[enh] #1325 Allow to have up to 10 chunks of advance compared to apply during sync

app/modules/crawler/lib/constants.ts

@@ -32,6 +32,7 @@ export const CrawlerConstants = {
   SANDBOX_CHECK_INTERVAL: 48, // Every 4 hours (288 blocks a day / 24 * 4)
   TEST_PEERS_INTERVAL: 10, // In seconds
   SYNC_PEERS_INTERVAL: 3, // Every 3 block average generation time
+  SYNC_CHUNKS_IN_ADVANCE: 10, // We want to have that much chunks in advance when syncing
 
   DURATIONS: {
     TEN_SECONDS: 10,

app/modules/crawler/lib/sync/v2/DownloadStream.ts

@@ -132,13 +132,10 @@ export class DownloadStream extends Duplex {
         delete this.chunks[this.currentChunkNumber]
         // Let's start the download of next chunk
         this.currentChunkNumber++
-        this.downloadChunk(this.currentChunkNumber)
-          .then(() => this.downloadChunk(this.currentChunkNumber + 1))
-          .then(() => this.downloadChunk(this.currentChunkNumber + 2))
-          .then(() => this.downloadChunk(this.currentChunkNumber + 3))
-          .then(() => this.downloadChunk(this.currentChunkNumber + 4))
-          .then(() => this.downloadChunk(this.currentChunkNumber + 5))
-          .then(() => this.downloadChunk(this.currentChunkNumber + 6))
+        let p = this.downloadChunk(this.currentChunkNumber)
+        for (let i = 1; i <= CrawlerConstants.SYNC_CHUNKS_IN_ADVANCE; i++) {
+          p = p.then(() => this.downloadChunk(this.currentChunkNumber + i))
+        }
       }
       else {
         // We don't have it yet