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I've been studying Blockchain since a while and I've been looking out for information explaining where the blockchain ledger is saved and how it is saved locally (as in, locally in a full node). What I have most of the time found is state database being used by Ethereum or Hyperledger Fabric using LevelDB or RocksDB e.t.c for saving state information. I've been struggling real hard to know where the blockchain ledger gets saved apart from states being saved in some on-disk key-value store/database as I am studying LinkedList and Merkle Tree (Hash Tree) which are being used to store new blocks that gets created and being hashed and saved in merkle tree for verification purpose by full nodes and half nodes can query & verify if transactions exist.

Thanks and best,

Rohit

rohitpaniker
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2 Answers2

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In Bitcoin-core, the blocks are stored in .dat files in the blocks filder under the data directory (default on linux is ~/.bitcoin). These files are not necessarily numbered or organized in any strict fashion, because they are downloaded as available, instead of waiting for each sequential block to become available for download from a peer. For those reasons, the .dat files There is a levelDB (in ~/.bitcoin/blocks/index) which indexes the blockchain by storing the names and locations of the .dat files.

Linked lists and merkle trees are not data storage mechanisms, but abstract data types, which can exist in a database, as flat files, etc. A merkle tree can make validation much faster because it improves the efficiency of the verification algorithms, usually a hash function.

JBaczuk
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  • Oh okay so if there are 100 transactions then there would be 100 .dat files, one .dat file per transaction and each transaction is being stored in LevelDB ? – rohitpaniker Nov 21 '18 at 11:22
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    Not quite, one.dat file can contain multiple blocks, which each contains many transactions. LevelDB contains references to the files. – JBaczuk Nov 21 '18 at 12:17
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In Hyperledger Fabric, the state database is not for storing all the blocks, it saves the current state of an asset only e.g. if a bank account has a transaction of 10 debit and another transaction of 2 credit, the state DB will have the current value of 8.

The actual blocks are saved in in a local file in peers, which can be queried via the SDK.

adnan.c
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