target readahead to max 5% instead of 100%

Author: mafintosh

lib/prefetcher.js

@@ -1,12 +1,15 @@
 // should move to hypercore itself
 
+const MAX_READAHEAD_TARGET = 0.05 // aim to buffer 5% always
+
 module.exports = class Prefetcher {
   constructor (core, { max = 64, start = 0, end = core.length, linear = true } = {}) {
     this.core = core
     this.max = max
     this.range = null
     this.startBound = start
     this.endBound = end
+    this.maxReadAhead = Math.max(max * 2, Math.floor((end - start) * MAX_READAHEAD_TARGET))
 
     this.start = start
     this.end = start
@@ -48,6 +51,7 @@ module.exports = class Prefetcher {
       this.missing++
     }
 
+    if (end > this.start + this.maxReadAhead) end = this.start + this.maxReadAhead
     if (end >= this.endBound) end = this.endBound
 
     this.end = end