Abstract: A computer implemented method is provided comprising receiving a group of transaction logs from a first database, allocating transaction logs from the group of transaction logs to a first queue and to a second queue, generating an end-of-group transaction log indicative of an end of the group of transaction logs, allocating the end-of-group log to the first queue and the second queue; replaying transaction logs from the first queue including the end-of-group transaction log allocated to the first queue, replaying transaction logs from the second queue including the end-of-group transaction log allocated to the second queue; and changing visibility of one or more transactions in response to replaying the end-of-group transaction log allocated to the first queue and the end-of-group transaction log allocated to the second queue. Related apparatus, systems, techniques and articles are also described.

Abstract: Disclosed herein are system, method, and computer program product embodiments for synchronizing lost change between a source table and a replica table. An embodiment operates by detecting a restart at a source node or a replica node. Row-ID values of replication log entries are then compared to row-ID column values of rows at a replica table of the replica node. Replication errors at a source table or the replica table are then determined based on the row-ID comparison. The rows of the source table and the replica table are then updated based on the determination.

Abstract: Disclosed herein are system, method, and computer program product embodiments for removing a deadlock during replication from distributed source tables to a replica node. An embodiment operates by detecting a deadlock at a parallel log replayer at a replica node. A first replication log entry from a queue at the parallel log replayer is then selected based on whether removing the first replication log entry from the queue removes the deadlock. The first replication log entry is then forwarded to a waiting queue. A second replication log entry is then replayed at the parallel log replayer. After replaying the second replication log entry, the first replication log entry is replayed at the parallel log replayer.

Abstract: Disclosed herein are system, method, and computer program product embodiments for replicating a database transaction to a replica table. An embodiment operates by receiving a replication log entry and an associated transaction commit log entry for a database transaction to be replayed to a row at a replica table. A row-ID value of the replication log entry is compared to a row-ID column value of the row at the replica table. The replication log entry is then replayed at a parallel log replayer based on the comparison. The database transaction is then committed to the replica table by replaying the associated transaction commit log entry at a transaction log replayer.

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: A transaction management service layer monitors a plurality of read and write transactions being executed by the data engines by way of client libraries at each of a plurality of data engines. In addition, the transaction management server layer maintains and coordinates transaction timestamp and sequence numbers that are shared by the plurality of data engines. The transaction management service layer identifies and resolves conflicts among the plurality of transactions. The transaction management service layer is a separate and independent service that is isolated from other components of the plurality of data engines. Related apparatus, systems, techniques and articles are also described.

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 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 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 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: Methods, systems and computer-readable storage mediums encoded with computer programs executed by one or more processors for providing a compressed representation of a transaction token are disclosed. In an embodiment, a transaction token maintains statues of transaction to a database in a first data structure and a second data structure. The first data structure includes a plurality of identifiers respectively corresponding to the transactions to the database and a corresponding status of each identifier indicating whether a given transaction is open or closed, wherein the plurality of identifiers is maintained below a threshold number of identifiers. The second data structure includes a plurality of identifiers of transactions to the database beyond the threshold and whose status is open.

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 of data within a database environment having a source node and a replica node. The source node executes a database operation on at least one database table stored by the source node. The source node asynchronously sends the database operation to the replica node. A prepare commit request is synchronously sent from the source node to the replica node. The source node receives a synchronous precommit acknowledgement from the replica node. The precommit acknowledgement indicates that the database operation was executed at the replica node. The source node commits a transaction associated with the database operation.

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 coordinator node receives local transaction tokens from the first and the at least a second worker nodes. The coordinator nodes determines a synchronized transaction token using at least the local transaction tokens from the first and the at least a second worker nodes. The coordinator node sends the synchronized transaction token to the first and the at least a second worker nodes.

Abstract: Methods, systems and computer-readable storage mediums encoded with computer programs executed by one or more processors for providing a compressed representation of a transaction token are disclosed. In an embodiment, upon a receipt of a request for a write transaction at a slave server it is determined whether there exists an unassigned transaction identifier (TID) stored locally at the slave server as provided by a master server to the slave server prior to the receipt of the write request by the slave server. If there exists an unassigned TID at the slave server, the slave server is configured to assign the unassigned TID to the write transaction, otherwise the slave server is configured to request a plurality of unassigned TIDs from the master server, receive the plurality of unassigned TIDs, and assign one of the received unassigned TIDs to the write transaction. The write transaction is processed.

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 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 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 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.