Add a example on how to grab the aggregate size on disk or memory for a branch

(cherry picked from v5-34-00-patches
 commit b91fea57)

tutorials/tree/printSizes.C

+#include "TTree.h"
+#include "TBranch.h"
+#include "Riostream.h"
+#include "TMemFile.h"
+#include "TKey.h"
+#include "TBranchRef.h"
+ 
+//
+// This macro can be used to get aggregate information on the size
+// take on disk or in memory by the various branches in a TTree.
+// For example:
+/*
+
+root [] printTreeSummary(tree);
+The TTree "T" takes 3764343 bytes on disk
+  It's branch "event" takes 3760313 bytes on disk
+
+root [] printBranchSummary(tree->GetBranch("event"));
+The branch "event" takes 3760313 bytes on disk
+  It's sub-branch "TObject" takes 581 bytes on disk
+  It's sub-branch "fType[20]" takes 640 bytes on disk
+  It's sub-branch "fEventName" takes 855 bytes on disk
+  It's sub-branch "fNtrack" takes 506 bytes on disk
+  It's sub-branch "fNseg" takes 554 bytes on disk
+  It's sub-branch "fNvertex" takes 507 bytes on disk
+  It's sub-branch "fFlag" takes 420 bytes on disk
+  It's sub-branch "fTemperature" takes 738 bytes on disk
+  It's sub-branch "fMeasures[10]" takes 1856 bytes on disk
+  It's sub-branch "fMatrix[4][4]" takes 4563 bytes on disk
+  It's sub-branch "fClosestDistance" takes 2881 bytes on disk
+  It's sub-branch "fEvtHdr" takes 847 bytes on disk
+  It's sub-branch "fTracks" takes 3673982 bytes on disk
+  It's sub-branch "fHighPt" takes 59640 bytes on disk
+  It's sub-branch "fMuons" takes 1656 bytes on disk
+  It's sub-branch "fLastTrack" takes 785 bytes on disk
+  It's sub-branch "fWebHistogram" takes 596 bytes on disk
+  It's sub-branch "fH" takes 10076 bytes on disk
+  It's sub-branch "fTriggerBits" takes 1699 bytes on disk
+  It's sub-branch "fIsValid" takes 366 bytes on disk
+
+ */
+
+Long64_t GetTotalSize(TBranch * b, bool ondisk, bool inclusive);
+Long64_t GetBasketSize(TBranch * b, bool ondisk, bool inclusive);
+
+Long64_t GetBasketSize(TObjArray * branches, bool ondisk, bool inclusive) {
+   Long64_t result = 0;
+   size_t n = branches->GetEntries();
+   for( size_t i = 0; i < n; ++ i ) {
+      result += GetBasketSize( dynamic_cast<TBranch*>( branches->At( i ) ), ondisk, inclusive );
+   }
+   return result;
+}
+
+Long64_t GetBasketSize(TBranch * b, bool ondisk, bool inclusive) {
+   Long64_t result = 0;
+   if (b) {
+      if (ondisk && b->GetZipBytes() > 0) {
+         result = b->GetZipBytes();
+      } else {
+         result = b->GetTotBytes();
+      }
+      if (inclusive) {
+         result += GetBasketSize(b->GetListOfBranches(), ondisk, true);
+      }
+      return result;
+   }
+   return result;
+}
+
+Long64_t GetTotalSize( TBranch * br, bool ondisk, bool inclusive ) {
+   TMemFile f("buffer","CREATE");
+   if (br->GetTree()->GetCurrentFile()) {
+      f.SetCompressionSettings(br->GetTree()->GetCurrentFile()->GetCompressionSettings());
+   }
+   f.WriteObject(br,"thisbranch");
+   TKey* key = f.GetKey("thisbranch");
+   Long64_t size;
+   if (ondisk) 
+      size = key->GetNbytes();
+   else 
+      size = key->GetObjlen();      
+   return GetBasketSize(br, ondisk, inclusive) + size;
+}
+
+Long64_t GetTotalSize( TObjArray * branches, bool ondisk ) {
+   Long64_t result = 0;
+   size_t n = branches->GetEntries();
+   for( size_t i = 0; i < n; ++ i ) {
+      result += GetTotalSize( dynamic_cast<TBranch*>( branches->At( i ) ), ondisk, true );
+      cerr << "After " << branches->At( i )->GetName() << " " << result << endl;
+   }
+   return result;
+}
+
+Long64_t GetTotalSize(TTree *t, bool ondisk) {
+   TKey *key = 0;
+   if (t->GetDirectory()) {
+      key = t->GetDirectory()->GetKey(t->GetName());
+   }
+   Long64_t ondiskSize = 0;
+   Long64_t totalSize = 0;
+   if (key) {
+      ondiskSize = key->GetNbytes();
+      totalSize = key->GetObjlen();
+   } else {
+      TMemFile f("buffer","CREATE");
+      if (t->GetCurrentFile()) {
+         f.SetCompressionSettings(t->GetCurrentFile()->GetCompressionSettings());
+      }
+      f.WriteTObject(t);
+      key = f.GetKey(t->GetName());
+      ondiskSize = key->GetNbytes();
+      totalSize = key->GetObjlen();      
+   }
+   if (t->GetBranchRef() ) {
+      if (ondisk) {
+         ondiskSize += GetBasketSize(t->GetBranchRef(), true, true);
+      } else {
+         totalSize += GetBasketSize(t->GetBranchRef(), false, true);
+      }
+   }
+   if (ondisk) {      
+      return ondiskSize + GetBasketSize(t->GetListOfBranches(), /* ondisk */ true, /* inclusive */ true);
+   } else {
+      return totalSize + GetBasketSize(t->GetListOfBranches(), /* ondisk */ false, /* inclusive */ true);
+   }
+}
+
+Long64_t sizeOnDisk(TTree *t) { 
+   // Return the size on disk on this TTree.
+   
+   return GetTotalSize(t, true);
+}
+
+Long64_t sizeOnDisk(TBranch *branch, bool inclusive) 
+{
+   // Return the size on disk on this branch.
+   // If 'inclusive' is true, include also the size
+   // of all its sub-branches.
+
+   return GetTotalSize(branch, true, inclusive);
+}
+
+void printBranchSummary(TBranch *br)
+{
+   cout << "The branch \"" << br->GetName() << "\" takes " << sizeOnDisk(br,true) << " bytes on disk\n";
+   size_t n = br->GetListOfBranches()->GetEntries();
+   for( size_t i = 0; i < n; ++ i ) {
+      TBranch *subbr = dynamic_cast<TBranch*>(br->GetListOfBranches()->At(i));
+      cout << "  It's sub-branch \"" << subbr->GetName() << "\" takes " << sizeOnDisk(subbr,true) << " bytes on disk\n";
+   }   
+}
+
+void printTreeSummary(TTree *t)
+{
+   cout << "The TTree \"" << t->GetName() << "\" takes " << sizeOnDisk(t) << " bytes on disk\n";
+   size_t n = t->GetListOfBranches()->GetEntries();
+   for( size_t i = 0; i < n; ++ i ) {
+      TBranch *br =dynamic_cast<TBranch*>(t->GetListOfBranches()->At(i));
+      cout << "  It's branch \"" << br->GetName() << "\" takes " << sizeOnDisk(br,true) << " bytes on disk\n";
+   }
+}