fix(pg): mark client not queryable when a FATAL ends the session

packages/pg/lib/client.js

@@ -438,6 +438,12 @@ class Client extends EventEmitter {
     if (activeQuery.name) {
       delete this.connection.submittedNamedStatements[activeQuery.name]
     }
+    // a FATAL error ends the session; the backend closes the socket and
+    // the client must not be handed out from a pool again. Set the flag
+    // before reporting so error handlers that release() see the dead client
+    if (msg.severity === 'FATAL' || msg.severityNonLocalized === 'FATAL') {
+      this._queryable = false
+    }
     activeQuery.handleError(msg, this.connection)
   }
 

packages/pg/test/unit/client/fatal-session-tests.js

@@ -0,0 +1,43 @@
+'use strict'
+const helper = require('./test-helper')
+const Query = require('../../../lib/query')
+const assert = require('assert')
+
+const suite = new helper.Suite()
+
+suite.test('marks client not queryable when an active query gets a FATAL error', function (done) {
+  const client = helper.client()
+  assert.equal(client._queryable, true)
+  client.connection.emit('readyForQuery')
+
+  client.query(
+    new Query({
+      text: 'select pg_sleep(30)',
+      callback: function (err) {
+        assert.equal(err.severity, 'FATAL')
+        assert.equal(client._queryable, false)
+        done()
+      },
+    })
+  )
+
+  client.connection.emit('errorMessage', { severity: 'FATAL', code: '57P01' })
+})
+
+suite.test('keeps client queryable for a non-FATAL error', function (done) {
+  const client = helper.client()
+  client.connection.emit('readyForQuery')
+
+  client.query(
+    new Query({
+      text: 'select 1',
+      callback: function (err) {
+        assert.equal(err.severity, 'ERROR')
+        assert.equal(client._queryable, true)
+        done()
+      },
+    })
+  )
+
+  client.connection.emit('errorMessage', { severity: 'ERROR', code: '42601' })
+})