sss.pgh.pa.us> wrote:
> "Mendola Gaetano" <mendola@bigfoot.com> writes:
> > I'm improving the Dllist in these direction:
>
> AFAIR, catcache.c is the *only* remaining backend customer for Dllist,
> and so any improvement for Dllist that breaks catcache is hardly an
> improvement, no?
>
> > 1) Avoid "if" statements in insertion/remove phase, for instance now the
> > AddHeader appear like this:
>
> <shrug> ... unless you can convert DLAddHead into a inline macro,
> I doubt there'll be any visible performance difference.
> > 2) Not using a malloc but using a "special" malloc that not perform
> >    a malloc for each request but do a BIG malloc at first request...
>
> It would make more sense to migrate Dllist to use palloc.  That's not
> compatible with its use in frontend libpq; I've been speculating about
> splitting off libpq to have a separate implementation instead of trying
> to share code.  I believe libpq only uses Dllist for the
> pending-notify-events list, for which the code is poorly optimized
> anyway (we don't need a doubly-linked list for that).

This mean that is waste of time work on dllist.
I seen that exist a TODO list about "features",
exist a list about: "code to optimize" ?


Regards
Gaetano Mendola



Tue, 1 Jul 2003 14:09:22 +0200
"Mendola Gaetano" <mendola@bigfoot.com>
Re: Dllist public/private part 
Mendola Gaetano wrote:
> "Tom Lane" <tgl@sss.pgh.pa.us> wrote:
> > "Mendola Gaetano" <mendola@bigfoot.com> writes:
> > > I'm improving the Dllist in these direction:
> >
> > AFAIR, catcache.c is the *only* remaining backend customer for Dllist,
> > and so any improvement for Dllist that breaks catcache is hardly an
> > improvement, no?
> >
> > > 1) Avoid "if" statements in insertion/remove phase, for instance now the
> > > AddHeader appear like this:
> >
> > <shrug> ... unless you can convert DLAddHead into a inline macro,
> > I doubt there'll be any visible performance difference.
> > > 2) Not using a malloc but using a "special" malloc that not perform
> > >    a malloc for each request but do a BIG malloc at first request...
> >
> > It would make more sense to migrate Dllist to use palloc.  That's not
> > compatible with its use in frontend libpq; I've been speculating about
> > splitting off libpq to have a separate implementation instead of trying
> > to share code.  I believe libpq only uses Dllist for the
> > pending-notify-events list, for which the code is poorly optimized
> > anyway (we don't need a doubly-linked list for that).

I certainly would like to see Dllist removed too.

> This mean that is waste of time work on dllist.
> I seen that exist a TODO list about "features",
> exist a list about: "code to optimize" ?

What TODO item where you looking at? 

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

Tue, 1 Jul 2003 15:03:51 -0400 (EDT)
Bruce Momjian <pgman@candle.pha.pa.us>
Re: Dllist public/private part
"Bruce Momjian" <pgman@candle.pha.pa.us> wrote:
> Mendola Gaetano wrote:
> I certainly would like to see Dllist removed too.
> 
> > This mean that is waste of time work on dllist.
> > I seen that exist a TODO list about "features",
> > exist a list about: "code to optimize" ?
> 
> What TODO item where you looking at? 

I see the http://developer.postgresql.org/todo.php
and for someone that want start to code is really 
hard reading for example:

. Cache last known per-tuple offsets to speed long tuple access 

what can do a "postgres source beginner" after reading that
sentence ?
May be is more usefull if a very "postgres source" expert, like
Bruce Momjian or Tom Lane, will compile a more detailed list
about what to do like: 
    We need a really efficient double linked list with this 
    interface blah blah blah or something like that

I hope I was clear enough

Regards
Gaetano Mendola 



    


Wed, 2 Jul 2003 09:27:13 +0200
"Mendola Gaetano" <mendola@bigfoot.com>
Re: Dllist public/private part