MQTT: introduce limits for the retained message store (backport #17189) - #17190
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This adds both size and message count limits. (cherry picked from commit 6d6e90d)
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michaelklishin
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4.3.5: MQTT: introduce limits for the retained message store (backport #17189)
michaelklishin
changed the title
4.3.5: MQTT: introduce limits for the retained message store (backport #17189)
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This adds both size and message count limits to how much data can be retained via MQTT's retained messages feature. The protocol itself does not discuss any limits or safety protocols.
All retained messages flow through one code path, which is where the limits are applied.
The defaults are 100K messages (and as many topics [1]) per virtual host, or 1 GiB of data. I consider these to be very reasonable, even generous, for most MQTT workloads.
The accounting is not super precise because accounting for ETS/DETS metadata is hard but the way we compute message footprint passes the common sense check:
mc_mqtt:size/1returns the size of the topic plus message properties plus the payload, which is all we really need to account for to introduce a practical limit.This is an automatic backport of pull request MQTT: introduce limits for the retained message store #17189 done by Mergify.