Indexing Transactions
=====================

Tendermint allows you to index transactions and later query or subscribe to
their results.

Let's take a look at the ``[tx_index]`` config section:

::

    ##### transactions indexer configuration options #####
    [tx_index]

    # What indexer to use for transactions
    #
    # Options:
    #   1) "null" (default)
    #   2) "kv" - the simplest possible indexer, backed by key-value storage (defaults to levelDB; see DBBackend).
    indexer = "kv"

    # Comma-separated list of tags to index (by default the only tag is tx hash)
    #
    # It's recommended to index only a subset of tags due to possible memory
    # bloat. This is, of course, depends on the indexer's DB and the volume of
    # transactions.
    index_tags = ""

    # When set to true, tells indexer to index all tags. Note this may be not
    # desirable (see the comment above). IndexTags has a precedence over
    # IndexAllTags (i.e. when given both, IndexTags will be indexed).
    index_all_tags = false

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 tags
-----------

In your application's ``DeliverTx`` method, add the ``Tags`` field with the
pairs of UTF-8 encoded strings (e.g. "account.owner": "Bob", "balance":
"100.0", "date": "2018-01-02").

Example:

::

    func (app *KVStoreApplication) DeliverTx(tx []byte) types.Result {
        ...
        tags := []cmn.KVPair{
          {[]byte("account.name"), []byte("igor")},
          {[]byte("account.address"), []byte("0xdeadbeef")},
          {[]byte("tx.amount"), []byte("7")},
        }
        return types.ResponseDeliverTx{Code: code.CodeTypeOK, Tags: tags}
    }

If you want Tendermint to only index transactions by "account.name" tag, in the
config set ``tx_index.index_tags="account.name"``. If you to index all tags,
set ``index_all_tags=true``

Note, there are a few predefined tags:

- ``tm.event`` (event type)
- ``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.

Quering transactions
--------------------

You can query the transaction results by calling ``/tx_search`` RPC endpoint:

::

    curl "localhost:46657/tx_search?query=\"account.name='igor'\"&prove=true"

Check out `API docs <https://tendermint.github.io/slate/?shell#txsearch>`__ 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": "account.name='igor'"
        }
    }

Check out `API docs <https://tendermint.github.io/slate/#subscribe>`__ for more
information on query syntax and other options.