Abstract: An in-database sharded queue for a shared-disk database is provided. First messages from at least one first enqueuer are stored on a first queue shard. The first enqueuer/s execute in a first instance of a shared-disk database system. The first shard includes a first plurality of subshards. Second messages from at least one second enqueuer are stored on a second queue shard. The second enqueuer/s execute in a second instance of the shared-disk database system. The second shard includes a second plurality of subshards. In volatile memory of the respective instances, a first message cache and a second message cache is maintained for the first shard and the second shard. The respective message caches include at least one buffer associated with the plurality of subshards.

Abstract: A method and apparatus for an in-database sharded queue that supports JMS session ordering is provided. Messages from a plurality of enqueuers are stored in a plurality of shards of a particular queue. For each enqueuer, all messages are stored in only one of the shards. Each shard includes one or more subshards, each subshard having one or more partitions of a queue table maintained by a relational database system. All messages from a first enqueuer are stored in partitions of the queue table that are assigned to a first shard of the plurality of shards. All messages from a second enqueuer are stored in partitions of the queue table that are assigned to a second shard of the plurality of shards. Subscribers of the particular queue are caused to dequeue messages from the plurality of shards.

Abstract: Handling memory pressure in an in-database sharded queue is described. Messages from a plurality of enqueuers are stored in a plurality of shards of a sharded queue. Messages from a first enqueuer are stored in a first shard. A queue table corresponding to the sharded queue is maintained. In volatile memory, a plurality of message caches is maintained, each message cache corresponding to a shard of the plurality of shards. Memory pressure is detected based on memory usage of the volatile memory. To store a specific message from the enqueuer, the specific message is stored in rows of the queue table that are assigned to the first shard. When memory pressure is not detected, the specific message is stored in a first message cache corresponding to the first shard. Subscribers of the sharded queue are caused to dequeue messages from the plurality of shards.