Internal memory fragmentation

In previous post I've advertised my text about trie representations.

Depending on particular representation internal memory fragmentation vary from 25% to 46% (in GNU libc). In other words if trie should occupy 100MB then in the worst case real memory usage is around 200MB. I've never suppose that fragmentation could be so significant.

When quite simple memory pools were used, then internal fragmentation has been cut down to 1-2%! Impressive.

Efficient trie representation

While implementing Aho-Corasick algorithm I've checked several trie representations.

Python3: import antigravity

Works fine!

Grafika komputerowa I

Całkiem udany skrypt do grafiki komputerowej autorstwa Przemysława Kiciaka udostępnił UW w ramach swojego portalu z materiałami dydaktycznymi. Obszerna tematyka, więc miejscami skrótowo i ogólnikowo, ale ogólnie wygląda zachęcająco.

PIC Language

Yesterday I made my first diagram with PIC (see Wikipedia) and... I felt in love. Language is just perfect, intuitive and powerful. Try it and you will never use any popular drawing software.

Xorg VESA driver - higher resolutions

Default configuration of VESA driver allows resolutions 640x480 and 800x600.
It is quite simple to get higher resolutions - in section Monitor of /etc/X11/xorg.conf we have to set horizontal and vertical refresh rates. By default these values are set to lowest, safe area.

Here are my settings:

Section "Monitor"
        Identifier   "Monitor0"
        VendorName   "Monitor Vendor"
        ModelName    "Monitor Model"

        HorizSync    42.0 - 80.0
        VertRefresh  55.0 - 100.0 
EndSection

X.org is able to work at 1280x1024 with vertical refresh rate 75Hz. HTH

PostgrSQL: printf in PL/pgSQL

PostgreSQL wiki has entry about sprintf - is is quite simple approach (and isn't marked as immutable), the main drawback is iterating over all chars of format string. Here is a version use strpos to locate % in format string, and it's faster around 2 times:

CREATE OR REPLACE FUNCTION printf2(fmt text, variadic args anyarray) RETURNS text
LANGUAGE plpgsql IMMUTABLE AS $$
   DECLARE
      argcnt  int  := 1;
      head    text := '';     -- result
      tail    text := fmt;    -- unprocessed part
      k       int;
   BEGIN
      LOOP
         k := strpos(tail, '%');
         IF k = 0 THEN
            -- no more '%'
            head := head || tail;
            EXIT;
         ELSE
            IF substring(tail, k+1, 1) = '%' THEN
               -- escape sequence '%%'
               head := head || substring(tail, 1, k);
               tail := substring(tail, k+2);
            ELSE
               -- insert argument
               head := head || substring(tail, 1, k-1) || COALESCE(args[argcnt]::text, '');
               tail := substring(tail, k+1);
               argcnt := argcnt + 1;
            END IF;
         END IF;
      END LOOP;
   RETURN head;
END;
$$;