Classic Queues Operating in "Lazy" Queue Mode (A Lazy Queue)

tip

RabbitMQ no longer supports the "lazy" mode. This page is provided for historical reference only.

Until RabbitMQ 3.12, classic queues could be configured to operate in the lazy mode, which means they would write all message to disk and wouldn't keep messages in memory at all. This setting is now ignored, although the current behaviour of classic queues is similar to what the lazy mode used to provide. The current behaviour is:

• in general, messages are written to disk, although with a delay; messages are buffered in memory briefly, until the buffer is flushed to disk
• a small subset of messages is kept in memory for fast delivery to consumers (the number of messages kept in memory depends on how quickly the consumers consume messages)
• if a message published by a producer can be immediately delivered to a consumer and the consumer acknowledges the message before the message is written to disk, it will not be written to disk (at this point the message is already delivered and acknowledged, so there is no need to write it to disk)

With older versions, you'd need to choose between low latency (non-lazy) and low-memory usage (lazy) on a per-queue basis. Current implementation provides low latency with low and stable memory usage.

The classic queues page provides further details about classic queue implementation.