QuestDB implements the InfluxDB line protocol to ingest data. This enables you to use QuestDB as a drop-in replacement for InfluxDB and others implementing the protocol.

It is not necessary to create a table schema beforehand: the table will be created on the fly. If new columns are added, the table is automatically updated to reflect the new structure.

QuestDB can listen for line protocol packets both over TCP and UDP.



table_name,tagset fieldset timestamp
table_nameName of the table where QuestDB will write data.
tagsetArray of string key-value pairs separated by commas that represent the reading's associated metadata
fieldsetArray of key-value pairs separated by commas that represent readings. The keys are string, values can be string, numeric or boolean
timestampUNIX timestamp. By default in nanoseconds. Can be changed in the configuration


  • When the table_name does not correspond to an existing table, QuestDB will create the table on the fly using the name provided. Column types will be automatically recognized and assigned based on the data.
  • The timestamp column is automatically created as designated timestamp with the partition strategy set to NONE. If you would like to define a partition strategy, you should CREATE the table beforehand.
  • When the timestamp is empty, QuestDB will use the server timestamp.

Generic example#

Let's assume the following data:


The line protocol syntax for that table is:

readings,city=London,make=Omron temperature=23.5,humidity=0.343 1465839830100400000
readings,city=Bristol,make=Honeywell temperature=23.2,humidity=0.443 1465839830100600000
readings,city=London,make=Omron temperature=23.6,humidity=0.348 1465839830100700000

Irregularly-structured data#

InfluxDB line protocol makes it possible to send data under different shapes. Each new entry may contain certain metadata tags or readings, and others not. QuestDB can support on-the-fly data structure changes with minimal overhead. Whilst the example just above highlights structured data, it is possible for InfluxDB line protocol users to send data as follows:

readings,city=London temperature=23.2 1465839830100400000
readings,city=London temperature=23.6 1465839830100700000
readings,make=Honeywell temperature=23.2,humidity=0.443 1465839830100800000

This would result in the following table:


Whilst we offer this function for flexibility, we recommend that users try to minimise structural changes to maintain operational simplicity.

TCP receiver#

The TCP receiver can handle both single and multi-row write requests. It is fully multi-threaded and customizable. It can work from the common worker pool or out of dedicated threads. A load balancing mechanism dynamically assigns work between the threads.


By default, QuestDB listens to line protocol packets over TCP on If you are running QuestDB with Docker, you will need to publish the port 9009 using -p 9009:9009. This port can be customized.


Although the original protocol does not support it, we added authentication for our TCP users. This works by using an elliptic curve P-256 JSON Web Token (JWT) to sign a server challenge.


In order to use this feature, you need to create an authentication file using the following template:

# [key/user id] [key type] {key details} ...
testUser1 ec-p-256-sha256 fLKYEaoEb9lrn3nkwLDA-M_xnuFOdSt9y0Z7_vWSHLU Dt5tbS1dEDMSYfym3fgMv0B99szno-dFc1rYF9t0aac

Only elliptic curve (for curve P-256) are supported (key type ec-p-256-sha256). This algorithm is also called ES256.

Once you created the file, you will need to reference it in the configuration for the key line.tcp.auth.db.path. Example: line.tcp.auth.db.path=conf/auth.txt.


For the server configuration above, the corresponding JSON Web Key stored on the client would be:

"kty": "EC",
"d": "5UjEMuA0Pj5pjK8a-fa24dyIf-Es5mYny3oE_Wmus48",
"crv": "P-256",
"kid": "testUser1",
"x": "fLKYEaoEb9lrn3nkwLDA-M_xnuFOdSt9y0Z7_vWSHLU",
"y": "Dt5tbS1dEDMSYfym3fgMv0B99szno-dFc1rYF9t0aac"

For this kind of key, the d parameter is used to generate the the secret key. The x and y parameters are used to generate the public key (values that we retrieve in the server authentication file).

Generate a JSON Web Key#

To create a JSON Web Key, you can use this online generator. Alternatively, you can use this 3rd party website (please select EC -> P-256 -> Encryption -> ES256). For production use, we recommend that you generate your keys using OpenSSL.

Final steps#

The server will now expect the client to send its key id (terminated with \n) straight after connect(). The server will respond with a challenge (printable characters terminated with \n). The client needs to sign the challenge and respond to the server with the base64 encoded signature (terminated with \n). If all is good the client can then continue, if not the server will disconnect and log the failure.

Load balancing#

A load balancing job reassigns work between threads in order to relieve the busiest threads and maintain high ingestion speed. It can be triggered in two ways.

  • After a certain number of updates per table
  • After a certain amount of time has passed

Once either is met, QuestDB will calculate a load ratio as the number of writes by the busiest thread divided by the number of writes in the least busy thread. If this ratio is above the threshold, the table with the least writes in the busiest worker thread will be reassigned to the least busy worker thread.

InfluxDB line protocol load balancing diagram

Commit strategy#

Uncommitted rows are committed either:

  • after milliseconds have passed
  • once reaching line.tcp.max.uncommitted.rows uncommitted rows.


The TCP receiver configuration can be completely customized using configuration keys. You can use this to configure the tread pool, buffer and queue sizes, receiver IP address and port, load balancing etc.


Please check or Develop section:

UDP receiver#

The UDP receiver can handle both single and multi row write requests. It is currently single-threaded, and performs both network IO and write jobs out of one thread. The UDP worker thread can work either on its own thread or use the common thread pool. It supports both multicast and unicast.


By default, QuestDB listens for multicast line protocol packets over UDP on If you are running QuestDB with Docker, you will need to publish the port 9009 using -p 9009:9009 and publish multicast packets with TTL of at least 2. This port can be customized, and you can also configure QuestDB to listen for unicast.

Commit strategy#

Uncommitted rows are committed either:

  • after receiving a number of continuous messages equal to line.udp.commit.rate
  • when messages are no longer being received


The UDP receiver configuration can be completely customized using configuration keys. You can use this to configure the IP address and port the receiver binds to, commit rates, buffer size, whether it should run on a separate thread etc.


Find an example of how to use this in the InfluxDB sender library section.