# Local chain storage (database)¶

Every valid block proposal created is saved locally on the device. Additionally, all of the incoming blocks of other peers, either as a response to a crawlrequest or in other ways, are saved locally when validated correctly. The blocks are saved using an SQLite database. Android has code in place to handle all the complicated parts, so using the database after setup consists mainly of writing queries. Please refer to the Android tutorials for an explanation on how to use SQLite databases in Android.

The database is set up in a similar way as in the ipv8 python code. The only difference is the added column TX_FORMAT. So the database from the ipv8 implementation in python can be imported trivially into android. The columns correspond to the Message structure (Protocolbuffers), so for inserting it simply needs to parse relevant data from the block. Note that it when receiving raw bytes it always has to be passed to a Protocol Buffers object first before it is added to the database, to ensure that data was received correctly.

## Database structure¶

The table has the following columns:

• TX - Transaction
• TX_FORMAT - Transaction format e.g. pdf
• PUBLIC_KEY - Base64 encoding of the raw public key pair bytes (see Crypto)
• SEQUENCE_NUMBER - sequence number of the block
• LINK_PUBLIC_KEY - Base64 encoding of the public key pair of the linked block
• LINK_SEQUENCE_NUMBER - sequence number of the linked block
• PREVIOUS_HASH - Base64 encoding of the hash of the previous block in the chain
• SIGNATURE - Base64 encoding of the signature
• INSERT_TIME - Time at which the block was inserted into the database
• BLOCK_HASH - Base64 encoding of the hash

The primary keys are the public key and the sequence number.