Abstract: A plurality of database modification statements are received as part of a database transaction that implicates data stored within a database. Thereafter, lock requests are initiated that requesting the database to lock the implicated data. At least one database operation by at least one of the database modification statements is then executed prior to receiving responses from at least a portion of the lock requests. After confirming that prior lock requests made by the transaction are successfully processed, a commit to make changes to the corresponding implicated data permanent is initiated. The implicated data can then be caused to be unlocked after the commit completes. Related apparatus, systems, techniques and articles are also described.

Abstract: Technologies are provided for reducing or eliminating transaction consistency anomalies that can occur during data replication, such as during database table replication. For example, commit values can be used to coordinate requests so that the requests are not performed on database tables with inconsistent data.

Abstract: Technologies are described for performing synchronization within a database environment. A source host stores multiple database tables and a replica host stores copies of the multiple database tables. During synchronization, replication log replay is blocked at the replica node, and a multithreaded process locks the multiple database tables of the source hosts, reactivates replication log generation for each of the multiple database tables, and then unlocks the database tables. A synchronization timestamp is acquired and used to synchronize the multiple database tables with the copies of the multiple database tables. After synchronization, replication log replay is reactivated at the replica host for the copies of the multiple database tables.

Abstract: Technologies for performing garbage collection in database systems, such as multi-version concurrency control (MVCC) database systems, are described. For example, different garbage collection techniques can be used separately or in various combinations, including interval garbage collection, group garbage collection, table garbage collection, and combinations. For example, a particular type of combination, called hybrid garbage collection, uses technique from interval garbage collection and group garbage collection, or from interval, group, and table garbage collection.

Abstract: Technologies are described for facilitating replay of requests for database operations. A plurality of requests for database operations are received. Each of the plurality of requests includes a type, an access unit identifier, and a chronological identifier. Execution dependencies are determined between the plurality of requests based on the type, access unit identifier, and chronological identifier of each of the plurality of requests. The execution dependencies are stored.

Abstract: Technologies are described for facilitating transaction processing within a database environment having a coordinator node, a first worker node, and at least a second worker node. The first worker node sends a request from to the coordinator node for at least a first synchronization token maintained by the coordinator node. The first worker node receives the at least a first synchronization token from the coordinator node. The first worker node assigns the at least a first synchronization token to a snapshot as a snapshot ID value. The snapshot is executed at the first worker node. The first worker node forwards the snapshot ID value to the at least a second worker node.

Abstract: Technologies for performing garbage collection in database systems, such as multi-version concurrency control (MVCC) database systems, are described. For example, different garbage collection techniques can be used separately or in various combinations, including interval garbage collection, group garbage collection, table garbage collection, and combinations. For example, a particular type of combination, called hybrid garbage collection, uses technique from interval garbage collection and group garbage collection, or from interval, group, and table garbage collection.

Abstract: Technologies are provided for reducing or eliminating transaction consistency anomalies that can occur during data replication, such as during database table replication. For example, commit values can be used to coordinate requests so that the requests are not performed on database tables with inconsistent data.

Abstract: Technologies are described for performing synchronization within a database environment. A source host stores multiple database tables and a replica host stores copies of the multiple database tables. During synchronization, replication log replay is blocked at the replica node, and a multithreaded process locks the multiple database tables of the source hosts, reactivates replication log generation for each of the multiple database tables, and then unlocks the database tables. A synchronization timestamp is acquired and used to synchronize the multiple database tables with the copies of the multiple database tables. After synchronization, replication log replay is reactivated at the replica host for the copies of the multiple database tables.

Abstract: Technologies are described for facilitating replay of requests for database operations. A plurality of requests for database operations are received. Each of the plurality of requests includes a type, an access unit identifier, and a chronological identifier. Execution dependencies are determined between the plurality of requests based on the type, access unit identifier, and chronological identifier of each of the plurality of requests. The execution dependencies are stored.

Abstract: Technologies are described for facilitating transaction processing within a database environment having a coordinator node, a first worker node, and at least a second worker node. The first worker node sends a request from to the coordinator node for at least a first synchronization token maintained by the coordinator node. The first worker node receives the at least a first synchronization token from the coordinator node. The first worker node assigns the at least a first synchronization token to a snapshot as a snapshot ID value. The snapshot is executed at the first worker node. The first worker node forwards the snapshot ID value to the at least a second worker node.

Abstract: Technologies are described for facilitating transaction processing within a database environment having first, second, and third database system nodes. In the database system, the first database system node receives from the second database system node a request to precommit a first database transaction. The first database system node stores information for the first database transaction that includes an indication that the second database system node coordinates the committing of the first database transaction. The first database system node receives from the third database system node a request to precommit a second database transaction. The first database system node stores information for the second database transaction that includes an indication that the third database system node coordinates the committing of the second database transaction.

Abstract: Technologies are described for performing replication within a database environment. Where a database transaction is replicated at multiple replica nodes, a replica node is selected as a coordinator replica node for the transaction. The other replica node or nodes are designated as follower replica nodes for the transaction. A follower replica node sends the coordinator replica node a precommit notification when the follower replica node has precommitted the transaction. The coordinator replica node sends the follower replica node a postcommit notification to commit the transaction when the transaction has been precommitted by all of the replica nodes to which the transaction is to be replicated.

Abstract: Technologies are described for performing replication within a database environment. Where database operations are carried out at multiple source nodes, the operations can be ordered by the source node on which they were executable prior to being replayed at a replica node. In addition, the operations can be precommitted, so that the operations can be reviewed by a replayer at the replica node before the transaction containing the operations has been fully committed.

Abstract: Technologies are described for facilitating the processing of requests for database operations in a distributed database environment. Criteria are defined for processing a request for a database operation according to first or second snapshot isolation protocols. A request for a database operation is received and it is determined if the snapshot isolation protocol criteria are met. If the criteria are met, the request can be processed using a local snapshot identifier value of a worker node. If the criteria are not met, the local snapshot identifier value is synchronized with another node, and the request processed using the updated snapshot identifier value.

Abstract: Technologies are described for facilitating transaction processing in a distributed database environment. A database client sends database operations to a slave node, which mediates execution of the transaction. A connection between the database client and the slave node is associated with an identifier, and the transaction has an identifier. The database client sends a commit request to a master node over a network connection between the master node and the database client. The commit request includes the transaction identifier. The commit request can also include an indication of database nodes executing operations in the transaction.

Abstract: An oldest version timestamp is received from a first database. A current commit timestamp is received from a second database configured to asynchronously replicate the first database. The current global commit timestamp corresponds to a commit transaction executed in the first database and subsequently replicated in the second database. A first test query is then issued to the second database including a request for a current timestamp of the second database. A second test query is issued to the primary database requesting records associated with a target update version that has a target timestamp equal to the current snapshot timestamp. A determination is then made that a first return associated with the first test query and a second return associated with the second test query are identical indicating a successful validation. Related apparatus, systems, techniques and articles are also described.

Abstract: Technologies for performing garbage collection in database systems, such as multi-version concurrency control (MVCC) database systems, are described. For example, different garbage collection techniques can be used separately or in various combinations, including interval garbage collection, group garbage collection, table garbage collection, and combinations. For example, a particular type of combination, called hybrid garbage collection, uses technique from interval garbage collection and group garbage collection, or from interval, group, and table garbage collection.

Abstract: Technologies are described for performing replication within a database environment. Where a database transaction is replicated at multiple replica nodes, a replica node is selected as a coordinator replica node for the transaction. The other replica node or nodes are designated as follower replica nodes for the transaction. A follower replica node sends the coordinator replica node a precommit notification when the follower replica node has precommitted the transaction. The coordinator replica node sends the follower replica node a postcommit notification to commit the transaction when the transaction has been precommitted by all of the replica nodes to which the transaction is to be replicated.

Abstract: Technologies are described for facilitating database system recovery in a distributed database environment having a master node and at least one slave node. The master node maintains an in-memory reference that includes transaction identifiers and their corresponding commit identifiers. When a slave node requests that a commit identifier be assigned to a transaction, the transaction and commit identifiers for the transaction are added to the in-memory reference. The commit identifier is sent by the master node to the slave node. The slave node writes a log entry to a commit log that includes the transaction identifier and the assigned commit identifier. If the database system is interrupted before the slave node writes the commit log entry, the slave node can request the commit identifier for the transaction from the master node, which retrieves the identifier from the in-memory reference.