Grib encoder should handle single metadata differently

src/earthkit/data/encoders/grib.py

@@ -723,15 +723,21 @@ def _make_message(
             else:
                 multiple[k] = v
 
-        try:
-            # Try to set all metadata at once
-            # This is needed when we set multiple keys that are interdependent
-            handle.set_multiple(single)
-        except Exception as e:
-            LOG.error("Failed to set metadata at once: %s", e)
-            # Try again, but one by one
-            for k, v in single.items():
-                handle.set(k, v)
+        if len(single) == 1:
+            # if there is only one key, set it directly to avoid the overhead of set_multiple
+            k, v = next(iter(single.items()))
+            handle.set(k, v)
+            single = {}
+        elif len(single) > 1:
+            try:
+                # Try to set all metadata at once
+                # This is needed when we set multiple keys that are interdependent
+                handle.set_multiple(single)
+            except Exception as e:
+                LOG.warning("Failed to set metadata at once: %s", e)
+                # Try again, but one by one
+                for k, v in single.items():
+                    handle.set(k, v)
 
         for k, v in multiple.items():
             handle.set(k, v)

src/earthkit/data/sources/virtual.py

@@ -14,7 +14,7 @@
 
 from earthkit.data.readers.grib.index import GribFieldList
 
-import earthkit.data as cml
+from earthkit.data import from_source
 from earthkit.data.utils.serialise import register_serialisation
 
 LOG = logging.getLogger(__name__)
@@ -60,7 +60,7 @@ def shape(self):
         return source[self.index].shape
 
 
-class DictOveray(dict):
+class DictOverlay(dict):
     def __init__(self, field):
         self.field = field
 
@@ -86,8 +86,8 @@ def __init__(self, **kwargs):
         )
         self.request.update(kwargs)
 
-        self.reference = DictOveray(
-            cml.from_source(
+        self.reference = DictOverlay(
+            from_source(
                 "cds",
                 date=19590101,
                 time=0,
@@ -140,7 +140,7 @@ def full_month(self, date):
             yyyy = yyyymm // 100
             mm = yyyymm % 100
             last = calendar.monthrange(yyyy, mm)[1]
-            source = cml.from_source(
+            source = from_source(
                 "cds",
                 year=yyyy,
                 month=mm,