What is the magic number for a Berkeley DB v9 Btree with a native byte order? Is there any specific length on magic numbers or any easy way to identify them?
As you've found it's 0x00053162. I'm assuming by native byte order, you mean x86 native byte order? If you hexdump the file, you'll see it in bytes 12-15, byteswapped (as 3162 0005, because it's x86):
hexdump blah.db | head -1
0000000 0001 0000 9fbc 0009 0000 0000 3162 0005
0000010 0009 0000 1000 0000 0900 0001 0000 0000
The version is in the next uint32_t, bytes 16-19. Here, it's 0009 0000, which is version 9 in little endian-speak. In fact, that whole sequence of bytes starting at offset 12 looks to be a struct __db_bt_stat, the content of which is given in the manpage for db_stat (or Db::stat) available here: http://www.mit.edu/afs.new/athena/astaff/source/src-9.0/third/db/docs/api_cxx/Db/stat.html