Add a comment the isAvailable() function is potentially costly

DataFormats/Common/interface/Ptr.h

@@ -149,6 +149,8 @@ namespace edm {
 
     /// Checks if collection is in memory or available
     /// in the event. No type checking is done.
+    /// This function is potentially costly as it might cause a disk
+    /// read (note that it does not cause the data to be cached locally)
     bool isAvailable() const;
 
     /// Checks if this Ptr is transient (i.e. not persistable).

DataFormats/Common/interface/Ref.h

@@ -257,6 +257,8 @@ namespace edm {
 
     /// Checks if collection is in memory or available
     /// in the Event. No type checking is done.
+    /// This function is potentially costly as it might cause a disk
+    /// read (note that it does not cause the data to be cached locally)
     bool isAvailable() const;
 
     /// Checks if this ref is transient (i.e. not persistable).
@@ -404,6 +406,8 @@ namespace edm {
 
     /// Checks if collection is in memory or available
     /// in the Event. No type checking is done.
+    /// This function is potentially costly as it might cause a disk
+    /// read (note that it does not cause the data to be cached locally)
     bool isAvailable() const;
 
     /// Checks if this ref is transient (i.e. not persistable).

DataFormats/Common/interface/RefCoreWithIndex.h

@@ -88,7 +88,8 @@ namespace edm {
 
     // Checks if collection is in memory or available
     // in the Event. No type checking is done.
-
+    // This function is potentially costly as it might cause a disk
+    // read (note that it does not cause the data to be cached locally)
     bool isAvailable() const { return toRefCore().isAvailable(); }
 
     //Convert to an equivalent RefCore. Needed for Ref specialization.

DataFormats/Common/interface/RefProd.h

@@ -134,6 +134,8 @@ namespace edm {
 
     /// Checks if collection is in memory or available
     /// in the Event. No type checking is done.
+    /// This function is potentially costly as it might cause a disk
+    /// read (note that it does not cause the data to be cached locally)
     bool isAvailable() const { return product_.isAvailable(); }
 
     /// Checks if this RefProd is transient (i.e. not persistable).

DataFormats/Common/interface/RefToBase.h

@@ -116,6 +116,8 @@ namespace edm {
 
     /// Checks if collection is in memory or available
     /// in the Event. No type checking is done.
+    /// This function is potentially costly as it might cause a disk
+    /// read (note that it does not cause the data to be cached locally)
     bool isAvailable() const { return holder_ ? holder_->isAvailable() : false; }
 
     bool isTransient() const { return holder_ ? holder_->isTransient() : false; }

DataFormats/Common/interface/RefToBaseProd.h

@@ -68,6 +68,8 @@ namespace edm {
 
     /// Checks if collection is in memory or available
     /// in the Event. No type checking is done.
+    /// This function is potentially costly as it might cause a disk
+    /// read (note that it does not cause the data to be cached locally)
     bool isAvailable() const { return product_.isAvailable(); }
 
     /// Checks for null