plugeth-statediff/README.md

plugeth-statediff

This package provides a PluGeth plugin implementing an auxiliary service that asynchronously computes changes in the go-ethereum state trie. The service continuously listens for chain updates and builds state diffs, then relays the data to RPC subscribers or writes them directly to Postgres as IPLD objects.

It also exposes RPC endpoints for fetching or writing to Postgres the state diff at a specific block height or for a specific block hash. This operates on historical block and state data, and so depends on a complete state archive.

Data is emitted in this differential format in order to make it feasible to the entire Ethereum state and publish it to IPLD (including intermediate state and storage trie nodes). If this service is run continuously from genesis, the entire state at any block can be materialized from the cumulative differentials up to that point.

Interface types

The primary interface type is Payload, which serves as the main interface for accessing data in a service. It packages various data components such as block RLP, total difficulty, receipts RLP, and state object RLP. This encapsulates all of the differential data at a given block, and allows us to index the entire Ethereum data structure as hash-linked IPLD objects.

The StateObject type represents the final diff output structure, including an array of state leaf nodes and IPLD objects. For convenience, we also associate this object with the block number and hash.

State leaf nodes contain information about account changes, including whether they are removed, an account wrapper with account details and identifiers, and an array of storage leaf nodes representing storage changes. The IPLD type encapsulates CID-content pairs, used for code mappings and trie node (both intermediate and leaf) IPLD objects. Lastly, CodeAndCodeHash stores codehash-to-code mappings.

// Payload packages the data to send to state diff subscriptions
type Payload struct {
    BlockRlp        []byte   `json:"blockRlp"`
    TotalDifficulty *big.Int `json:"totalDifficulty"`
    ReceiptsRlp     []byte   `json:"receiptsRlp"`
    StateObjectRlp  []byte   `json:"stateObjectRlp"    gencodec:"required"`

    // ...
}

// in package "types":

// StateObject is the final output structure from the builder
type StateObject struct {
    BlockNumber *big.Int        `json:"blockNumber"     gencodec:"required"`
    BlockHash   common.Hash     `json:"blockHash"       gencodec:"required"`
    Nodes       []StateLeafNode `json:"nodes"           gencodec:"required"`
    IPLDs       []IPLD          `json:"iplds"`
}

// StateLeafNode holds the data for a single state diff leaf node
type StateLeafNode struct {
    Removed        bool
    AccountWrapper AccountWrapper
    StorageDiff    []StorageLeafNode
}

// AccountWrapper is used to temporarily associate the unpacked node with its raw values
type AccountWrapper struct {
    Account *types.StateAccount
    LeafKey []byte
    CID     string
}

// StorageLeafNode holds the data for a single storage diff node leaf node
type StorageLeafNode struct {
    Removed bool
    Value   []byte
    LeafKey []byte
    CID     string
}

// IPLD holds a cid:content pair, e.g. for codehash to code mappings or for intermediate node IPLD objects
type IPLD struct {
    CID     string
    Content []byte
}

// CodeAndCodeHash struct to hold codehash => code mappings
type CodeAndCodeHash struct {
    Hash common.Hash
    Code []byte
}

Usage

The service is started when the plugin library is loaded by PluGeth and runs as an auxiliary component of the node as it syncs.

CLI configuration

This service introduces a CLI flag namespace statediff. Note that PluGeth plugin arguments must be separated from geth arguments by --, e.g. geth --datadir data -- --statediff.

• --statediff is used to enable the service
• --statediff.writing is used to tell the service to write state diff objects it produces from synced ChainEvents directly to a configured Postgres database
• --statediff.workers is used to set the number of concurrent workers to process state diff objects and write them into the database
• --statediff.db.type is the type of database we write out to (current options: postgres, dump, file)
• --statediff.dump.dst is the destination to write to when operating in database dump mode (stdout, stderr, discard)
• --statediff.db.driver is the specific driver to use for the database (current options for postgres: pgx and sqlx)
• --statediff.db.host is the hostname address to dial to connect to the database
• --statediff.db.port is the port to dial to connect to the database
• --statediff.db.name is the name of the database to connect to
• --statediff.db.user is the user to connect to the database as
• --statediff.db.password is the password to use to connect to the database
• --statediff.db.conntimeout is the connection timeout (in seconds)
• --statediff.db.maxconns is the maximum number of database connections
• --statediff.db.minconns is the minimum number of database connections
• --statediff.db.maxidleconns is the maximum number of idle connections
• --statediff.db.maxconnidletime is the maximum lifetime for an idle connection (in seconds)
• --statediff.db.maxconnlifetime is the maximum lifetime for a connection (in seconds)
• --statediff.db.nodeid is the node id to use in the Postgres database
• --statediff.db.clientname is the client name to use in the Postgres database
• --statediff.db.upsert whether or not the service, when operating in a direct database writing mode, should overwrite any existing conflicting data
• --statediff.file.path full path (including filename) to write statediff data out to when operating in file mode
• --statediff.file.wapath full path (including filename) to write statediff watched addresses out to when operating in file mode

The service can only operate in full sync mode (--syncmode=full), but only the historical RPC endpoints require an archive node (--gcmode=archive)

e.g. geth --syncmode=full --gcmode=archive -- --statediff --statediff.writing --statediff.db.type=postgres --statediff.db.driver=sqlx --statediff.db.host=localhost --statediff.db.port=5432 --statediff.db.name=cerc_testing --statediff.db.user=postgres --statediff.db.nodeid=nodeid --statediff.db.clientname=clientname

When operating in --statediff.db.type=file mode, the service will save SQL statements to the file specified by --statediff.file.path. It's important to note that these SQL statements are written without any ON CONFLICT constraint checks. This omission allows us to:

• horizontally expand the production of SQL statements,
• merge the individual SQL files generated,
• remove duplicates using Unix tools (sort statediff.sql | uniq or sort -u statediff.sql),
• perform bulk loading using psql (psql db_name --set ON_ERROR_STOP=on -f statediff.sql),
• and then reinstate our primary and foreign key constraints and indexes.

Payload retrieval

The state diffing service exposes both a websocket subscription endpoint, and a number of HTTP unary endpoints for retrieving data payloads.

Each of these endpoints requires a set of parameters provided by the caller:

// Params is used to carry in parameters from subscribing/requesting clients configuration
type Params struct {
    IntermediateStateNodes   bool
    IntermediateStorageNodes bool
    IncludeBlock             bool
    IncludeReceipts          bool
    IncludeTD                bool
    IncludeCode              bool
    WatchedAddresses         []common.Address
}

Using these params we can tell the service:

• whether to include state and/or storage intermediate nodes
• whether to include the associated block (header, uncles, and transactions)
• whether to include the associated receipts
• whether to include the total difficulty for this block
• whether to include the set of code hashes and code for contracts deployed in this block, and
• whether to limit the diffing process to a list of specific addresses.

Subscription endpoints

A websocket-supporting RPC endpoint is exposed for subscribing to state diff StateObjects that come off the head of the chain while the geth node syncs.

// Stream is a subscription endpoint that fires off state diff payloads as they are created
Stream(ctx context.Context, params Params) (*rpc.Subscription, error)

To expose this endpoint the node needs to have the websocket server turned on (--ws), and the statediff namespace exposed (--ws.api=statediff).

Go code subscriptions to this endpoint can be created using the rpc.Client.Subscribe() method, with the "statediff" namespace, a statediff.Payload channel, and the name of the statediff api's rpc method: "stream".

e.g.

cli, err := rpc.Dial("ipcPathOrWsURL")
if err != nil {
    // handle error
}
stateDiffPayloadChan := make(chan statediff.Payload, 20000)
methodName := "stream"
params := statediff.Params{
    IncludeBlock:             true,
    IncludeTD:                true,
    IncludeReceipts:          true,
    IntermediateStorageNodes: true,
    IntermediateStateNodes:   true,
}
rpcSub, err := cli.Subscribe(context.Background(), statediff.APIName, stateDiffPayloadChan, methodName, params)
if err != nil {
    // handle error
}
for {
    select {
    case stateDiffPayload := <- stateDiffPayloadChan:
        // process the payload
    case err := <- rpcSub.Err():
        // handle rpc subscription error
    }
}

Additionally, the StreamCodeAndCodeHash subscription method streams codehash-to-code pairs at a given block to a websocket channel.

Unary endpoints

The service also exposes unary RPC endpoints for retrieving the state diff StateObject for a specific block height/hash.

// StateDiffAt returns a state diff payload at the specific blockheight
StateDiffAt(ctx context.Context, blockNumber uint64, params Params) (*Payload, error)

// StateDiffFor returns a state diff payload for the specific blockhash
StateDiffFor(ctx context.Context, blockHash common.Hash, params Params) (*Payload, error)

To expose this endpoint the node needs to have the HTTP server turned on (--http), and the statediff namespace exposed (--http.api=statediff).

Direct indexing into Postgres

If --statediff.writing is enabled, the service will convert the StateObjects and all associated data into IPLD objects, persist them directly to Postgres, and generate secondary indexes around the IPLD data.

The schema and migrations for this Postgres database are defined in https://github.com/cerc-io/ipld-eth-db.

RPC endpoints

If enabled, direct indexing will be triggered on every ChainEvent, writing diffs for all new blocks as they are received. However, the service also provides methods for clients to trigger and track this process:

• The WriteStateDiffAt method directly writes a state diff object to the database at a specific block height.
• Likewise, the WriteStateDiffFor method directly writes a state diff object to the database for a specific block hash
• The StreamWrites method sets up a subscription to stream the status of completed calls to the above methods.
• The WatchAddress method enables the modification of the watched addresses list, restricting direct indexing for a given operation and arguments.

Schema overview

Our Postgres schemas are built around a single IPFS backing Postgres IPLD blockstore table (ipld.blocks) that conforms with go-ds-sql. All IPLD objects are stored in this table, where key is the blockstore-prefixed multihash key for the IPLD object and data contains the bytes for the IPLD block (in the case of all Ethereum IPLDs, this is the RLP byte encoding of the Ethereum object).

The IPLD objects in this table can be traversed using an IPLD DAG interface, but since this table only maps CID to raw IPLD object it is not very suitable for looking up Ethereum objects by their constituent fields (e.g. by tx source/recipient, state/storage trie path). To improve the accessibility of these objects we create an Ethereum advanced data layout (ADL) by generating secondary indexes on top of the raw IPLDs in other Postgres tables.

These secondary index tables fall under the eth schema and follow an {objectType}_cids naming convention. These tables provide a view into individual fields of the underlying Ethereum IPLD objects, allowing lookups on these fields, and reference the raw IPLD objects stored in ipld.blocks by CID. Additionally, these tables maintain the hash-linked nature of Ethereum objects to one another, e.g. a storage trie node entry in the storage_cids table contains a state_leaf_key field referencing the state_cids entry for the state trie node of its owning contract, and that state_cids entry in turn contains a header_id field referencing the block_hash of the header_cids entry for the block in which these state and storage nodes were updated (diffed).

Optimization

On mainnet this process is extremely IO intensive and requires significant resources to allow it to keep up with the head of the chain. The state diff processing time for a specific block is dependent on the number and complexity of the state changes that occur in a block and the number of updated state nodes that are available in the in-memory cache vs must be retrieved from disc.

If memory permits, one means of improving the efficiency of this process is to increase the in-memory trie cache allocation. This can be done by increasing the overall --cache allocation and/or by increasing the % of the cache allocated to trie usage with --cache.trie.