I use ZODB and i want to copy my 'database_1.fs' file to another 'database_2.fs', so I opened the root dictionary of that 'database_1.fs' and I (pickle.dump) it in a text file.

Then I (pickle.load) it in a dictionary-variable, in the end I update the root dictionary of the other 'database_2.fs' with the dictionary-variable.

It works, but I wonder why the size of the 'database_1.fs' not equal to the size of the other 'database_2.fs'.

They are still copies of each other.

def openstorage(store):             #opens the database
    data={}
    data['file']=filestorage
    data['db']=DB(data['file'])
    data['conn']=data['db'].open()
    data['root']=data['conn'].root()
    return data

def getroot(dicty):
    return dicty['root']

def closestorage(dicty):              #close the database after Saving
    transaction.commit()
    dicty['file'].close()
    dicty['db'].close()
    dicty['conn'].close()
    transaction.get().abort()

then that's what i do:-

import pickle

loc1='G:\\database_1.fs'
op1=openstorage(loc1)
root1=getroot(op1)

loc2='G:database_2.fs'
op2=openstorage(loc2)
root2=getroot(op2)

>>> len(root1)
215
>>> len(root2)
0

pickle.dump( root1, open( "save.txt", "wb" ))
item=pickle.load( open( "save.txt", "rb" ) )          #now item is a dictionary

root2.update(item)

closestorage(op1)
closestorage(op2)

#after I open both of the databases
#I get the same keys in both databases
#But `database_2.fs`  is smaller that `database_2.fs` in size I mean.

>>> len(root2)==len(root1)==215      #they have the same keys 
True

Note:

(1) there are persistent dictionaries and lists in the original database_1.fs

(2) both of them have the same length and the same indexes.