MQTT Performance Tests: Concurrent Connections

Connections

Connection tests measure how many client connections a broker can accept and how connect latency behaves as the number of concurrently connected clients grows. Each scenario connects clients in batches and records, per interval, how many connections completed and their average latency.

500K Connections

Server Host: 8xCPU, 20GB RAM
Clients Host: 8xCPU, 32GB RAM
MQTT Protocol: 3.1
MQTT QOS: 1
Port: 1884
Host: 8 CPU / 20Gb - the smaller pair, see the divider below
Max CPU: 17%
Max RAM: 2183 Mb
CPU percentages are of ONE core: 1600% = all 16 vCPU. xmq_server pins one thread
Version: 1.27.1
Date: 2026-09-17
CPU Load: 17% mean / 94% peak

NanoMQ timed out during the test. Only 395K clients completed connections.

Server	Version	CPU Load	Max RAM	Avg Connections	Avg Latency
Mosquitto 2.0.22-5build1	2.0.22-5build1	12% mean / 41% peak	428 Mb	500,000	348us
EMQX 5.8.9	5.8.9	230% mean / 702% peak	6792 Mb	500,000	717us
XMQ 0.9.18	0.9.18	25% mean / 100% peak	1378 Mb	500,000	293us
FlashMQ 1.27.1	1.27.1	17% mean / 91% peak	2183 Mb	500,000	293us

Mosquitto 2.0.22-5build1

EMQX 5.8.9

XMQ 0.9.18

FlashMQ 1.27.1

1M Connections

Scenario: 1M connections - 1M-Connections-5K-rate.json
Date: 2026-09-17
Client: xmq_scn 0.9.16
CPU percentages are of ONE core: 1600% = all 16 vCPU. xmq_server pins one thread per
there: the client binds 30 source addresses of 55536 ports each, which caps it at
CPU is not close to being the limit: the broker held a million at a 47% mean.
Version: 1.27.1
CPU Load: 32% mean / 95% peak
Max RAM: 4343 Mb
The same broker with one change: the session maps are sized once, from RLIMIT_NOFILE,
What that interval was: `ClientSessionManager` holds its sessions in two hash maps behind

Server	Version	CPU Load	Max RAM	Avg Connections	Avg Latency
XMQ 0.9.18	0.9.18	47% mean / 121% peak	2521 Mb	1,000,000	322us
FlashMQ 1.27.1	1.27.1	32% mean / 90% peak	4343 Mb	1,000,000	354us

XMQ 0.9.18

FlashMQ 1.27.1



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