Consumer lag.

also: consumer lags · queue depth · queue backlog

How far a consumer is behind the newest messages, in messages or time; steadily growing lag means it can't keep up.

the two-minute refresher

Producer at 10,000 msg/s and consumer at 1,000 msg/s: lag grows by 9,000 every second.
Watch the trend: steady lag is fine, a growing one is an incident in slow motion.
Fixes: more consumers (up to the partition count), faster processing, or backpressure.
Lag in time ('5 minutes behind') is what users feel.

also: consumer lags · queue depth · queue backlog

How far a consumer is behind the newest messages, in messages or time; steadily growing lag means it can't keep up.

Producer at 10,000 msg/s and consumer at 1,000 msg/s: lag grows by 9,000 every second.
Watch the trend: steady lag is fine, a growing one is an incident in slow motion.
Fixes: more consumers (up to the partition count), faster processing, or backpressure.
Lag in time ('5 minutes behind') is what users feel.