Photo by Ricardo Gomez Angel via Unsplash

note

The UDP receiver is deprecated since QuestDB version 6.5.2. We recommend the TCP receiver introduced by this article.

We've had a UDP version of the InfluxDB Line Protocol (ILP) reader in QuestDB for quite some time, but we've had customers ask for a TCP version of it, so we delivered!

Using and configuring it are relatively simple, so this tutorial will walk you through the basics of setting it up and using it. For an added bonus, we'll see how to migrate from using InfluxDB to using QuestDB with a single-line configuration change.

Configuring TCP InfluxDB line protocol listener

Here's the best part, at least for a basic implementation that you don't need to performance tune at all: It's already set up.

That's right, as soon as you start QuestDB, both the UDP and TCP ILP listeners start automatically on port 9009. Yes, TCP and UDP both use the same port. No, that's not a problem since one is UDP and one is TCP.

There are many configuration options you can tune in your conf/server.conf file if you're interested. I won't go through them here, but you can read all about them in our docs. I hope they are relatively self-explanatory.

InfluxDB line protocol refresher

If you have used ILP before, this should all be review. If you're new to ILP, this will tell you how you should write your data to QuestDB.

Basic structure

ILP syntax

table_name,tagset valueset timestamp

Pretty basic. So let's dive into what each element actually is and how to structure a line of ILP for writing.

The first element is the table_name portion, which tells the ILP writer which database table to write values into.

Next comes the set of tags you want to use. These are standard key=value pairs, and you can add as many of them as you want or need. Just separate them with commas.

There should only ever be 2 spaces in your line protocol. No more. The first space separates your tags from the values you want to associate with those tagss. The second space separates the values from the timestamp for those tags and values.

The values are also key=value pairs, and again you can send as many as you want in a line.

Finally comes your timestamp value, typically in µSeconds.

Example ILP

Let's use an example of writing some environmental data to QuestDB. I have a sensor that reads the temperature, atmospheric pressure, humidity, and altitude.

Reading	Value
Temperature	23.180000
Humidity	51.982422
Pressure	1002.112061
Altitude	93.146370

And I want to use the following tags:

Tag Name	Tag Value
dev_id	THP002
dev_loc	Apex
dev_name	BME280

And my table_name is iot

Now I have all the basic elements I need to construct my ILP, which will look like this:

iot,dev_id=THP002,dev_loc=Apex,dev_name=BME280 temp_c=23.18,altitude=93.10,humidity=52.16,pressure=1002.12

And yes, I rounded those values. But you'll notice that I did not add a timestamp value. In this case, it's because I am sending the values from a small, embedded sensor device that really doesn't have a great sense of time. By sending the ILP without a timestamp I'm telling the database itself to add one for me, using the timestamps arrival time.

Database structure

One of the cool features of using the ILP reader (well, QuestDB in general, really) is the ability to do 'Schema on Write'.

What that means is that if an ILP message arrives, QuestDB will automatically create tables and columns to fit the incoming ILP. So if you need to add a tag later, you can add it to the new device's tagset and start writing. The new tag will get added to the schema.

If you leave a tag value off, and it exists in the database, it will fill a null value.

When I start writing the above ILP to QuestDB, I'll get a table that looks like this:

dev_id	dev_name	temp_c	humidity	timestamp	dev_loc	altitude	pressure
THP002	BME280	26.52	51.94	2020-07-21T14:54:59.156202Z	Apex	76.27	1004.12
THP002	BME280	26.54	51.85	2020-07-21T14:54:59.157358Z	Apex	75.97	1004.16
THP002	BME280	26.56	51.83	2020-07-21T14:54:59.157389Z	Apex	75.84	1004.17
THP002	BME280	26.58	51.79	2020-07-21T14:54:59.287416Z	Apex	75.93	1004.16

This is what that table looks like in the QuestDB Web Console:

But how did you write that?

Oh, so how did I write that ILP to QuestDB? Well, my sensor is an Arduino, with a Bosch BME280 sensor attached. It is WiFi connected, so a WiFiClient can do the TCP write for me:

WiFiClient Connect

espClient.connect(Quest_Server, 9009);

Will connect the client to the QuestDB Server defined by Quest_Server on port 9009.

If I then have a line of ILP like this: iot,dev_id=THPL002,dev_loc=Demo,dev_name=BME280 temp_c=23.18,altitude=93.10,humidity=52.16,pressure=1002.12\n in a buffer I can call espClient.printf(buffer); and that line of data will be written to QuestDB.

Can I do batch writes?

Of course, you can! Put each line of ILP on a separate 'line', separated by a newline \n, and then when you have all your batch built up, write the whole thing to QuestDB.

Of course, if you're relying on QuestDB to add timestamps for you, then be aware that QuestDB will give the entire batch sequential timestamps based on when they are read/written to the database.

Conclusions

InfluxDB Line Protocol (ILP) is a simple, well-known, and relatively compact data format for sending Time Series data to a database. That's why we decided to support it.

I'm now going to give you a simple configuration change to migrate from using InfluxDB to using QuestDB. If you're using Telegraf as a data collector, we have documentation for integrating with QuestDB for more details, but to summarize the migration, edit telegraf.conf (it may be in different places, depending on your operating system) and change the line:

[[outputs.influxdb]]

urls = ["http://127.0.0.1:8086"]

to be:

[[outputs.socket_writer]]

address = "tcp://127.0.0.1:9009"

That's it. That's the migration. All data that was previously being written to InfluxDB will now be written to QuestDB.