Suppress beacon sync unless potential actions (#2765)

* Update comments & logs

* Do not start beacon sync unless there is possibly something to do

why:
  It would continue polling without having any effect other than
  logging. Now it will not start unless there is RPC available
  or there was a previously interrupted sync to be resumed.

nimbus/nimbus_desc.nim

@@ -63,8 +63,8 @@ proc stop*(nimbus: NimbusNode, conf: NimbusConf) {.async, gcsafe.} =
     await nimbus.networkLoop.cancelAndWait()
   if nimbus.peerManager.isNil.not:
     await nimbus.peerManager.stop()
-  #if nimbus.snapSyncRef.isNil.not:
+  if nimbus.beaconSyncRef.isNil.not:
-  #  nimbus.snapSyncRef.stop()
+    nimbus.beaconSyncRef.stop()
   if nimbus.metricsServer.isNil.not:
     await nimbus.metricsServer.stop()
 

nimbus/nimbus_execution_client.nim

@@ -110,17 +110,13 @@ proc setupP2P(nimbus: NimbusNode, conf: NimbusConf,
         nimbus.ethNode.peerPool,
         nimbus.chainRef,
         nimbus.txPool)
-    #of ProtocolFlag.Snap:
-    #  nimbus.ethNode.addSnapHandlerCapability(
-    #    nimbus.ethNode.peerPool,
-    #    nimbus.chainRef)
   # Cannot do without minimal `eth` capability
   if ProtocolFlag.Eth notin protocols:
     nimbus.ethNode.addEthHandlerCapability(
       nimbus.ethNode.peerPool,
       nimbus.chainRef)
 
-  # Always start syncer -- will throttle itself unless needed
+  # Always initialise beacon syncer
   nimbus.beaconSyncRef = BeaconSyncRef.init(
     nimbus.ethNode, nimbus.chainRef, conf.maxPeers, conf.beaconChunkSize)
 
@@ -225,7 +221,11 @@ proc run(nimbus: NimbusNode, conf: NimbusConf) =
     setupRpc(nimbus, conf, com, protocols)
 
     if conf.maxPeers > 0:
-      nimbus.beaconSyncRef.start
+      # Not starting syncer if there is definitely no way to run it. This
+      # avoids polling (i.e. waiting for instructions) and some logging.
+      let resumeOnly = not conf.engineApiServerEnabled()
+      if not nimbus.beaconSyncRef.start(resumeOnly):
+        nimbus.beaconSyncRef = BeaconSyncRef(nil)
 
     if nimbus.state == NimbusState.Starting:
       # it might have been set to "Stopping" with Ctrl+C

nimbus/sync/beacon.nim

@@ -14,7 +14,7 @@ import
   pkg/[chronicles, chronos, eth/p2p, results],
   pkg/stew/[interval_set, sorted_set],
   ../core/chain,
-  ./beacon/[worker, worker_desc],
+  ./beacon/[worker, worker_desc, worker/db],
   "."/[sync_desc, sync_sched, protocol]
 
 logScope:
@@ -62,16 +62,20 @@ proc init*(
   var desc = T()
   desc.initSync(ethNode, maxPeers)
   desc.ctx.pool.nBodiesBatch = chunkSize
-  # Initalise for `persistBlocks()`
   desc.ctx.pool.chain = chain
   desc
 
-proc start*(ctx: BeaconSyncRef) =
+proc start*(desc: BeaconSyncRef; resumeOnly = false): bool =
-  ## Beacon Sync always begin with stop mode
+  ## Start beacon sync. If `resumeOnly` is set `true` the syncer will only
-  doAssert ctx.startSync()      # Initialize subsystems
+  ## start up if it can resume work, e.g. after being previously interrupted.
+  if resumeOnly:
+    desc.ctx.dbLoadSyncStateLayout()
+    if not desc.ctx.layout.headLocked:
+      return false
+  desc.startSync()
 
-proc stop*(ctx: BeaconSyncRef) =
+proc stop*(desc: BeaconSyncRef) =
-  ctx.stopSync()
+  desc.stopSync()
 
 # ------------------------------------------------------------------------------
 # End

nimbus/sync/beacon/worker/start_stop.nim

@@ -98,7 +98,7 @@ proc setupDatabase*(ctx: BeaconCtxRef) =
   # Load initial state from database if there is any
   ctx.dbLoadSyncStateLayout()
 
-  # Set blocks batch import value for `persistBlocks()`
+  # Set blocks batch import value for block import
   if ctx.pool.nBodiesBatch < nFetchBodiesRequest:
     if ctx.pool.nBodiesBatch == 0:
       ctx.pool.nBodiesBatch = nFetchBodiesBatchDefault

nimbus/sync/beacon/worker/start_stop/ticker.nim

@@ -18,7 +18,7 @@ import
   ../helpers
 
 logScope:
-  topics = "ticker"
+  topics = "beacon ticker"
 
 type
   TickerStatsUpdater* = proc: TickerStats {.gcsafe, raises: [].}
@@ -108,10 +108,10 @@ proc tickerLogger(t: TickerRef) {.gcsafe.} =
     t.visited = now
 
     if data.stored == data.base:
-      info "Sync state", up, peers,
+      debug "Sync state", up, peers,
         B, L, C, D, F, H, T, hS, hU, bS, bU, rrg, mem
     else:
-      info "Sync state", up, peers,
+      debug "Sync state", up, peers,
         S=data.stored.bnStr,
         B, L, C, D, F, H, T, hS, hU, bS, bU, rrg, mem
 

nimbus/sync/beacon/worker_desc.nim

@@ -130,7 +130,7 @@ type
     blkSync*: BlocksImportSync       ## For importing/executing blocks
     nextUpdate*: Moment              ## For updating metrics
 
-    # Blocks import/execution settings for running  `persistBlocks()` with
+    # Blocks import/execution settings for importing with
     # `nBodiesBatch` blocks in each round (minimum value is
     # `nFetchBodiesRequest`.)
     chain*: ForkedChainRef           ## Database