Sort subkey lookups by VertexID when computing keys (#2918)

Since data is ordered by VertexID on disk, with this simple trick we can
make much better use of the various rocksdb caches.

Computing the state root of the full mainnet state is down to 4 hours
(from 9) on my laptop.

nimbus/db/aristo/aristo_compute.nim

@@ -128,18 +128,30 @@ proc getKey(
   else:
     ?db.getKeyRc(rvid, {})
 
+template childVid(v: VertexRef): VertexID =
+  # If we have to recurse into a child, where would that recusion start?
+  case v.vType
+  of Leaf:
+    if v.lData.pType == AccountData and v.lData.stoID.isValid:
+      v.lData.stoID.vid
+    else:
+      default(VertexID)
+  of Branch:
+    v.startVid
+
 proc computeKeyImpl(
     db: AristoDbRef,
     rvid: RootedVertexID,
     batch: var WriteBatch,
-    vtxl: (VertexRef, int),
+    vtx: VertexRef,
+    level: int,
     skipLayers: static bool,
 ): Result[(HashKey, int), AristoError] =
   # The bloom filter available used only when creating the key cache from an
   # empty state
 
   # Top-most level of all the verticies this hash computation depends on
-  var (vtx, level) = vtxl
+  var level = level
 
   # TODO this is the same code as when serializing NodeRef, without the NodeRef
   var writer = initRlpWriter()
@@ -160,9 +172,12 @@ proc computeKeyImpl(
                     if keyvtxl[0][0].isValid:
                       (keyvtxl[0][0], keyvtxl[1])
                     else:
-                      let vtxl = (keyvtxl[0][1], keyvtxl[1])
                       ?db.computeKeyImpl(
-                        (stoID.vid, stoID.vid), batch, vtxl, skipLayers = skipLayers
+                        (stoID.vid, stoID.vid),
+                        batch,
+                        keyvtxl[0][1],
+                        keyvtxl[1],
+                        skipLayers = skipLayers,
                       )
                 level = maxLevel(level, sl)
                 skey
@@ -179,30 +194,67 @@ proc computeKeyImpl(
           # TODO avoid memory allocation when encoding storage data
           rlp.encode(vtx.lData.stoData)
     of Branch:
-      # For branches, we need to load the verticies before recursing into them
+      # For branches, we need to load the vertices before recursing into them
       # to exploit their on-disk order
       var keyvtxs: array[16, ((HashKey, VertexRef), int)]
       for n, subvid in vtx.pairs:
         keyvtxs[n] = ?db.getKey((rvid.root, subvid), skipLayers)
 
-      template writeBranch(w: var RlpWriter): HashKey =
+      # Make sure we have keys computed for each hash
-        w.encodeBranch(vtx):
+      block keysComputed:
-          if subvid.isValid:
+        while true:
-            batch.enter(n)
+          # Compute missing keys in the order of the child vid that we have to
-            let (bkey, bl) =
+          # recurse into, again exploiting on-disk order - this more than
-              if keyvtxs[n][0][0].isValid:
+          # doubles computeKey speed on a fresh database!
-                (keyvtxs[n][0][0], keyvtxs[n][1])
+          var
-              else:
+            minVid = default(VertexID)
+            minIdx = keyvtxs.len + 1 # index where the minvid can be found
+            n = 0'u8 # number of already-processed keys, for the progress bar
+
+          # The O(n^2) sort/search here is fine given the small size of the list
+          for nibble, keyvtx in keyvtxs.mpairs:
+            let subvid = vtx.bVid(uint8 nibble)
+            if (not subvid.isValid) or keyvtx[0][0].isValid:
+              n += 1 # no need to compute key
+              continue
+
+            let childVid = keyvtx[0][1].childVid
+            if not childVid.isValid:
+              # leaf vertex without storage ID - we can compute the key trivially
+              (keyvtx[0][0], keyvtx[1]) =
                 ?db.computeKeyImpl(
                   (rvid.root, subvid),
                   batch,
-                  (keyvtxs[n][0][1], keyvtxs[n][1]),
+                  keyvtx[0][1],
+                  keyvtx[1],
                   skipLayers = skipLayers,
                 )
-            batch.leave(n)
+              n += 1
+              continue
 
-            level = maxLevel(level, bl)
+            if minIdx == keyvtxs.len + 1 or childVid < minVid:
-            bkey
+              minIdx = nibble
+              minVid = childVid
+
+          if minIdx == keyvtxs.len + 1: # no uncomputed key found!
+            break keysComputed
+
+          batch.enter(n)
+          (keyvtxs[minIdx][0][0], keyvtxs[minIdx][1]) =
+            ?db.computeKeyImpl(
+              (rvid.root, vtx.bVid(uint8 minIdx)),
+              batch,
+              keyvtxs[minIdx][0][1],
+              keyvtxs[minIdx][1],
+              skipLayers = skipLayers,
+            )
+          batch.leave(n)
+
+      template writeBranch(w: var RlpWriter): HashKey =
+        w.encodeBranch(vtx):
+          if subvid.isValid:
+            level = maxLevel(level, keyvtxs[n][1])
+            keyvtxs[n][0][0]
           else:
             VOID_HASH_KEY
 
@@ -237,7 +289,7 @@ proc computeKeyImpl(
     return ok(keyvtx[0])
 
   var batch: WriteBatch
-  let res = computeKeyImpl(db, rvid, batch, (keyvtx[1], level), skipLayers = skipLayers)
+  let res = computeKeyImpl(db, rvid, batch, keyvtx[1], level, skipLayers = skipLayers)
   if res.isOk:
     ?batch.flush(db)
 
@@ -263,6 +315,7 @@ proc computeKey*(
 proc computeKeys*(db: AristoDbRef, root: VertexID): Result[void, AristoError] =
   ## Ensure that key cache is topped up with the latest state root
   discard db.computeKeyImpl((root, root), skipLayers = true)
+
   ok()
 
 # ------------------------------------------------------------------------------

nimbus/db/aristo/aristo_layers.nim

@@ -69,11 +69,6 @@ func layersGetVtx*(db: AristoDbRef; rvid: RootedVertexID): Opt[(VertexRef, int)]
 
   Opt.none((VertexRef, int))
 
-func layersGetVtxOrVoid*(db: AristoDbRef; rvid: RootedVertexID): VertexRef =
-  ## Simplified version of `layersGetVtx()`
-  db.layersGetVtx(rvid).valueOr((VertexRef(nil), 0))[0]
-
-
 func layersGetKey*(db: AristoDbRef; rvid: RootedVertexID): Opt[(HashKey, int)] =
   ## Find a hash key on the cache layers. An `ok()` result might contain a void
   ## hash key if it is stored on the cache that way.