# Indexing Transactions
Tendermint allows you to index transactions and later query or subscribe to their results.
Events can be used to index transactions and blocks according to what happened
during their execution. Note that the set of events returned for a block from
BeginBlock
and EndBlock
are merged. In case both methods return the same
type, only the key-value pairs defined in EndBlock
are used.
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]https://github.com/tendermint/tendermint/blob/main/spec/abci/abci.md#events) 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:
would be equal to the composite key of jack.account.number
.
Let's take a look at the [tx_index]
config section:
By default, Tendermint will index all transactions by their respective hashes using an embedded simple indexer. Note, we are planning to add more options in the future (e.g., PostgreSQL indexer).
# Adding Events
In your application's DeliverTx
method, add the Events
field with pairs of
UTF-8 encoded strings (e.g. "transfer.sender": "Bob", "transfer.recipient": "Alice",
"transfer.balance": "100").
Example:
If you want Tendermint to only index transactions by "transfer.sender" event type,
in the config set tx_index.index_tags="transfer.sender"
. If you to index all events,
set index_all_tags=true
Note, there are a few predefined event types:
tx.hash
(transaction's hash)tx.height
(height of the block transaction was committed in)
Tendermint will throw a warning if you try to use any of the above keys.
# Querying Transactions
You can query the transaction results by calling /tx_search
RPC endpoint:
Check out API docs (opens new window) 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.
Check out API docs (opens new window) for more information on query syntax and other options.