In multi-tenant mode ePHPm serves every site in sites_dir from one process. Every tenant’s PHP runs as the same OS user on the same pool of ZTS threads. A thread that just served blog.example will serve shop.example a few milliseconds later. That’s the density win. It also means the kernel has no idea which tenant is behind a given connect(). As far as Linux is concerned it’s all ephpm-web.

ePHPm v0.7.0 shipped per-site multi-tenancy. Point [server] sites_dir at a directory and every Host maps to its own docroot and its own Turso database file. One process serves all of them. The first question anybody asks about that is “how many sites fit on a box?” The honest way to answer it is to turn the question around. What does one more site cost? If you know the marginal RAM, file descriptors, CPU and disk for a tenant, the box size falls out of arithmetic.

Ask most people what their PHP server does when it’s overloaded and you’ll hear “it returns 503s.” Ask them how they know and it usually comes down to a config setting they read about. I was in that camp for ePHPm. We had a [server.limits] max_connections knob, and the docs said it returned 503 at the cap. Every benchmark we had ever run reported zero errors under heavy load. Then I wrote a load generator that could produce overload. The honest answer was that an…

I do most of my benchmarking on a Windows box in WSL2. It’s the machine on my desk with 32 threads and 62 GB of RAM. Everybody who does that learns the first rule early: don’t put your data on /mnt/c. DrvFs is the 9p-backed mount that exposes the Windows drives inside WSL, and it’s slow for file-heavy work. So the databases, the docroot and the build output all live on the WSL ext4 disk. My scaling harness for ePHPm even says so in capital letters in its README.

Part 1 ended with ePHPm running two SQLite engines. rusqlite ran in-process for a single node, and an embedded sqld child process ran for a cluster. The sidecar fell off a cliff past four concurrent writers. The best fix I could ship was a semaphore set to 1. This post is about replacing both engines with one, and about how I decided that engine was ready.

Every PHP deployment I’ve run eventually grew a Redis. Sessions, the WordPress object cache, Laravel’s cache and locks, rate limiting. ePHPm is supposed to be one binary that replaces nginx + php-fpm + Redis, so it needed a cache in the box. I didn’t want to write one. This post covers why I did anyway and how it’s built. It also covers the bug that sat in its eviction code from March until last month. Then I compare it against a stock Redis on the same machine with…

Last month I wrote about running SQLite behind a MySQL socket with litewire. I ended on “passing an install suite is not the same thing as behaving like MySQL”. That turned out to be accurate. On August 10th a few things happened at once:

The scariest response a server can send isn’t a 500. It’s a 200 that should have been a 500. A crash is loud. The pod restarts, an alert fires, somebody looks. A truncated page with a success status code is quiet. Your CDN caches it and the health check calls the box healthy. A client parses half a document as if it were the whole thing.

PHP’s share-nothing model is one of its best properties. It has one expensive side effect: a request can’t keep a database connection for the next request. php-fpm gives you PDO::ATTR_PERSISTENT and mysqli’s p: hosts. But those are per-worker-process. PDO’s keep whatever session state the last request left behind. mysqli at least resets the session with COM_CHANGE_USER on reuse. And almost nobody turns them on. So in practice every PHP request does a TCP connect, a MySQL…

Most PHP sites I have run in the last twenty years did not need a MySQL server. They needed a database, and MySQL was the one every framework spoke. With ePHPm I have been trying to get rid of that server for the common case. The piece that makes it possible is litewire. PHP connects with plain pdo_mysql. litewire speaks the MySQL wire protocol, and the queries land in a SQLite file. WordPress and Laravel don’t know the difference. No mysqld, no child processes, just ephpm and a .db file.