| 摘要 |
An in-memory database system uses a shared memory to cache records and keys read from a database and controls the updating of the records and keys through a database manager process. When a transaction performs an update, the original, unmodified data is preserved in the shared memory, the new data is written to the shared memory, and a look-aside table for the transaction records the changes. A transaction performs read-only access to the shared memory using its own context while a versioning scheme based on the look-aside tables ensures a read-committed isolation level view of the original, unmodified data until the modifying transaction commits the update. The database manager is responsible for writing the new data into the shared memory and for maintaining the look-aside tables for all transaction which have made modifications to the data in the shared memory. The database manager also writes committed changes to the database and performs rollback on uncommitted changes in the shared memory using the entries in the look-aside table for the committing/aborting transaction. The shared memory is divided into logical pages and short duration page latches are employed to maintain consistency on the page while a transaction or the database manager is reading or writing data on the page.
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