Disable background workers (#948)

* disable background workers with params

Author: tdrz

.changeset/soft-carpets-kneel.md

@@ -0,0 +1,5 @@
+---
+'@electric-sql/pglite': patch
+---
+
+Disable background workers.

docs/components/Repl.vue

@@ -6,6 +6,11 @@ import { PGlite } from '@electric-sql/pglite'
 import { vector } from '@electric-sql/pglite/vector'
 
 const pg = new PGlite({
+  startParams: [
+    ...PGlite.defaultStartParams,
+    '-c',
+    'application_name=PGlite REPL',
+  ],
   extensions: {
     vector,
   },

docs/docs/api.md

@@ -90,6 +90,21 @@ Path to the directory for storing the Postgres database. You can provide a URI s
   })
   ```
 
+- `startParams?: string[]` <br />
+  An array of strings that will be passed to the Postgres process. This is the set of parameters one would pass to a native PostgreSQL instance.
+
+  ```ts
+  import { PGlite } from '@electric-sql/pglite'
+
+  const pg = await PGlite.create({
+    startParams: [
+      ...PGlite.defaultStartParams,
+      '-c',
+      'application_name=My awesome backend',
+    ],
+  })
+  ```
+
 #### `options.extensions`
 
 PGlite and Postgres extensions are loaded into a PGLite instance on start, and can include both a WASM build of a Postgres extension and/or a PGlite client plugin.

docs/repl/ReplPlayground.vue

@@ -53,6 +53,11 @@ async function loadPg() {
   try {
     console.log(`Creating PGlite instance with idb://${dbName}`)
     return await PGlite.create({
+      startParams: [
+        ...PGlite.defaultStartParams,
+        '-c',
+        'application_name=PGlite REPL Playground',
+      ],
       dataDir: `idb://${dbName}`,
       extensions,
     })
@@ -93,7 +98,7 @@ async function loadPg() {
 }
 
 onMounted(async () => {
-  pg.value = await loadPg()
+  doLoadPg()
 })
 
 const rootStyle = window.getComputedStyle(document.body)
@@ -179,7 +184,7 @@ async function clearDb() {
     if (closed) break
     await new Promise((resolve) => setTimeout(resolve, 10))
   }
-  pg.value = await loadPg()
+  doLoadPg()
 }
 </script>
 

packages/pglite/src/pglite.ts

@@ -123,6 +123,12 @@ export class PGlite
     'exit_on_error=false',
     '-c',
     'log_checkpoints=false',
+    '-c',
+    'max_worker_processes=0',
+    '-c',
+    'max_parallel_workers=0',
+    '-c',
+    'max_parallel_workers_per_gather=0',
   ]
 
   /**

packages/pglite/tests/basic.test.ts

@@ -650,5 +650,45 @@ await testEsmCjsAndDTC(async (importType) => {
         current_role: 'postgres',
       })
     })
+
+    // this tests the parameter 'max_parallel_workers_per_gather=0',
+    it('it shouldnt use parallel workers on gather', async () => {
+      const db = await PGlite.create()
+
+      const ROWS = 400_000
+
+      await db.exec(`
+        CREATE TABLE t (id SERIAL PRIMARY KEY, val TEXT);
+        INSERT INTO t (val)
+          SELECT md5(i::text) FROM generate_series(1, ${ROWS}) AS i;
+      `)
+
+      // when using workers for GATHER, the query plans contains Gather
+      const plan = await db.query('EXPLAIN SELECT COUNT(*) FROM t')
+
+      const hasGather = plan.rows.some((r: any) =>
+        r['QUERY PLAN'].includes('Gather'),
+      )
+      expect(hasGather).toBeFalsy()
+
+      const result = await db.query<any>('SELECT COUNT(*) FROM t')
+      expect(result.rows[0].count).toEqual(ROWS)
+    })
+
+    it('altering startParams should work"', async () => {
+      const dateTime = Date.now().toString()
+      const db = await PGlite.create({
+        startParams: [
+          ...PGlite.defaultStartParams,
+          '-c',
+          `application_name=${dateTime}`,
+        ],
+      })
+
+      const databaseAndRole = await db.exec(
+        `SELECT setting FROM pg_settings WHERE name='application_name'`,
+      )
+      expect(databaseAndRole[0].rows[0].setting).toEqual(dateTime)
+    })
   })
 })