Handling memory pressure in an in-database sharded queue

A method comprising:

• storing messages from a plurality of enqueuers in a plurality of shards of a sharded queue in a shared-disk database system;
• maintaining, by the shared-disk database system, a queue table corresponding to the sharded queue;
• maintaining, in volatile memory of database instances of the shared-disk database system, a plurality of message caches, each message cache corresponding to a shard of the plurality of shards;
• wherein the plurality of enqueuers comprises at least one first enqueuer, wherein messages from the at least one first enqueuer are enqueued in the first shard;
• determining whether the first shard is currently cached or uncached based on whether memory pressure is detected in a first instance of the shared-disk database, wherein the first instance has enqueue ownership of the first shard;
• wherein storing a specific message from the first enqueuer comprises:
• storing the specific message in a row of the queue table in a partition assigned to the first shard;
• when the first shard is cached, storing the specific message in a first message cache of the plurality of message caches, the first message cache corresponding to the first shard;
• when the first shard is uncached, storing message metadata corresponding to the specific message in the first message cache;
• wherein the method is performed by one or more computing devices.

A non-transitory computer-readable medium storing instructions which, when executed by one or more processors, cause the one or more processors to carry out the steps of:

• storing messages from a plurality of enqueuers in a plurality of shards of a sharded queue;
• wherein the plurality of enqueuers comprises a first enqueuer, wherein messages from the first enqueuer are stored in the first shard;
• maintaining, in a relational database system, a queue table corresponding to the sharded queue;
• maintaining, in volatile memory, a plurality of message caches, each message cache corresponding to a shard of the plurality of shards;
• detecting memory pressure based on memory usage of the volatile memory;
• wherein storing a specific message from the first enqueuer comprises:
• storing the specific message in rows of the queue table that are assigned to the first shard;
• when memory pressure is not detected, storing the specific message in a first message cache of the plurality of message caches, the first message cache corresponding to the first shard;
• causing subscribers of the sharded queue to dequeue messages from the plurality of shards;
• wherein the method is performed by one or more computing devices.

A non-transitory computer-readable medium storing instructions which, when executed by one or more processors, cause the one or more processors to carry out the steps of:

• storing messages from a plurality of enqueuers in a plurality of shards of a sharded queue in a shared-disk database system;
• maintaining, by the shared-disk database system, a queue table corresponding to the sharded queue;
• maintaining, in volatile memory of database instances of the shared-disk database system, a plurality of message caches, each message cache corresponding to a shard of the plurality of shards;
• wherein the plurality of enqueuers comprises at least one first enqueuer, wherein messages from the at least one first enqueuer are enqueued the first shard;
• determining whether the first shard is currently cached or uncached based on whether memory pressure is detected in a first instance of the shared-disk database, wherein the first instance has enqueue ownership of the first shard;
• wherein storing a specific message from the first enqueuer comprises:
• storing the specific message in a row of the queue table in a partition assigned to the first shard;
• when the first shard is cached, storing the specific message in a first message cache of the plurality of message caches, the first message cache corresponding to the first shard;
• when the first shard is uncached, storing message metadata corresponding to the specific message in the first message cache;
• wherein the method is performed by one or more computing devices.