Add bench test for large core with two non-sparse readers

package.json

@@ -58,6 +58,7 @@
   },
   "devDependencies": {
     "brittle": "^3.0.0",
+    "byte-size": "^8.1.1",
     "hyperswarm": "^4.3.6",
     "random-access-memory": "^6.1.0",
     "random-access-memory-overlay": "^3.0.0",

test/bench/large.js

@@ -0,0 +1,70 @@
+const test = require('brittle')
+const Hypercore = require('../../index.js')
+const RAM = require('random-access-memory')
+const { replicate, createTmpDir } = require('../helpers')
+const speedometer = require('speedometer')
+const byteSize = require('byte-size')
+
+test('large core with two non-sparse readers', { timeout: 999999999 }, async function (t) {
+  const dir = createTmpDir(t)
+
+  const writer = new Hypercore(dir)
+  await writer.ready()
+
+  const clone1 = new Hypercore(RAM, writer.key)
+  const clone2 = new Hypercore(RAM, writer.key)
+
+  for (let i = writer.length; i < 1000000; i++) {
+    await writer.append(Math.random().toString(16).substr(2))
+
+    if (i % 100000 === 0) t.comment('Append ' + i)
+  }
+
+  t.comment('Writer complete')
+
+  intervalSpeed(t, writer, 'Writer')
+  intervalSpeed(t, clone1, 'Clone1')
+  intervalSpeed(t, clone2, 'Clone2')
+
+  replicate(writer, clone1, t)
+  replicate(writer, clone2, t)
+
+  const dl1 = clone1.download()
+  const dl2 = clone2.download()
+
+  await dl1.done()
+  await dl2.done()
+
+  t.comment('Done')
+
+  await writer.close()
+  await clone1.close()
+  await clone2.close()
+})
+
+function intervalSpeed (t, core, name) {
+  const info = {
+    blocks: { down: speedometer(), up: speedometer() },
+    network: { down: speedometer(), up: speedometer() }
+  }
+
+  core.on('download', onspeed.bind(null, 'down', info))
+  core.on('upload', onspeed.bind(null, 'up', info))
+
+  const id = setInterval(() => {
+    t.comment(
+      name,
+      '↓ ' + Math.ceil(info.blocks.down()),
+      '↑ ' + Math.ceil(info.blocks.up()) + ' blks/s',
+      '↓ ' + byteSize(info.network.down()),
+      '↑ ' + byteSize(info.network.up())
+    )
+  }, 1000)
+
+  t.teardown(() => clearInterval(id))
+}
+
+function onspeed (eventName, info, index, byteLength, from) {
+  info.blocks[eventName](1)
+  info.network[eventName](byteLength)
+}