fix(gatsby): [loki] sync db autosaves (#10212)

This PR orchestrates the saving of db state for both loki and redux into one place. Previously, loki would use its `autosave` feature and save to disk every 1000ms. Whereas now, it uses the same style as `gatsby/redux` where a debounced save is triggered for each new event. 

Note that both database save asynchronously (redux's write to disk is async) so this isn't a perfect "Stop the world" synchronized save. However it's better than it was before.

packages/gatsby/src/bootstrap/index.js

@@ -21,6 +21,7 @@ const getConfigFile = require(`./get-config-file`)
 const tracer = require(`opentracing`).globalTracer()
 const preferDefault = require(`./prefer-default`)
 const nodeTracking = require(`../db/node-tracking`)
+require(`../db`).startAutosave()
 
 // Show stack trace on unhandled promises.
 process.on(`unhandledRejection`, (reason, p) => {

packages/gatsby/src/db/index.js

@@ -0,0 +1,50 @@
+const _ = require(`lodash`)
+const redux = require(`../redux`)
+const { emitter } = redux
+
+// Even if we are using loki, we still include redux in the list of
+// dbs since it still has pages, config, etc.
+const dbs = [redux]
+if (process.env.GATSBY_DB_NODES === `loki`) {
+  dbs.push(require(`./loki`))
+}
+
+// calls `saveState()` on all DBs
+function saveState() {
+  for (const db of dbs) {
+    db.saveState()
+  }
+}
+const saveStateDebounced = _.debounce(saveState, 1000)
+
+/**
+ * Sets up listeners so that once bootstrap has finished, all
+ * databases save their state to disk. If we're in `develop` mode,
+ * then any new event triggers a debounced save as well.
+ */
+function startAutosave() {
+  // During development, once bootstrap is finished, persist state on changes.
+  let bootstrapFinished = false
+  if (process.env.gatsby_executing_command === `develop`) {
+    emitter.on(`BOOTSTRAP_FINISHED`, () => {
+      bootstrapFinished = true
+      saveState()
+    })
+    emitter.on(`*`, () => {
+      if (bootstrapFinished) {
+        saveStateDebounced()
+      }
+    })
+  }
+
+  // During builds, persist state once bootstrap has finished.
+  if (process.env.gatsby_executing_command === `build`) {
+    emitter.on(`BOOTSTRAP_FINISHED`, () => {
+      saveState()
+    })
+  }
+}
+
+module.exports = {
+  startAutosave,
+}

packages/gatsby/src/db/loki/index.js

@@ -71,8 +71,6 @@ function startFileDb(saveFile) {
           resolve()
         }
       },
-      autosave: true,
-      autosaveInterval: 1000,
     }
     db = new loki(saveFile, dbOptions)
   })
@@ -109,6 +107,24 @@ async function start({ saveFile } = {}) {
   ensureNodeCollections(db)
 }
 
+// Saves the database to disk and returns a promise that will be
+// resolved once the save has finished
+function saveState() {
+  return new Promise((resolve, reject) => {
+    if (db) {
+      db.saveDatabase(err => {
+        if (err) {
+          console.log(`error saving loki DB`)
+          console.log(err)
+          reject(err)
+        } else {
+          resolve()
+        }
+      })
+    }
+  })
+}
+
 /**
  * Returns a reference to the database. If undefined, the db has not been
  * initalized yet. Call `start()`
@@ -123,4 +139,5 @@ module.exports = {
   start,
   getDb,
   colls,
+  saveState,
 }

packages/gatsby/src/redux/index.js

@@ -63,7 +63,8 @@ const store = Redux.createStore(
 )
 
 // Persist state.
-const saveState = state => {
+function saveState() {
+  const state = store.getState()
   const pickedState = _.pick(state, [
     `nodes`,
     `status`,
@@ -85,34 +86,14 @@ const saveState = state => {
     () => {}
   )
 }
-const saveStateDebounced = _.debounce(saveState, 1000)
+
+exports.saveState = saveState
 
 store.subscribe(() => {
   const lastAction = store.getState().lastAction
   emitter.emit(lastAction.type, lastAction)
 })
 
-// During development, once bootstrap is finished, persist state on changes.
-let bootstrapFinished = false
-if (process.env.gatsby_executing_command === `develop`) {
-  emitter.on(`BOOTSTRAP_FINISHED`, () => {
-    bootstrapFinished = true
-    saveState(store.getState())
-  })
-  emitter.on(`*`, () => {
-    if (bootstrapFinished) {
-      saveStateDebounced(store.getState())
-    }
-  })
-}
-
-// During builds, persist state once bootstrap has finished.
-if (process.env.gatsby_executing_command === `build`) {
-  emitter.on(`BOOTSTRAP_FINISHED`, () => {
-    saveState(store.getState())
-  })
-}
-
 /** Event emitter */
 exports.emitter = emitter