Indexing Transactions

CometBFT allows you to index transactions and blocks and later query or subscribe to their results. Transactions are indexed by ResponseFinalizeBlock.tx_results.events and blocks are indexed by ResponseFinalizeBlock.events. However, transactions are also indexed by a primary key which includes the transaction hash and maps to and stores the corresponding transaction results. Blocks are indexed by a primary key which includes the block height and maps to and stores the block height, i.e. the block itself is never stored.

Each event contains a type and a list of attributes, which are key-value pairs denoting something about what happened during the method’s execution. For more details on Events, see the ABCI documentation.

An Event has a composite key associated with it. A compositeKey is constructed by its type and key separated by a dot.

For example:

"jack": [
  "account.number": 100
]

would be equal to the composite key of jack.account.number.

By default, CometBFT will index all transactions by their respective hashes and height and blocks by their height.

CometBFT allows for different events within the same height to have equal attributes.

Configuration

Operators can configure indexing via the [tx_index] section. The indexer field takes a series of supported indexers. If null is included, indexing will be turned off regardless of other values provided.

[tx-index]

# The backend database to back the indexer.
# If indexer is "null", no indexer service will be used.
#
# The application will set which txs to index. In some cases a node operator will be able
# to decide which txs to index based on configuration set in the application.
#
# Options:
#   1) "null"
#   2) "kv" (default) - the simplest possible indexer, backed by key-value storage (defaults to levelDB; see DBBackend).
#     - When "kv" is chosen "tx.height" and "tx.hash" will always be indexed.
#   3) "psql" - the indexer services backed by PostgreSQL.
# indexer = "kv"

Supported Indexers

KV

The kv indexer type is an embedded key-value store supported by the main underlying CometBFT database. Using the kv indexer type allows you to query for block and transaction events directly against CometBFT’s RPC. However, the query syntax is limited and so this indexer type might be deprecated or removed entirely in the future.

Implementation and data layout

The kv indexer stores each attribute of an event individually, by creating a composite key with

• event type,
• attribute key,
• attribute value,
• event generator (e.g. FinalizeBlock)
• the height, and
• event counter. For example the following events:

Type: "transfer",
  Attributes: []abci.EventAttribute{
   {Key: "sender", Value: "Bob", Index: true},
   {Key: "recipient", Value: "Alice", Index: true},
   {Key: "balance", Value: "100", Index: true},
   {Key: "note", Value: "nothing", Index: true},
   },

Type: "transfer",
  Attributes: []abci.EventAttribute{
   {Key: "sender", Value: "Tom", Index: true},
   {Key: "recipient", Value: "Alice", Index: true},
   {Key: "balance", Value: "200", Index: true},
   {Key: "note", Value: "nothing", Index: true},
   },

will be represented as follows in the store, assuming these events result from the FinalizeBlock call for height 1:

Key                                 value
---- event1 ------
transferSenderBobFinalizeBlock11           1
transferRecipientAliceFinalizeBlock11      1
transferBalance100FinalizeBlock11          1
transferNodeNothingFinalizeBlock11         1
---- event2 ------
transferSenderTomFinalizeBlock12           1
transferRecepientAliceFinalizeBlock12      1
transferBalance200FinalizeBlock12          1
transferNodeNothingFinalizeBlock12         1

The event number is a local variable kept by the indexer and incremented when a new event is processed. It is an int64 variable and has no other semantics besides being used to associate attributes belonging to the same events within a height. This variable is not atomically incremented as event indexing is deterministic. Should this ever change, the event id generation will be broken.

PostgreSQL

The psql indexer type allows an operator to enable block and transaction event indexing by proxying it to an external PostgreSQL instance allowing for the events to be stored in relational models. Since the events are stored in a RDBMS, operators can leverage SQL to perform a series of rich and complex queries that are not supported by the kv indexer type. Since operators can leverage SQL directly, searching is not enabled for the psql indexer type via CometBFT’s RPC – any such query will fail.

Note, the SQL schema is stored in state/indexer/sink/psql/schema.sql and operators must explicitly create the relations prior to starting CometBFT and enabling the psql indexer type.

Example:

psql ... -f state/indexer/sink/psql/schema.sql

Default Indexes

The CometBFT tx and block event indexer indexes a few select reserved events by default.

Transactions

The following indexes are indexed by default:

• tx.height
• tx.hash

Blocks

The following indexes are indexed by default:

• block.height

Adding Events

Applications are free to define which events to index. CometBFT does not expose functionality to define which events to index and which to ignore. In your application’s FinalizeBlock method, add the Events field with pairs of UTF-8 encoded strings (e.g. “transfer.sender”: “Bob”, “transfer.recipient”: “Alice”, “transfer.balance”: “100”).

Example:

func (app *Application) FinalizeBlock(_ context.Context, req *types.RequestFinalizeBlock) (*types.ResponseFinalizeBlock, error) {

    //...
  tx_results[0] := &types.ExecTxResult{
			Code: CodeTypeOK,
			// With every transaction we can emit a series of events. To make it simple, we just emit the same events.
			Events: []types.Event{
				{
					Type: "app",
					Attributes: []types.EventAttribute{
						{Key: "creator", Value: "Cosmoshi Netowoko", Index: true},
						{Key: "key", Value: key, Index: true},
						{Key: "index_key", Value: "index is working", Index: true},
						{Key: "noindex_key", Value: "index is working", Index: false},
					},
				},
				{
					Type: "app",
					Attributes: []types.EventAttribute{
						{Key: "creator", Value: "Cosmoshi", Index: true},
						{Key: "key", Value: value, Index: true},
						{Key: "index_key", Value: "index is working", Index: true},
						{Key: "noindex_key", Value: "index is working", Index: false},
					},
				},
			},
		}

    block_events = []types.Event{
			{
				Type: "loan",
				Attributes: []types.EventAttribute{
					{	Key:   "account_no", Value: "1", Index: true},
					{ Key:   "amount", Value: "200", Index: true },
				},
			},
			{
				Type: "loan",
				Attributes: []types.EventAttribute{
					{ Key:   "account_no", Value: "2",	Index: true },
					{ Key:   "amount", Value: "300", Index: true},
				},
			},
		}
    return &types.ResponseFinalizeBlock{TxResults: tx_results, Events: block_events}
}

If the indexer is not null, the transaction will be indexed. Each event is indexed using a composite key in the form of {eventType}.{eventAttribute}={eventValue}, e.g. transfer.sender=bob.

Querying Transactions Events

You can query for a paginated set of transaction by their events by calling the /tx_search RPC endpoint:

curl "localhost:26657/tx_search?query=\"message.sender='cosmos1...'\"&prove=true"

Check out API docs for more information on query syntax and other options.

Subscribing to Transactions

Clients can subscribe to transactions with the given tags via WebSocket by providing a query to /subscribe RPC endpoint.

{
  "jsonrpc": "2.0",
  "method": "subscribe",
  "id": "0",
  "params": {
    "query": "message.sender='cosmos1...'"
  }
}

Check out API docs for more information on query syntax and other options.

Querying Block Events

You can query for a paginated set of blocks by their events by calling the /block_search RPC endpoint:

curl "localhost:26657/block_search?query=\"block.height > 10\""

Storing the event sequence was introduced in CometBFT 0.34.26. Before that, up until Tendermint Core 0.34.26, the event sequence was not stored in the kvstore and events were stored only by height. That means that queries returned blocks and transactions whose event attributes match within the height but can match across different events on that height.

This behavior was fixed with CometBFT 0.34.26+. However, if the data was indexed with earlier versions of Tendermint Core and not re-indexed, that data will be queried as if all the attributes within a height occurred within the same event.

Event attribute value types

Users can use anything as an event value. However, if the event attribute value is a number, the following needs to be taken into account:

• Negative numbers will not be properly retrieved when querying the indexer.
• Event values are converted to big floats (from the big/math package). The precision of the floating point number is set to the bit length of the integer it is supposed to represent, so that there is no loss of information due to insufficient precision. This was not present before CometBFT v0.38.x and all float values were ignored.
• As of CometBFT v0.38.x, queries can contain floating point numbers as well.
• Note that comparing to floats can be imprecise with a high number of decimals.

Event type and attribute key format

An event type/attribute key is a string that can contain any Unicode letter or digit, as well as the following characters: . (dot), - (dash), _ (underscore). The event type/attribute key must not start with - (dash) or . (dot).

^[\w]+[\.-\w]?$