Lightning Memory-Mapped Database: Difference between revisions

Revision as of 12:26, 26 May 2021

Revision as of 13:37, 26 May 2021

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=== Concurrency ===

LMDB employs [[multiversion concurrency control]] (MVCC) and allows multiple threads within multiple processes to coordinate simultaneous access to a database. Readers scale linearly by design. While write transactions are globally serialized via a [[mutex]], read-only transactions operate in parallel, including in the presence of a write transaction, and are entirely [[wait free]] except for the first read-only transaction on a thread. Each thread reading from a database gains ownership of an element in a shared memory array, which it may update to indicate when it is within a transaction. Writers scan the array to determine the oldest database version the transaction must preserve, without requiring direct synchronization with active readers.{{cn|reason=whole<ref>[http://www.lmdb.tech/bench/inmem/scaling.html sectionscaling hasbenchmarks nofor references,LMDB]</ref><ref>[http://www.lmdb.tech/bench/inmem/scale2/ anomalousin-memory forbenchmark thescaling page as afor whole}}LMDB</ref>

== Performance ==