Apache IoTDB vs QuestDB

IoTDB runs two lines in parallel: 1.3.x carrying the original tree model and 2.0.x where nearly all new work lands. The 2.0 releases have been steadily building out the table model — set operations and common table expressions, window and pattern-recognition functions, JOIN variants including ASOF, approximate aggregates, user-defined table functions — turning what began as a time-series schema into something closer to a full SQL surface. Alongside that, an AINode component gained built-in forecasting models and inference for both models, and 2.0.10 added C-language driver SDK interfaces with parameter binding and multi-node failover.

Two audiences are being served at once. The table model work courts analysts and existing SQL tooling, with Spark integration and Python DataFrame returns as the connective tissue; the C driver and failover handling court the embedded and industrial systems that generate the data in the first place. The 1.3 branch now receives only what can be backported — the March security hardening shipped to both lines with identical notes — which reads as a maintenance line with a finite life. Security posture also tightened noticeably in 2.0.7, which removed risky RPC interfaces and JEXL functions and changed default bind addresses to loopback.

Expect continued SQL surface expansion in the table model and more client language coverage now that the C driver exists. The 1.3 branch's end is the open question these entries do not address.