Implement snapshots cache in aristo database

execution_chain/db/aristo/aristo_desc.nim

@@ -22,7 +22,7 @@
 {.push raises: [].}
 
 import
-  std/[hashes, sequtils, sets, tables],
+  std/[hashes, sequtils, sets, tables, heapqueue],
   eth/common/hashes, eth/trie/nibbles,
   results,
   ./aristo_constants,
@@ -34,7 +34,7 @@ import
 # Not auto-exporting backend
 export
   tables, aristo_constants, desc_error, desc_identifiers, nibbles,
-  desc_structural, minilru, hashes, PutHdlRef
+  desc_structural, minilru, hashes, heapqueue, PutHdlRef
 
 type
   AristoTxRef* = ref object
@@ -124,6 +124,17 @@ type
       ## MPT level where "most" leaves can be found, for static vid lookups
     lookups*: tuple[lower, hits, higher: int]
 
+    snapshots*: HeapQueue[AristoTxRef]
+      ## A priority queue of txFrames holding snapshots. Used to limit the number
+      ## of snapshots that can be taken and therefore limit memory usage and also
+      ## to support cleaning old values out of snapshots after persisting to the
+      ## database. txFrames in the queue are sorted by their level in ascending order.
+
+    maxSnapshots*: int
+      ## The maximum number of snapshots to hold in the snapshots queue. When the queue
+      ## is full (queue.len == maxSnapshots) then the oldest snapshot is removed from
+      ## the queue and cleaned up.
+
   Leg* = object
     ## For constructing a `VertexPath`
     wp*: VidVtxPair                ## Vertex ID and data ref
@@ -139,9 +150,7 @@ const
   dbLevel* = -1
   disposedLevel* = int.low
 
-# ------------------------------------------------------------------------------
-# Public helpers
-# ------------------------------------------------------------------------------
+proc `<`*(a, b: AristoTxRef): bool = a.level < b.level
 
 template mixUp*(accPath, stoPath: Hash32): Hash32 =
   # Insecure but fast way of mixing the values of two hashes, for the purpose
@@ -170,8 +179,6 @@ func getOrVoid*[W](tab: Table[W,RootedVertexID]; w: W): RootedVertexID =
 func getOrVoid*[W](tab: Table[W,HashSet[RootedVertexID]]; w: W): HashSet[RootedVertexID] =
   tab.getOrDefault(w, default(HashSet[RootedVertexID]))
 
-# --------
-
 func isValid*(vtx: VertexRef): bool =
   not isNil(vtx)
 
@@ -197,20 +204,12 @@ func isValid*(rvid: RootedVertexID): bool =
 func isValid*(sqv: HashSet[RootedVertexID]): bool =
   sqv.len > 0
 
-# ------------------------------------------------------------------------------
-# Public functions, miscellaneous
-# ------------------------------------------------------------------------------
-
 func hash*(db: AristoDbRef): Hash {.error.}
 func hash*(db: AristoTxRef): Hash {.error.}
 
 proc baseTxFrame*(db: AristoDbRef): AristoTxRef =
   db.txRef
 
-# ------------------------------------------------------------------------------
-# Public helpers
-# ------------------------------------------------------------------------------
-
 iterator rstack*(tx: AristoTxRef, stopAtSnapshot = false): AristoTxRef =
   # Stack in reverse order, ie going from tx to base
   var tx = tx
@@ -254,8 +253,3 @@ func getStaticLevel*(db: AristoDbRef): int =
     db.staticLevel = 1
 
   db.staticLevel
-
-
-# ------------------------------------------------------------------------------
-# End
-# ------------------------------------------------------------------------------

execution_chain/db/aristo/aristo_init/init_common.nim

@@ -86,6 +86,7 @@ proc initInstance*(db: AristoDbRef): Result[void, AristoError] =
   db.txRef = AristoTxRef(db: db, vTop: vTop, snapshot: Snapshot(level: Opt.some(0)))
   db.accLeaves = LruCache[Hash32, AccLeafRef].init(ACC_LRU_SIZE)
   db.stoLeaves = LruCache[Hash32, StoLeafRef].init(ACC_LRU_SIZE)
+  db.maxSnapshots = 10
   ok()
 
 proc finish*(db: AristoDbRef; eradicate = false) =

execution_chain/db/aristo/aristo_tx_frame.nim

@@ -25,6 +25,44 @@ template isDisposed(txFrame: AristoTxRef): bool =
 proc isKeyframe(txFrame: AristoTxRef): bool =
   txFrame == txFrame.db.txRef
 
+proc clearSnapshot*(txFrame: AristoTxRef) {.raises: [], gcsafe.}
+
+proc removeSnapshotFrame(db: AristoDbRef, txFrame: AristoTxRef) =
+  let index = db.snapshots.find(txFrame)
+  if index != -1:
+    db.snapshots.del(index)
+
+proc addSnapshotFrame(db: AristoDbRef, txFrame: AristoTxRef) =
+  doAssert txFrame.snapshot.level.isSome()
+
+  if db.snapshots.len() == db.maxSnapshots:
+    let frame = db.snapshots.pop()
+    frame.clearSnapshot()
+
+  db.snapshots.push(txFrame)
+
+proc cleanSnapshots(db: AristoDbRef) =
+  let minLevel = db.txRef.level
+
+  # Some of the snapshot content may have already been persisted to disk
+  # (since they were made based on the in-memory frames at the time of creation).
+  # Annoyingly, there's no way to remove items while iterating but even
+  # with the extra seq, move + remove turns out to be faster than
+  # creating a new table - specially when the ratio between old and
+  # and current items favors current items.
+  template delIfIt(tbl: var Table, body: untyped) =
+    var toRemove = newSeqOfCap[typeof(tbl).A](tbl.len div 2)
+    for k, it {.inject.} in tbl:
+      if body:
+        toRemove.add k
+    for k in toRemove:
+      tbl.del(k)
+
+  for frame in db.snapshots:
+    frame.snapshot.vtx.delIfIt(it[2] < minLevel)
+    frame.snapshot.acc.delIfIt(it[1] < minLevel)
+    frame.snapshot.sto.delIfIt(it[1] < minLevel)
+
 proc buildSnapshot(txFrame: AristoTxRef, minLevel: int) =
   # Starting from the previous snapshot, build a snapshot that includes all
   # ancestor changes as well as the changes in txFrame itself
@@ -41,30 +79,11 @@ proc buildSnapshot(txFrame: AristoTxRef, minLevel: int) =
       if frame.snapshot.level.isSome() and not isKeyframe:
         # `frame` has a snapshot only in the first iteration of the for loop
         txFrame.snapshot = move(frame.snapshot)
+        txFrame.db.removeSnapshotFrame(frame)
 
         # Verify that https://github.com/nim-lang/Nim/issues/23759 is not present
         assert frame.snapshot.vtx.len == 0 and frame.snapshot.level.isNone()
 
-        if txFrame.snapshot.level != Opt.some(minLevel):
-          # When recycling an existing snapshot, some of its content may have
-          # already been persisted to disk (since it was made base on the
-          # in-memory frames at the time of its creation).
-          # Annoyingly, there's no way to remove items while iterating but even
-          # with the extra seq, move + remove turns out to be faster than
-          # creating a new table - specially when the ratio between old and
-          # and current items favors current items.
-          template delIfIt(tbl: var Table, body: untyped) =
-            var toRemove = newSeqOfCap[typeof(tbl).A](tbl.len div 2)
-            for k, it {.inject.} in tbl:
-              if body:
-                toRemove.add k
-            for k in toRemove:
-              tbl.del(k)
-
-          txFrame.snapshot.vtx.delIfIt(it[2] < minLevel)
-          txFrame.snapshot.acc.delIfIt(it[1] < minLevel)
-          txFrame.snapshot.sto.delIfIt(it[1] < minLevel)
-
       if frame.snapshot.level.isSome() and isKeyframe:
         txFrame.snapshot.vtx = initTable[RootedVertexID, VtxSnapshot](
           max(1024, max(frame.sTab.len, frame.snapshot.vtx.len))
@@ -96,6 +115,9 @@ proc buildSnapshot(txFrame: AristoTxRef, minLevel: int) =
 
   txFrame.snapshot.level = Opt.some(minLevel)
 
+  if not txFrame.isKeyframe():
+    txFrame.db.addSnapshotFrame(txFrame)
+
 # ------------------------------------------------------------------------------
 # Public functions
 # ------------------------------------------------------------------------------
@@ -115,6 +137,8 @@ proc txFrameBegin*(
     level: parent.level + 1)
 
 proc dispose*(txFrame: AristoTxRef) =
+  if not txFrame.db.isNil():
+    txFrame.db.removeSnapshotFrame(txFrame)
   txFrame[].reset()
   txFrame.level = disposedLevel
 
@@ -246,6 +270,11 @@ proc persist*(db: AristoDbRef, batch: PutHdlRef, txFrame: AristoTxRef) =
     else:
       discard db.stoLeaves.update(mixPath, vtx)
 
+  # Remove snapshot data that has been persisted to disk to save memory.
+  # All snapshot records with a level lower than the current base level
+  # are deleted.
+  db.cleanSnapshots()
+
   txFrame.snapshot.vtx.clear()
   txFrame.snapshot.acc.clear()
   txFrame.snapshot.sto.clear()

tests/test_aristo/test_tx_frame.nim

@@ -315,8 +315,7 @@ suite "Aristo TxFrame":
     # Verify that getting the state root of the level 3 txFrame does not impact
     # the persisted state in the database.
     let stateRootBefore = tx3.fetchStateRoot().get()
-    expect(Defect):
-      discard tx4.fetchStateRoot()
+    discard tx4.fetchStateRoot()
     let stateRootAfter = tx3.fetchStateRoot().get()
     check stateRootBefore == stateRootAfter
 
@@ -346,7 +345,7 @@ suite "Aristo TxFrame":
     for i in 1..<10:
       let acc = makeAccount(i.uint64)
       check tx1.mergeAccountRecord(acc[0], acc[1]).isOk()
-      
+
     tx1.checkpoint(1, skipSnapshot = false)
 
     let