All binary file format in MapDB start with 32byte header. That identifies type of file, its format version and features used in

Structure

• 2 bytes - format ID, (StoreDirect, StoreWAL….)
• 2 bytes - format version,
  • number increases with backward incompatible changes (new features)
  • MapDB will refuse to open newer formats to prevent data corruption
• 4 bytes - Wide Flags; features supported by most formats
  • file wide checksum ?, type of checksum used… (CRC32,)
  • file size supported?
  • pointer checksums?
  • type of compression?
  • some basic serialization info?
  • is the space zeroed out?
• 8 bytes - file size, if set in wide feature flag
• 8 bytes - 64 bit or 32bit checksum (both will use 8 bytes)
• 8 bytes - Format Flags - features only supported by single format
  • type of pointer checksums
  • how zero space