Increasing CPU spikes over time with session-file-store

Question

On Feb 19 or so, my server started to exhibit hourly increasing CPU spikes:

I traced these to the node process which serves my website. Git shows no changes between Jan 12 and Feb 24. On Feb 24 I made the following upgrades:

-    "mongoose": "^4.11.6",
+    "mongoose": "^5.9.2",
-    "passport-local-mongoose": "^4.1.0",
+    "passport-local-mongoose": "^6.0.1",
-    "jwt-simple": "^0.5.1",
+    "jwt-simple": "^0.5.6",
-    "orm": "^5.0.2",
+    "orm": "^5.0.5",

By July my CPU was spending all its time at 100%

Some profiling revealed that session-file-store is either responsible or is being called by the responsible code:

Here's the call tree, which is probably informative, though I don't really understand it

The code in which I set up session-file-store is

const next = require("next")
const express = require("express")
const passport = require("passport")
const session = require("express-session")
const FileStore = require("session-file-store")(session)

const app = next({
  dir: ".",
  dev: config.dev
})

app
  .prepare()
  .then(() => {
    server = express()

    server.use(cookieParser())
    server.use(
      session({
        secret: process.env.SESSION_SECRET,
        store: new FileStore({
          path: "/tmp/sessions",
          secret: process.env.SESSION_SECRET
        }),
        resave: false,
        rolling: true,
        saveUninitialized: true,
        httpOnly: true,
        cookie: {
          maxAge: 60000 * 60 * 24 * 7 * 4 // 4 weeks
        }
      })
    )
    server.use(passport.initialize())
    server.use(passport.session())
    passportConfig(passport)

Does something in my configuration explain why session-file-store would have an hourly task with perpetually increasing volume? Is this a passport-local-mongoose bug?

Answer 1

The problem was that I was using the session option saveUninitialized. This was causing a huge buildup of useless session files, which are processed hourly in some way.

I solved the problem by setting saveUninitialized to false.