Segment of pages causes crash in Apache and help with segments

I hope you can help me as I’m trying to create and use a segment.

I have four web pages that I want to see statisics for.
I create a new segment and choose under Events- “Page URL” IS and then the url, for exampel
I then add an OR condition and choose another “Page URL” IS and then the next url.
I do this four times as I want the segment to cover four pages.
But the segment does not work, I don’t get any statistics about visitors to these pages. What am I doing wrong?
Grateful for any tips here, thanks!

Often when I have created and tested the segments I have experienced a race condition causing the Apache to break down, and Piwik crashes. We have to restart Apache and then Piwik works again. Is this something you have noticed or heard of?

Thanks already for any hints!
Best regards,