If we use -namespace for namespace filtering,
will go through ALL pages, THEN the result is filtered by a namespace generator. This may MULTIPLY the running time in some cases and this may cost hours or even days for a fix of complicated, slow regexes.
I have just checked, that dump does contain namespace informátion. So why don't we filter during the scan?
I made an experiment. I modified my copy to display count of articles and count of matching pages. The replacement was:
which seems pretty slow. :-(
The bot scanned the latest huwiki dump for 14 hours(!). (Not the whole dump, I used -xmlstart.) It went through 820 thousand pages and found 240+ matches (I displayed every 10th match).
Then the bot worked further 30-40 minutes to check the actual pages from live wiki, this time with namespace filtering on. (I don't replace in this phase, just save the list, so no human interaction is implied in this time.)
Guess the result! 62 out of 240 remained. This means that the bigger part of these 14 hours went into /dev/null.
Now I realize how much time I wasted in the past 10 years. :-(
I am sure that passing namespaces to