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Hekaton (also known as SQL Server In-Memory OLTP) is the project code name for an upcoming high performance In-memory Database for OLTP workloads built into Microsoft SQL Server. Traditional RDBMS architecture was designed when memory resources were expensive, and was optimized for disk I/O. Modern hardware has much more memory, which affects database design principles dramatically. Modern design can now optimize for a working set stored entirely in main memory. Hekaton fully provides ACID database properties.
In addition to memory optimization, Hekaton design also considers additional HW trends—such as multi-core processors and stalling CPU clock rate. Hekaton is built with Microsoft research support and is fundamentally different from the obsolescent "DBCC PINTABLE" feature in earlier SQL Server versions.
In a nutshell – In-memory OLTP is a new database engine optimized for memory resident data and OLTP workloads. In-memory OLTP is fully integrated into SQL Server – not a separate system. To take advantage of In-memory OLTP, a user defines a heavily accessed table as memory optimized. In-memory OLTP tables are fully transactional, durable and accessed using T-SQL in the same way as regular SQL Server tables. A query can reference both In-memory OLTP tables and regular tables, and a transaction can update data in both types of tables. Expensive T-SQL stored procedures that reference only In-memory OLTP tables can be natively compiled into machine code for further performance improvements. The engine is designed for extremely high session concurrency for OLTP type of transactions driven from a highly scaled-out mid-tier. To achieve this it uses latch-free data structures and a new optimistic, multi-version concurrency control technique. The end result is a selective and incremental migration into In-memory OLTP to provide predictable sub-millisecond low latency and high throughput with linear scaling for DB transactions. The actual performance gain depends on many factors but we have typically seen 5X-20X in customer workloads.
This SQL Server In-memory OLTP capability will be released in SQL 2014 version. The Data Warehousing In-memory technology is also available - as in the Columnstore technology.
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