Abstract: Systems and methods are provided for efficiently maintaining a transaction sequence witness service to ensure that requests to read data provide consistent results across all storage nodes in a distributed system. When a storage node receives a request for a data object, the node may obtain—from transaction sequence witness service—the latest sequence number associated with the object. If the sequence number indicates the object has been modified in the period of time since the currently stored version was stored, the node can obtain the current version from persistent storage.

Abstract: Systems and methods are provided for managing the order of data written to a transaction log in a distributed storage system. In a system with multiple nodes, if sequencers are naively generated without taking into consideration inconsistencies among the different nodes generating the sequencers, then the sequencers may not increase for each data transaction. To alleviate this problem, the node committing the transaction to the transaction log may perform a consistent read and verifies that the sequencer advances. If the sequencer does not advance, the node can perform a context-dependent operation such as adjusting the sequencer, acknowledging the write without committing it to the transaction log, or rejecting the write altogether.

Abstract: Systems and methods are provided for using a distributed cache architecture with different methods to load balance requests depending upon whether a requested data item is a freely-requested item (e.g., a “hot key”). The cache may be implemented as a consistent hash ring, and most keys may be assigned to particular node based on a consistent hash. For hot key requests, the requests may be distributed among a subset of nodes rather than being assigned to a specific node using consistent hashing. When a witness service is used to ensure that cached data is fresh, verification requests for data regarding hot keys may be batched to avoid overloading the witness service with hot key requests.

Abstract: Unstructured data items are stored in an item collection. An access request comprising an input interpretation rule and a filtering criterion is directed to at least a portion of the item collection. Records are extracted from an unstructured data item using the input interpretation rule. A response to the access request is obtained, based at least partly in a determination that one of the records satisfies the filtering criterion.

Abstract: Unstructured data items are stored at an object storage service. A filtering criterion to be used to generate a result set for an access request is determined. A test that can be used to determine, without completing parsing of a record identified in an unstructured data item, whether the record satisfies the filtering criterion is identified. Parsing of a particular record is abandoned in response to determining, using the test, that the record satisfies the filtering criterion. A response to the access request is determined using a subset of records that satisfy the filtering criterion.