QuestDB Wire Protocol (QWP)

QWP is QuestDB's columnar binary protocol for high-throughput data ingestion (/write/v4) and streaming query results (/read/v1) over WebSocket and UDP. These properties control protocol limits and the UDP receiver. WebSocket ingestion and egress share the HTTP server's network settings (port, TLS, worker threads); see HTTP server configuration for those.

Protocol limits​

qwp.max.rows.per.table​

  • Default: 1000000
  • Reloadable: no

Maximum number of rows per table block in a single QWP message. The server rejects batches that exceed this limit with a parse error.

qwp.max.schemas.per.connection​

  • Default: 65535
  • Reloadable: no

Maximum number of distinct schemas the server registers per connection. Each unique combination of column names and types consumes one schema slot. When the limit is reached, the server rejects further full-schema messages. For egress connections, a lower soft cap (4,096 by default) triggers a CACHE_RESET frame that clears and restarts the registry before hitting this hard limit.

qwp.max.tables.per.connection​

  • Default: 10000
  • Reloadable: no

Maximum number of distinct tables a single connection may write to. The server rejects messages referencing additional tables once this limit is reached.

UDP receiver​

note

The QWP UDP receiver is a fire-and-forget ingestion path for metrics workloads where occasional message loss is acceptable. It is disabled by default. For reliable ingestion, use the WebSocket transport.

qwp.udp.bind.to​

  • Default: 0.0.0.0:9007
  • Reloadable: no

IP address and port the UDP receiver binds to. The default listens on all network interfaces on port 9007.

qwp.udp.commit.interval​

  • Default: 2000 (milliseconds)
  • Reloadable: no

Time interval between commits for data received over UDP. Lower values reduce the window of uncommitted data at the cost of more frequent I/O.

qwp.udp.enabled​

  • Default: false
  • Reloadable: no

Enable or disable the QWP UDP receiver.

qwp.udp.join​

  • Default: 224.1.1.1
  • Reloadable: no

Multicast group address the UDP receiver joins. Only relevant when qwp.udp.unicast is false.

qwp.udp.max.uncommitted.datagrams​

  • Default: 1048576
  • Reloadable: no

Maximum number of uncommitted datagrams before the receiver forces a commit, regardless of the time-based commit interval.

qwp.udp.msg.buffer.size​

  • Default: 65536 (bytes)
  • Reloadable: no

Size of each message buffer allocated for the UDP receiver.

qwp.udp.msg.count​

  • Default: 10000
  • Reloadable: no

Number of message buffers to pre-allocate. Higher values absorb larger bursts at the cost of more memory.

qwp.udp.own.thread​

  • Default: true
  • Reloadable: no

When true, the UDP receiver runs in a dedicated thread with a busy-spin loop for lowest latency. When false, the receiver uses the shared worker pool.

qwp.udp.own.thread.affinity​

  • Default: -1 (no affinity)
  • Reloadable: no

CPU core affinity for the dedicated UDP receiver thread. A value of -1 lets the OS schedule the thread. Only applies when qwp.udp.own.thread is true.

qwp.udp.receive.buffer.size​

  • Default: -1 (OS default)
  • Reloadable: no

OS-level socket receive buffer size in bytes. A value of -1 uses the operating system's default. Increase this if you observe datagram drops under high throughput.

qwp.udp.unicast​

  • Default: true
  • Reloadable: no

When true, the UDP receiver operates in unicast mode. When false, it joins the multicast group specified by qwp.udp.join.