0.3 GB idle, against 0.43 to 1.8 GB.

Memory for every configuration.

A host sizes a server by memory. We measured both stacks under full load and again 30 seconds after the load stopped, on the same site with all plugins active, counting memory shared between processes once. We ran WordPress two ways so pool size does not rig the comparison: a tuned static 64 children pool and a right-sized dynamic, 8 children pool. Memory was measured on BookPress 0.2.57.

Memory measured on BookPress 0.2.57, 13 October 2026. WordPress ran PHP-FPM with OPcache and JIT, MariaDB, a Redis object cache and nginx. Neither side used a page cache. The throughput figures on the speed page are a later and separate measurement, on BookPress 0.2.64.

Idle is the density figure. Thirty seconds after the load stops, four BookPress workers release to about 0.3 GB; a right-sized WordPress holds 0.43 GB and a tuned 64-child pool holds 1.8 GB. A host packs mostly-idle sites, so the memory a site hands back between visitors is the memory another site can use.

More workers. Engine code and plugin bytecode load once and are shared by every worker; each additional worker then adds its own working set under load and gives most of it back when idle. A worker that has had no request for 30 seconds gives memory back to the system; a WordPress pool holds what it preforked.

Memory that comes back between visitors.

Under load the same site takes about 0.6 GB on four BookPress workers, close to a right-sized WordPress and a third of a tuned pool. Idle, it releases to about 0.3 GB while the WordPress pools hold. The many-sites saving is this idle release, not a near-free worker. The sites keep their themes, their /wp-admin and their URLs.