After switching on 10% mirroring of the traffic the actual request rate to Parsoid-PHP is already 50% of Parsoid-JS. The problem is that the mirrored traffic doesn't account for storage, thus if we continue wrapping up percentage of mirrored traffic, we will likely overload PHP parsoid. WE should either only mirror update traffic (check for cache-control: no-cache), switch on storage for PHP parsoid ( according to @ssastry we don't store PHP Parsoid now ), or be smart about mirroring traffic depending on whether JS parsoid output is in storage.