Abstract: In some embodiments, a method sends first messages that request first information for a set of blocks of the blockchain to the N replicas. Each replica maintains a respective instance of the blockchain. Second messages is received from at least a portion of the N replicas. The second messages include the first information for the set of blocks from each respective instance of the blockchain that is maintained by the N replicas. The method analyzes the first information to determine whether a consensus on the first information is reached by a number of replicas. When consensus is reached, a request is sent to a replica for one or more blocks to back up to a backup blockchain and second information is received for the one or more blocks from the replica. The method uses the second information to back up the one or more blocks in the backup blockchain.

Abstract: In some embodiments, a method receives data for a block in a blockchain during a recovery process in which a recovering replica is recovering the block for a first instance of the blockchain being maintained by the recovering replica. The block is received from a second instance of the blockchain being maintained by a source replica. The method splits the data for the block into a plurality of chunks. Each chunk includes a portion of the data for the block; It is determined whether the recovering replica can recover a chunk in the plurality of chunks using a representation of the chunk. In response to determining that the recovering replica can recover the chunk, sending the representation of the chunk to the recovering replica. In response to determining that the recovering replica cannot recover the chunk, sending the data for the chunk to the recovering replica.

Abstract: In some embodiments, a method receives data for a block in a blockchain during a recovery process in which a recovering replica is recovering the block for a first instance of the blockchain being maintained by the recovering replica. The block is received from a second instance of the blockchain being maintained by a source replica. The method splits the data for the block into a plurality of chunks. Each chunk includes a portion of the data for the block; It is determined whether the recovering replica can recover a chunk in the plurality of chunks using a representation of the chunk. In response to determining that the recovering replica can recover the chunk, sending the representation of the chunk to the recovering replica. In response to determining that the recovering replica cannot recover the chunk, sending the data for the chunk to the recovering replica.

Abstract: In some embodiments, a method sends first messages that request first information for a set of blocks of the blockchain to the N replicas. Each replica maintains a respective instance of the blockchain. Second messages is received from at least a portion of the N replicas. The second messages include the first information for the set of blocks from each respective instance of the blockchain that is maintained by the N replicas. The method analyzes the first information to determine whether a consensus on the first information is reached by a number of replicas. When consensus is reached, a request is sent to a replica for one or more blocks to back up to a backup blockchain and second information is received for the one or more blocks from the replica. The method uses the second information to back up the one or more blocks in the backup blockchain.

Abstract: The present teaching relates to concurrent database operation. In one example, a plurality of requests which includes a scan request to obtain first data associated with a plurality of first keys stored in a database is received concurrently. A global version number is updated upon receipt of the scan request. The first data associated with the plurality of first keys is obtained based on the updated global version number. The first data is provided in response to the scan request.

Abstract: In one embodiment, a search engine may generate and store a plurality of search index segments such that each of the search index segments is stored in a corresponding one of a plurality of heaps of memory. The plurality of search index segments may include inverted index segments mapping content to documents containing the content. A garbage collection module may release one or more heaps of the memory.

Abstract: In one embodiment, a set of lock and unlock instructions in a read phase of a computer-readable program is replaced with a first set of tracking instructions, wherein the first set of tracking instructions track a set of locked objects identifying objects that would have been locked by executing the set of lock and unlock instructions. A second set of tracking instructions is inserted into the read phase of the computer-readable program, wherein the second set of tracking instructions track a set of read objects indicating versions of objects that are read. Validation instructions are inserted into the computer-readable program, wherein the validation instructions validate that the versions of objects in the set of read objects have not changed since they were last read and lock the set of locked objects that would have been locked upon completing execution of the set of lock and unlock instructions.

Abstract: Methods and apparatus for performing top-k query processing include pruning a list of documents to identify a subset of the list of documents, where pruning includes, for other query terms in the set of query terms, skipping a document in the list of documents based, at least in part, on the contribution of the query term to the score of the corresponding document and the term upper bound for each other query term, in the set of query terms, that matches the document.

Abstract: In one embodiment, a set of lock and unlock instructions in a read phase of a computer-readable program is replaced with a first set of tracking instructions, wherein the first set of tracking instructions track a set of locked objects identifying objects that would have been locked by executing the set of lock and unlock instructions. A second set of tracking instructions is inserted into the read phase of the computer-readable program, wherein the second set of tracking instructions track a set of read objects indicating versions of objects that are read. Validation instructions are inserted into the computer-readable program, wherein the validation instructions validate that the versions of objects in the set of read objects have not changed since they were last read and lock the set of locked objects that would have been locked upon completing execution of the set of lock and unlock instructions.

Abstract: In one embodiment, a set of lock and unlock instructions in a read phase of a computer-readable program is replaced with a first set of tracking instructions, wherein the first set of tracking instructions track a set of locked objects identifying objects that would have been locked by executing the set of lock and unlock instructions. A second set of tracking instructions is inserted into the read phase of the computer-readable program, wherein the second set of tracking instructions track a set of read objects indicating versions of objects that are read. Validation instructions are inserted into the computer-readable program, wherein the validation instructions validate that the versions of objects in the set of read objects have not changed since they were last read and lock the set of locked objects that would have been locked upon completing execution of the set of lock and unlock instructions.

Abstract: Methods and apparatus for performing top-k query processing include pruning a list of documents to identify a subset of the list of documents, where pruning includes, for other query terms in the set of query terms, skipping a document in the list of documents based, at least in part, on the contribution of the query term to the score of the corresponding document and the term upper bound for each other query term, in the set of query terms, that matches the document.

Abstract: The present teaching relates to concurrent database operation. In one example, a plurality of requests which includes a scan request to obtain first data associated with a plurality of first keys stored in a database is received concurrently. A global version number is updated upon receipt of the scan request. The first data associated with the plurality of first keys is obtained based on the updated global version number. The first data is provided in response to the scan request.

Abstract: In one embodiment, a search engine may generate and store a plurality of search index segments such that each of the search index segments is stored in a corresponding one of a plurality of heaps of memory. The plurality of search index segments may include inverted index segments mapping content to documents containing the content. A garbage collection module may release one or more heaps of the memory.

Abstract: In one embodiment, a set of lock and unlock instructions in a read phase of a computer-readable program is replaced with a first set of tracking instructions, wherein the first set of tracking instructions track a set of locked objects identifying objects that would have been locked by executing the set of lock and unlock instructions. A second set of tracking instructions is inserted into the read phase of the computer-readable program, wherein the second set of tracking instructions track a set of read objects indicating versions of objects that are read. Validation instructions are inserted into the computer-readable program, wherein the validation instructions validate that the versions of objects in the set of read objects have not changed since they were last read and lock the set of locked objects that would have been locked upon completing execution of the set of lock and unlock instructions.

Abstract: The present teaching relates to concurrency control in log-structured merge (LSM) data stores. In one example, a call is received from a thread for writing a value to a key of LSM components. A shared mode lock is set on the LSM components in response to the call. The value is written to the key once the shared mode lock is set on the LSM components. The shared mode lock is released from the LSM components after the value is written to the key.