fix: Avoid collecting unnecessary snapshots

When the logs are collected in relaxed mode it does not need to compute
the current snapshot for every single entry.

This fix speeds up large registers by ~2x.

Signed-off-by: Arnau Siches <arnau.siches@digital.cabinet-office.gov.uk>

Author: Arnau Siches

registers/log.py

@@ -175,6 +175,9 @@ def slice(log: Log, start_position: int) -> List[Command]:
     return commands
 
 
+Result = Tuple[Optional[Entry], Optional[ValidationError]]
+
+
 def _collect_command(command: Command,
                      data: Log,
                      metadata: Log,
@@ -198,26 +201,24 @@ def _collect_command(command: Command,
             raise OrphanEntry(entry)
 
         if entry.scope == Scope.System:
-            metadata.insert(blob)
-            record = metadata.snapshot().get(entry.key)
-            (_, err) = _collect_entry(entry, record)
-
-            if err and not relaxed:
-                errors.append(err)
-            else:
-                metadata.insert(entry)
+            _collect_pair(entry, blob, metadata, errors, relaxed)
+
         else:
-            data.insert(blob)
-            record = data.snapshot().get(entry.key)
-            (_, err) = _collect_entry(entry, record)
+            _collect_pair(entry, blob, data, errors, relaxed)
 
-            if err and not relaxed:
-                errors.append(err)
-            else:
-                data.insert(entry)
 
+def _collect_pair(entry: Entry, blob: Blob, log: Log,
+                  errors: List[ValidationError], relaxed: bool):
+    log.insert(blob)
 
-Result = Tuple[Optional[Entry], Optional[ValidationError]]
+    if not relaxed:
+        record = log.snapshot().get(entry.key)
+        (_, err) = _collect_entry(entry, record)
+
+        if err:
+            errors.append(err)
+
+    log.insert(entry)
 
 
 def _collect_entry(entry: Entry, record: Optional[Record]) -> Result: