Is using %postname% for permalinks really that bad for performance?

This is much more complex than looking up string versus integer. WordPress sifts permalink through a set of persistent regexp-based rules. And it affects logic a lot that string might be many more things than number. See one of better writeups on topic for details.

Practical point to know – this doesn’t concern most sites, except those that have many pages (like PAGE pages, not posts).

Even better point to know – this is all getting fixed in WP 3.3 and will be thing of the past.

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