Ingest data into a Timescale Cloud service

This tutorial uses a dataset that contains second-by-second stock-trade data for the top 100 most-traded symbols, in a hypertable named stocks_real_time. It also includes a separate table of company symbols and company names, in a regular PostgreSQL table named company.

Prerequisites

To follow the steps on this page:

Create a target Timescale Cloud service with time-series and analytics enabled.
You need your connection details. This procedure also works for self-hosted TimescaleDB.

Connect to the websocket server

When you connect to the Twelve Data API through a websocket, you create a persistent connection between your computer and the websocket server. You set up a Python environment, and pass two arguments to create a websocket object and establish the connection.

Set up a new Python environment

Create a new Python virtual environment for this project and activate it. All the packages you need to complete for this tutorial are installed in this environment.

Create and activate a Python virtual environment:
```
virtualenv env
source env/bin/activate
```
Install the Twelve Data Python wrapper library with websocket support. This library allows you to make requests to the API and maintain a stable websocket connection.
```
pip install twelvedata websocket-client
```
Install Psycopg2 so that you can connect the TimescaleDB from your Python script:
```
pip install psycopg2-binary
```

Create the websocket connection

A persistent connection between your computer and the websocket server is used to receive data for as long as the connection is maintained. You need to pass two arguments to create a websocket object and establish connection.

Websocket arguments

on_event
This argument needs to be a function that is invoked whenever there's a new data record is received from the websocket:
```
def on_event(event):
    print(event) # prints out the data record (dictionary)
```
This is where you want to implement the ingestion logic so whenever there's new data available you insert it into the database.
symbols
This argument needs to be a list of stock ticker symbols (for example, MSFT) or crypto trading pairs (for example, BTC/USD). When using a websocket connection you always need to subscribe to the events you want to receive. You can do this by using the symbols argument or if your connection is already created you can also use the subscribe() function to get data for additional symbols.

Connect to the websocket server

Create a new Python file called websocket_test.py and connect to the Twelve Data servers using the <YOUR_API_KEY>:


import time
   from twelvedata import TDClient

    messages_history = []

    def on_event(event):
     print(event) # prints out the data record (dictionary)
     messages_history.append(event)

   td = TDClient(apikey="<YOUR_API_KEY>")
   ws = td.websocket(symbols=["BTC/USD", "ETH/USD"], on_event=on_event)
   ws.subscribe(['ETH/BTC', 'AAPL'])
   ws.connect()
   while True:
   print('messages received: ', len(messages_history))
   ws.heartbeat()
   time.sleep(10)

Run the Python script:
```
python websocket_test.py
```

When you run the script, you receive a response from the server about the status of your connection:


{'event': 'subscribe-status',
 'status': 'ok',
 'success': [
        {'symbol': 'BTC/USD', 'exchange': 'Coinbase Pro', 'mic_code': 'Coinbase Pro', 'country': '', 'type': 'Digital Currency'},
        {'symbol': 'ETH/USD', 'exchange': 'Huobi', 'mic_code': 'Huobi', 'country': '', 'type': 'Digital Currency'}
    ],
 'fails': None
}

When you have established a connection to the websocket server, wait a few seconds, and you can see data records, like this:


{'event': 'price', 'symbol': 'BTC/USD', 'currency_base': 'Bitcoin', 'currency_quote': 'US Dollar', 'exchange': 'Coinbase Pro', 'type': 'Digital Currency', 'timestamp': 1652438893, 'price': 30361.2, 'bid': 30361.2, 'ask': 30361.2, 'day_volume': 49153}
{'event': 'price', 'symbol': 'BTC/USD', 'currency_base': 'Bitcoin', 'currency_quote': 'US Dollar', 'exchange': 'Coinbase Pro', 'type': 'Digital Currency', 'timestamp': 1652438896, 'price': 30380.6, 'bid': 30380.6, 'ask': 30380.6, 'day_volume': 49157}
{'event': 'heartbeat', 'status': 'ok'}
{'event': 'price', 'symbol': 'ETH/USD', 'currency_base': 'Ethereum', 'currency_quote': 'US Dollar', 'exchange': 'Huobi', 'type': 'Digital Currency', 'timestamp': 1652438899, 'price': 2089.07, 'bid': 2089.02, 'ask': 2089.03, 'day_volume': 193818}
{'event': 'price', 'symbol': 'BTC/USD', 'currency_base': 'Bitcoin', 'currency_quote': 'US Dollar', 'exchange': 'Coinbase Pro', 'type': 'Digital Currency', 'timestamp': 1652438900, 'price': 30346.0, 'bid': 30346.0, 'ask': 30346.0, 'day_volume': 49167}

Each price event gives you multiple data points about the given trading pair such as the name of the exchange, and the current price. You can also occasionally see heartbeat events in the response; these events signal the health of the connection over time. At this point the websocket connection is working successfully to pass data.

Optimize time-series data in a hypertable

Hypertables are the core of TimescaleDB, they enable Timescale Cloud to work efficiently with time-series data. Hypertables are PostgreSQL tables that automatically partition your time-series data by time. When you run a query, Timescale Cloud identifies the correct partition and runs the query on it, instead of going through the entire table.

Because TimescaleDB is 100% PostgreSQL, you can create standard PostgreSQL tables, indexes, stored procedures, and other objects alongside your Timescale hypertables. This makes creating and working with hypertables similar to standard PostgreSQL.

Connect to your Timescale Cloud service.
In Timescale Console open an SQL editor. You can also connect to your service using psql.

Create a standard PostgreSQL table to store the real-time cryptocurrency data:


CREATE TABLE crypto_ticks (
    "time" TIMESTAMPTZ,
    symbol TEXT,
    price DOUBLE PRECISION,
    day_volume NUMERIC
);

Convert the standard table into a hypertable partitioned on the time column using the create_hypertable() function provided by Timescale. You must provide the name of the table and the column in that table that holds the timestamp data to use for partitioning:
```
SELECT create_hypertable('crypto_ticks', by_range('time'));
```

Create a standard PostgreSQL table for relational data

When you have relational data that enhances your time-series data, store that data in standard PostgreSQL relational tables.

Add a table to store the asset symbol and name in a relational table:


CREATE TABLE crypto_assets (
    symbol TEXT UNIQUE,
    "name" TEXT
);

You now have two tables within your Timescale Cloud service. A hypertable named crypto_ticks, and a normal PostgreSQL table named crypto_assets.

When you ingest data into a transactional database like Timescale, it is more efficient to insert data in batches rather than inserting data row-by-row. Using one transaction to insert multiple rows can significantly increase the overall ingest capacity and speed of your Timescale database.

Batching in memory

A common practice to implement batching is to store new records in memory first, then after the batch reaches a certain size, insert all the records from memory into the database in one transaction. The perfect batch size isn't universal, but you can experiment with different batch sizes (for example, 100, 1000, 10000, and so on) and see which one fits your use case better. Using batching is a fairly common pattern when ingesting data into TimescaleDB from Kafka, Kinesis, or websocket connections.

To ingest the data into your Timescale service, you need to implement the on_event function.

After the websocket connection is set up, you can use the on_event function to ingest data into the database. This is a data pipeline that ingests real-time financial data into your Timescale service.

You can implement a batching solution in Python with Psycopg2. You can implement the ingestion logic within the on_event function that you can then pass over to the websocket object.

This function needs to:

Check if the item is a data item, and not websocket metadata.
Adjust the data so that it fits the database schema, including the data types, and order of columns.
Add it to the in-memory batch, which is a list in Python.
If the batch reaches a certain size, insert the data, and reset or empty the list.

Ingest data in real-time

Update the Python script that prints out the current batch size, so you can follow when data gets ingested from memory into your database. Use the <HOST>, <PASSWORD>, and <PORT> details for the Timescale service where you want to ingest the data and your API key from Twelve Data:


import time
import psycopg2

from twelvedata import TDClient
from psycopg2.extras import execute_values
from datetime import datetime

class WebsocketPipeline():
    # name of the hypertable
    DB_TABLE = "stocks_real_time"

    # columns in the hypertable in the correct order
    DB_COLUMNS=["time", "symbol", "price", "day_volume"]

    # batch size used to insert data in batches
    MAX_BATCH_SIZE=100

    def __init__(self, conn):
        """Connect to the Twelve Data web socket server and stream
        data into the database.

        Args:
            conn: psycopg2 connection object
        """
        self.conn = conn
        self.current_batch = []
        self.insert_counter = 0

    def _insert_values(self, data):
        if self.conn is not None:
            cursor = self.conn.cursor()
            sql = f"""
            INSERT INTO {self.DB_TABLE} ({','.join(self.DB_COLUMNS)})
            VALUES %s;"""
            execute_values(cursor, sql, data)
            self.conn.commit()

    def _on_event(self, event):
        """This function gets called whenever there's a new data record coming
        back from the server.

        Args:
            event (dict): data record
        """
        if event["event"] == "price":
            # data record
            timestamp = datetime.utcfromtimestamp(event["timestamp"])
            data = (timestamp, event["symbol"], event["price"], event.get("day_volume"))

            # add new data record to batch
            self.current_batch.append(data)
            print(f"Current batch size: {len(self.current_batch)}")

            # ingest data if max batch size is reached then reset the batch
            if len(self.current_batch) == self.MAX_BATCH_SIZE:
                self._insert_values(self.current_batch)
                self.insert_counter += 1
                print(f"Batch insert #{self.insert_counter}")
                self.current_batch = []
        def start(self, symbols):
            """Connect to the web socket server and start streaming real-time data
            into the database.

            Args:
                symbols (list of symbols): List of stock/crypto symbols
            """
            td = TDClient(apikey="<YOUR_API_KEY")
            ws = td.websocket(on_event=self._on_event)
            ws.subscribe(symbols)
            ws.connect()
            while True:
               ws.heartbeat()
               time.sleep(10)
    onn = psycopg2.connect(database="tsdb",
                        host="<HOST>",
                        user="tsdbadmin",
                        password="<PASSWORD>",
                        port="<PORT>")

    symbols = ["BTC/USD", "ETH/USD", "MSFT", "AAPL"]
    websocket = WebsocketPipeline(conn)
    websocket.start(symbols=symbols)
    ```

Run the script:
```
python websocket_test.py
```

You can even create separate Python scripts to start multiple websocket connections for different types of symbols, for example, one for stock, and another one for cryptocurrency prices.

Troubleshooting

If you see an error message similar to this:


2022-05-13 18:51:41,976 - ws-twelvedata - ERROR - TDWebSocket ERROR: Handshake status 200 OK

Then check that you use a proper API key received from Twelve Data.

Connect Grafana to Timescale Cloud

To visualize the results of your queries, enable Grafana to read the data in your service:

Log in to Grafana
In your browser, log in to either:
- Self-hosted Grafana: at http://localhost:3000/. The default credentials are admin, admin.
- Grafana Cloud: use the URL and credentials you set when you created your account.
Add your service as a data source
1. Open Connections > Data sources, then click Add new data source.
2. Select PostgreSQL from the list.
3. Configure the connection:
  - Host URL, Database name, Username, and Password
    Configure using your connection details. Host URL is in the format <host>:<port>.
  - TLS/SSL Mode: select require.
  - PostgreSQL options: enable TimescaleDB.
  - Leave the default setting for all other fields.
4. Click Save & test.
  Grafana checks that your details are set correctly.