Tadek’s Blog

Cool. It looks that PostgreSQL8.0 supports XML as an additional extension (contrib driectory). In gentoo you can compile it specifying +xml2 option.

Now how to use it: 1. you need to create xml functions in a database using a supplied script, most typically /usr/share/postgresql/contrib/pgxml.sql. Note that this script has been created (customized) by autoconf and contains a hard-coded location of your pgxml.so library, typically: /usr/lib/postgresql/pgxml.so.

1. If you get no error…. well that’s it

See this link and the documentation contrib/xml2 for more details.

BTW: If your database stores XML as binary strings (bytea) you must convert them to normal strings using encode(<byteacolumn>, ‘escape’);

Postgres is strange. If you make a query

select min(column_with_index) from table;

the database performs a sequential scan – you can only imagine how long it takes on a 10M record database. This seems to be a feature (!@!#!@), but indices can will used if you use the following workaround:

select column_with_index from table order by 1 (desc) limit 1;

This trick is explained here.

After almost a day of editing and reorganizing, I think the blog is ready to go on-line. Many things are really chaotic, I nonetheless hope that someone might find something useful here.

I also did some minor patching of WP, making future updates will be close to impossible. Hope it will not be that bad…

To summarize today’s changes: 1. “linky” category, inspired by Diego’s blog, which was inspired by Fernando Graphicos, inspired by….

I basically followed Fernando’s suggestions, shamelessly stealing some of Diego’s CSS (not too much though). The changes I had to make included editing of all the files containing a loop “while(have_posts()…”.

1. Displaying hierarchical categories, instead of the flat strucutre. The change was to change “hierarchical=0″ to “hierarchical=1″ in sidebar.php.

2. Displaying proper categories, depending on the current user. This was a bit tricky one: Depending on the user logged in, I wanted to have the correct list of categories on the main page. The patch is one line in template-functions-category.php”:

Replacing the line (somewhere around line 290): WHERE post_status = ‘publish’ with WHERE ( post_status = ‘publish’”. (($user_ID)?” or (post_status=’private’ AND post_author = $user_ID)”:”") . “)

Also $user_ID has to be declared as global somewhere before.

1. (FAILED) Correct counting of categories. With a hierarchical system, I wanted to have a correct number of categories, e.g. if category A (5) has two sub categories A1 (2) and A2 (7), I would like A to be displayed as (14) or (5/9), as this is the number of posts you’d see if you click on it. … or is it?

I implemented is as follows: - storing a hash table of parent nodes while reading the categories (line 275) - updating the total number of posts by summing it up the chain (while ($id = $parent[$id])) {} (line 295).

This would have worked, but it has a BIG problem: a post can have both categories A and A1 set and thus would be counted twice. To avoid this, one would have to change the entire logic of a query: A single SQL query would have to be replaced by 2*n queries (for each category, querying the child categories -> using get_category_children() from classes.php) and then querying the number of posts in each of the categories. While it would have been feasible, I thought it’s not worth it and I gave up.

A cool link: http://www.dogma.net/markn/articles/Permutations/

In essence the algorithm works as follows:

1. start looking from the end of the sequence for two consecutive values i and ii such that i < ii.
2. start looking from the end of the sequence for the value j greater that i (the worst case getting ii or earlier).
3. swap i and j
4. reverse the sequence ii to last.

Examples:

123 -> i  = 2, ii = 3, j = 3  -> 132
132 -> i=1,ii=2,j=3 -> 213
213 -> i=2;ii=3;j=3 -> 231
231 -> i=1;ii=2;j=2 -> 312
312 -> i=2;ii=3;j=3 -> 321
321 - END

It also generates only unique permutations if there are some duplicates in the sequence (e.g. AAABBB) Cool!

(thanks to Diego): perl -ne ‘while ((/condition/g)) { print “something”; }’

Use flip:

flip -u <file_name> flip -m <file_name>

apt-get install flip