neo-go/docs/neofs-blockstorage.md

NeoFS block storage

Using NeoFS to store chain's blocks and snapshots was proposed in #3463. NeoGo contains several extensions utilizing NeoFS block storage aimed to improve node synchronization efficiency and reduce node storage size.

Components and functionality

Block storage schema

A single NeoFS container is used to store blocks and index files. Each block is stored in a binary form as a separate object with a unique OID and a set of attributes:

• block object identifier with block index value (block:1)
• primary node index (primary:0)
• block hash in the LE form (hash:5412a781caf278c0736556c0e544c7cfdbb6e3c62ae221ef53646be89364566b)
• previous block hash in the LE form (prevHash:3654a054d82a8178c7dfacecc2c57282e23468a42ee407f14506368afe22d929)
• millisecond-precision block timestamp (time:1627894840919)

Each index file is an object containing a constant-sized batch of raw block object IDs in binary form ordered by block index. Each index file is marked with the following attributes:

• index file identifier with consecutive file index value (oid:0)
• the number of OIDs included into index file (size:128000)

NeoFS BlockFetcher

NeoFS BlockFetcher service is designed as an alternative to P2P synchronisation protocol. It allows to download blocks from a trusted container in the NeoFS network and persist them to database using standard verification flow. NeoFS BlockFetcher service primarily used during the node's bootstrap, providing a fast alternative to P2P blocks synchronisation.

NeoFS BlockFetcher service has two modes of operation:

• Index File Search: Search for index files, which contain batches of block object IDs and fetch blocks from NeoFS by retrieved OIDs.
• Direct Block Search: Search and fetch blocks directly from NeoFS container via built-in NeoFS object search mechanism.

Operation mode of BlockFetcher can be configured via SkipIndexFilesSearch parameter.

Operation flow

1. OID Fetching: Depending on the mode, the service either:

   • Searches for index files by index file attribute and reads block OIDs from index file object-by-object.
   • Searches batches of blocks directly by block attribute (the batch size is configured via OIDBatchSize parameter).

   Once the OIDs are retrieved, they are immediately redirected to the block downloading routines for further processing. The channel that is used to redirect block OIDs to downloading routines is buffered to provide smooth OIDs delivery without delays. The size of this channel can be configured via OIDBatchSize parameter and equals to 2*OIDBatchSize.

2. Parallel Block Downloading: The number of downloading routines can be configured via DownloaderWorkersCount parameter. It's up to the user to find the balance between the downloading speed and blocks persist speed for every node that uses NeoFS BlockFetcher. Downloaded blocks are placed into a buffered channel of size IDBatchSize with further redirection to the block queue.

3. Block Insertion: Downloaded blocks are inserted into the blockchain using the same logic as in the P2P synchronisation protocol. The block queue is used to order downloaded blocks before they are inserted into the blockchain. The size of the queue can be configured via the BQueueSize parameter and should be larger than the OIDBatchSize parameter to avoid blocking the downloading routines.

Once all blocks available in the NeoFS container are processed, the service shuts down automatically.