QuestDB

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Overview

A client-mode connector for the QuestDB HTTP REST API that streams MQTT telemetry into QuestDB tables and runs SQL from MQTT:

Catalog connector event	Endpoint	Notes
POST write (ILP)	`POST /write?precision=`	ILP over HTTP, `text/plain` line protocol body, `204` on success. Tables and columns auto-create.
GET exec	`GET /exec?query=`	SQL (SELECT, INSERT, CREATE TABLE) returning JSON `columns` + `dataset`
GET exp	`GET /exp?query=`	SQL result as CSV
GET ping	`GET /ping`	Health check, `204`

Default BASE_ADDRESS is http://YOUR_QUESTDB_HOST:9000 (QuestDB’s HTTP port). Topics use data/questdb/<object>/<verb>.

CSV import (/imp) is not a client event. QuestDB only accepts multipart/form-data uploads on /imp; a raw body returns 400 Non-multipart POST not supported. Use ILP /write for streaming rows, or /exec with INSERT INTO … for small batches.

Auth

QuestDB open source has no HTTP auth by default. When you enable http.user / http.password (OSS) or RBAC (QuestDB Enterprise), pass the full header value in authorization, such as Basic base64(user:pass) or Bearer <REST token>. Send an empty string when the server has no auth. Keep the value in a Hub secret such as QUESTDB_AUTH and never commit it.

Basic Syntax

DEFINE ROUTE QuestdbRestApi WITH TYPE REST_API
    ADD REST_API_CONFIG
        WITH BASE_ADDRESS "http://YOUR_QUESTDB_HOST:9000"
        WITH ENABLE_CLIENT "true"
        WITH USE_SSL "false"
        WITH REQUEST_TIMEOUT '60'
        WITH DEFAULT_CONTENT_TYPE "application/json"
    ADD EVENT Ping
        WITH SOURCE_TOPIC "data/questdb/ping"
        WITH DESTINATION_TOPIC "data/questdb/ping/response"
        WITH METHOD "GET"
        WITH ENDPOINT "/ping"
        WITH HEADERS
            ADD "Authorization" "{value.json.authorization}"
    ADD EVENT ExecQuery
        WITH SOURCE_TOPIC "data/questdb/query/exec"
        WITH DESTINATION_TOPIC "data/questdb/query/exec/response"
        WITH METHOD "GET"
        WITH ENDPOINT "/exec?query={value.json.query}&count=true"
        WITH HEADERS
            ADD "Accept" "application/json"
            ADD "Authorization" "{value.json.authorization}"
    ADD EVENT WriteIlp
        WITH SOURCE_TOPIC "data/questdb/ilp/write"
        WITH DESTINATION_TOPIC "data/questdb/ilp/write/response"
        WITH METHOD "POST"
        WITH ENDPOINT "/write?precision={value.json.precision}"
        WITH HEADERS
            ADD "Content-Type" "text/plain; charset=utf-8"
            ADD "Authorization" "{value.json.authorization}"
        WITH BODY "{payload}"
    ADD EVENT ExportCsv
        WITH SOURCE_TOPIC "data/questdb/query/export"
        WITH DESTINATION_TOPIC "data/questdb/query/export/response"
        WITH METHOD "GET"
        WITH ENDPOINT "/exp?query={value.json.query}"
        WITH HEADERS
            ADD "Accept" "text/csv"
            ADD "Authorization" "{value.json.authorization}"

Example MQTT payloads

Write telemetry (topic data/questdb/ilp/write). JSON fields fill the query placeholders; the body is line protocol:

{ "authorization": "", "precision": "ms" }

factory_smoke,site=porto value=21.5 1791234567890

SQL query (topic data/questdb/query/exec). URL-encode the SQL before publishing:

{ "authorization": "", "query": "SELECT%20site,value%20FROM%20factory_smoke%20LIMIT%2010" }

The response topic receives QuestDB’s JSON, for example {"columns":[…],"dataset":[["porto",21.5]],"count":1}. CSV export (topic data/questdb/query/export) takes the same payload as exec. Health (topic data/questdb/ping) takes { "authorization": "" }.

Testing

The factory smoke ran against a local QuestDB 10.0.1 instance: GET /ping returned 204, CREATE TABLE through /exec returned 200, an ILP POST /write?precision=ms returned 204, and the row came back through /exec (200 JSON) and /exp (200 CSV).

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Overview

Auth

Basic Syntax

Example MQTT payloads

Testing

​Overview

​Auth

​Basic Syntax

​Example MQTT payloads

​Testing

​Related

Overview

Auth

Basic Syntax

Example MQTT payloads

Testing

Related