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Shards

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Sharding is a mechanism in TON blockchain which allows to process a large number of transactions. The main idea of sharding in TON is that when account A sends a message to account B and account C sends a message to account D both of these operations can be performed asynchronously.

By default in the Basechain (workchain=0) there is only one shard with a shard number 0x8000000000000000 (or 1000000000000000000000000000000000000000000000000000000000000000 in binary representation). The masterchain (workchain=-1) always has one and only one shard.

Splitting​

Each shard is responsible for some subset of accounts with some common binary prefix. This prefix appears in shard id which presented by a 64-bit integer and has the following structure: <binary prefix>100000.... For example, shard with id 1011100000... contains all accounts started with prefix 1011.

When number of transactions in some shard growth, it splits into two shards. New shards obtaining the following ids: <parent prefix>01000... and <parent prefix>11000... and responsible for accounts starting with <parent prefix>0 and <parent prefix>1 correspondingly. The seqnos of blocks in shards goes continuously starting from parent last seqno plus 1. After split shards go independently and may have different seqnos.

Masterchain block contains information about shards in its header. After the block of shard appears in masterchain header it may be considered as finished (it cannot be rolled back).

Example:

  • Masterchain block seqno=34607821 has 2 shards: (0,4000000000000000,40485798) and (0,c000000000000000,40485843) (https://toncenter.com/api/v2/shards?seqno=34607821).
  • Shard shard=4000000000000000 was splitted into shard=2000000000000000 and shard=6000000000000000 and masterchain block seqno=34607822 already has 3 shards: (0,2000000000000000,40485799) and (0,6000000000000000,40485799). Note, that both new shards has the same seqnos but different shard IDs (https://toncenter.com/api/v2/shards?seqno=34607822).
  • New shards go independently and after 100 masterchain blocks (in masterchain block seqno=34607921) one shard has last block (0,2000000000000000,40485901) and another one has (0,6000000000000000,40485897) (https://toncenter.com/api/v2/shards?seqno=34607921).

Merging​

When shards load goes down they can merge back as follow:

  • Two shards can merge if they have common parent and, therefore, their shard ids are <parent prefix>010... and <parent prefix110.... Merged shard will have shard id <parent prefix>10... (for example 10010... + 10110... = 1010...). The first block of merged shard will have seqno=max(seqno1, seqno2) + 1.

Example: