[ROOT] Problem with Automatic schema evolution?

From: Ruben Shahoyan (Ruben.Shahoyan@cern.ch)
Date: Wed Mar 24 2004 - 17:40:15 MET


Hello,
we have a following problem with I/O of the objects having streamer 
versions:
the base object for na60 digits is

class NaDigit1D : 
public TObject { 
...
 protected:
  Int_t fI;             // Value of the digit
  Int_t fCluster;       // Number of the Cluster to which it is attached
  TArrayI* fTracks;     // Optional array of references on track
  //
#ifdef STOREFULLINFO
  Float_t fXYZE[4];
  ClassDef(NaDigit1D,2) // Base class for 1Dim digits with FULL TRACKING INFO
#else
  ClassDef(NaDigit1D,1) // Base class for 1Dim digits
#endif
};

the #define STOREFULLINFO in the NaDigit1D.h allows us to switch from 
version 1 to more complete version 2.

The default constructor is:
NaDigit1D::NaDigit1D()
{ 
  fI = -1;
  fCluster = -1;
  fTracks = 0; 
#ifdef STOREFULLINFO
  fXYZE[0]=fXYZE[1]=fXYZE[2]=fXYZE[3]=0.0;
#endif
  //
}

The I/O works fine when I read/rewrite the digits of some version with the 
code compiled with the corresponding version of the class.

But we have large amount of data written with the version 1 (i.e. w/o 
fXYZE member) which we need to read and store after some processing as a 
digits of version 2 (with fXYZE member). The code compiled with 
#define STOREFULLINFO reads w/o problem the old digits of version 1,
but when I sotre them again, and try to read them back as a digits of 
version 2, they appear to be completely corrupted.

Here is what I get with gDebug = 1 for reading of the class NaPixDigit, 
which derives from NaDigit1D by adding a new member fCol.

(1) Reading the NaDigit1D of version 1 with the class compiled for version 2
...
====>Rebuilding TStreamerInfo for class: NaPixDigit, version: 1
====>Rebuilding TStreamerInfo for class: NaDigit1D, version: 1
StreamerInfo for class: NaDigit1D, version=1
  TObject       BASE            offset=  0 type=66 Basic ROOT object   
  Int_t         fI              offset= 12 type= 3 Value of the digit  
  Int_t         fCluster        offset= 16 type= 3 Number of the Cluster to which it is attached
  TArrayI*      fTracks         offset= 20 type=69 Optional array of references on track
   i= 0, TObject         type= 66, offset=  0, len=1, method=0
   i= 1, fI              type=  3, offset= 12, len=1, method=0
   i= 2, fCluster        type=  3, offset= 16, len=1, method=0
   i= 3, fTracks         type= 69, offset= 20, len=1, method=1074526452

StreamerInfo for class: NaPixDigit, version=1
  NaDigit1D     BASE            offset=  0 type= 0 Base class for 1Dim digits
  Int_t         fCol            offset= 40 type= 3 Column of the pixel (NaDigit1D::fI is row)
   i= 0, NaDigit1D       type=  0, offset=  0, len=1, method=161037840
   i= 1, fCol            type=  3, offset= 40, len=1, method=0

....
root [10] gVerTel->GetSensor(0)->GetDigit(2)->Dump()
==>Dumping object at:a273f80, name=NaPixDigit, class=NaPixDigit
fCol                          0           Column of the pixel (NaDigit1D::fI is row)
fI                            147         Value of the digit
fCluster                      2           Number of the Cluster to which it is attached
*fTracks                      ->0         Optional array of references on track
fXYZE[4]                      0           
fUniqueID                     131185      object unique identifier
fBits                         50331648    bit field status word

Here everything is correct. Now I store these digits and try to 
(2) read them back with the same code of NaDigit1D version 2:


====>Rebuilding TStreamerInfo for class: NaPixDigit, version: 1
Creating StreamerInfo for class: NaDigit1D, version: 2

StreamerInfo for class: NaDigit1D, version=2
  TObject       BASE            offset=  0 type=66 Basic ROOT object   
  Int_t         fI              offset= 12 type= 3 Value of the digit  
  Int_t         fCluster        offset= 16 type= 3 Number of the Cluster to which it is attached
  TArrayI*      fTracks         offset= 20 type=69 Optional array of references on track
  Float_t       fXYZE[4]        offset= 24 type=25                     
   i= 0, TObject         type= 66, offset=  0, len=1, method=0
   i= 1, fI              type= 23, offset= 12, len=2, method=0
   i= 2, fTracks         type= 69, offset= 20, len=1, method=1074526452
   i= 3, fXYZE           type= 25, offset= 24, len=4, method=0

StreamerInfo for class: NaPixDigit, version=1
  NaDigit1D     BASE            offset=  0 type= 0 Base class for 1Dim digits
  Int_t         fCol            offset= 40 type= 3 Column of the pixel (NaDigit1D::fI is row)
   i= 0, NaDigit1D       type=  0, offset=  0, len=1, method=160981416
   i= 1, fCol            type=  3, offset= 40, len=1, method=0

...
root [9] gVerTel->GetSensor(0)->GetDigit(2)->Dump()
==>Dumping object at:a5c2f38, name=NaPixDigit, class=NaPixDigit

fCol                          0           Column of the pixel (NaDigit1D::fI is row)
fI                            178         Value of the digit
fCluster                      185         Number of the Cluster to which it is attached
*fTracks                      ->0         Optional array of references on track
fXYZE[4]                      0           
fUniqueID                     131185      object unique identifier
fBits                         50331648    bit field status word

The same digit now has completely different values, and the StreamerInfo 
also looks different: in the output (1) it had a table entry for
i= 2, fCluster        type=  3, offset= 16, len=1, method=0

while in the output (2) it has disappeared, which apparently leads to 
misalignment during the reading.

Have I done something wrong or there is a problem in the schema evolution?

Ruben Shahoyan



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