kibana/docs/extend/plugin-performance.md

mapped_pages
https://www.elastic.co/guide/en/kibana/current/plugin-performance.html

Keep Kibana fast [plugin-performance]

tl;dr: Load as much code lazily as possible. Everyone loves snappy applications with a responsive UI and hates spinners. Users deserve the best experience whether they run {{kib}} locally or in the cloud, regardless of their hardware and environment.

There are 2 main aspects of the perceived speed of an application: loading time and responsiveness to user actions. {{kib}} loads and bootstraps all the plugins whenever a user lands on any page. It means that every new application affects the overall loading performance, as plugin code is loaded eagerly to initialize the plugin and provide plugin API to dependent plugins.

However, it’s usually not necessary that the whole plugin code should be loaded and initialized at once. The plugin could keep on loading code covering API functionality on {{kib}} bootstrap, but load UI related code lazily on-demand, when an application page or management section is mounted. Always prefer to import UI root components lazily when possible (such as in mount handlers). Even if their size may seem negligible, they are likely using some heavy-weight libraries that will also be removed from the initial plugin bundle, therefore, reducing its size by a significant amount.

import type { Plugin, CoreSetup, AppMountParameters } from '@kbn/core/public';
export class MyPlugin implements Plugin<MyPluginSetup> {
  setup(core: CoreSetup, plugins: SetupDeps) {
    core.application.register({
      id: 'app',
      title: 'My app',
      async mount(params: AppMountParameters) {
        const { mountApp } = await import('./app/mount_app');
        return mountApp(await core.getStartServices(), params);
      },
    });
    plugins.management.sections.section.kibana.registerApp({
      id: 'app',
      title: 'My app',
      order: 1,
      async mount(params) {
        const { mountManagementSection } = await import('./app/mount_management_section');
        return mountManagementSection(coreSetup, params);
      },
    });
    return {
      doSomething() {},
    };
  }
}

Understanding plugin bundle size [_understanding_plugin_bundle_size]

{{kib}} Platform plugins are pre-built with @kbn/optimizer and distributed as package artifacts. This means that it is no longer necessary for us to include the optimizer in the distributable version of {{kib}}. Every plugin artifact contains all plugin dependencies required to run the plugin, except some stateful dependencies shared across plugin bundles via @kbn/ui-shared-deps-npm and @kbn/ui-shared-deps-src. This means that plugin artifacts tend to be larger than they were in the legacy platform. To understand the current size of your plugin artifact, run @kbn/optimizer with:

node scripts/build_kibana_platform_plugins.js --dist --profile --focus=my_plugin

and check the output in the target sub-folder of your plugin folder:

ls -lh plugins/my_plugin/target/public/
# output
# an async chunk loaded on demand
... 262K 0.plugin.js
# eagerly loaded chunk
... 50K  my_plugin.plugin.js

You might see at least one js bundle - my_plugin.plugin.js. This is the only artifact loaded by {{kib}} during bootstrap in the browser. The rule of thumb is to keep its size as small as possible. Other lazily loaded parts of your plugin will be present in the same folder as separate chunks under {{number}}.myplugin.js names. If you want to investigate what your plugin bundle consists of, you need to run @kbn/optimizer with --profile flag to generate a webpack stats file.

node scripts/build_kibana_platform_plugins.js --dist --no-examples --profile

Many OSS tools allow you to analyze the generated stats file:

• An official tool from Webpack authors
• webpack-visualizer