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‎docs/database-engine/configure-windows/hybrid-buffer-pool.md‎

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The hybrid buffer pool feature is available for both Windows and Linux. The PMEM device must be formatted with a filesystem that supports DAX (DirectAccess). XFS, EXT4, and NTFS file systems all have support for DAX. SQL Server will automatically detect if data files reside on an appropriately formatted PMEM device and perform memory mapping of database files upon startup, when a new database is attached, restored, or created.
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For more on Windows Server support for PMEM, also referred to as Storage Class Memory (SCM) see [deploy persistent memory on Windows Server](/windows-server/storage/storage-spaces/deploy-pmem/).
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For more information, see:
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For more on configuring SQL Server on Linux for PMEM devices see [persistent memory configuration for Linux](../../linux/sql-server-linux-configure-pmem.md).
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* [Understand and deploy persistent memory (Windows)](/windows-server/storage/storage-spaces/deploy-pmem/)
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* [Configure persistent memory (PMEM) for SQL Server on Linux](../../linux/sql-server-linux-configure-pmem.md)
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## Enable hybrid buffer pool
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ALTER SERVER CONFIGURATION SET MEMORY_OPTIMIZED HYBRID_BUFFER_POOL = OFF;
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```
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By default, hybrid buffer pool is disabled at the instance level. In order for this change to take effect, the instance must be restarted. This is to ensure a sufficient number of hash page are allocated for the buffer pool, as PMEM capacity on the server now needs to be accounted for.
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By default, hybrid buffer pool is disabled at the instance level. In order for this change to take effect, the instance must be restarted. This ensures enough hash pages are allocated for the buffer pool, as PMEM capacity on the server now needs to be accounted for.
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The following example disables hybrid buffer pool for a specific database.
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‎docs/linux/sql-server-linux-configure-pmem.md‎

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---
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title: Configure persistent memory (PMEM) for SQL Server on Linux
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title: Configure persistent memory (PMEM)
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description: This article provides a walk-through for configuring PMEM on Linux.
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ms.custom: seo-lt-2019
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author: briancarrig
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ms.technology: linux
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monikerRange: ">= sql-server-linux-ver15 || >= sql-server-ver15 || = sqlallproducts-allversions"
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---
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# How to configure persistent memory (PMEM) for SQL Server on Linux
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# Configure persistent memory (PMEM) for SQL Server on Linux
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[!INCLUDE[appliesto-ss-xxxx-xxxx-xxx-md-linuxonly](../includes/appliesto-ss-xxxx-xxxx-xxx-md-linuxonly.md)]
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Once the device has been configured with `ndctl`, created, and mounted, you can place database files in it or create a new database.
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PMEM devices are O_DIRECT (direct I/O) safe, you can consider enabling trace flag 3979 to disable the forced flush mechanism. For more information see [FUA support](https://support.microsoft.com/help/4131496/enable-forced-flush-mechanism-in-sql-server-2017-on-linux). Forced unit access internals are covered here [FUA internals](https://blogs.msdn.microsoft.com/bobsql/2018/12/18/sql-server-on-linux-forced-unit-access-fua-internals/).
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Because PMEM devices are O_DIRECT (direct I/O) safe, consider enabling trace flag 3979 to disable the forced flush mechanism. For more information see [FUA support](https://support.microsoft.com/help/4131496/enable-forced-flush-mechanism-in-sql-server-2017-on-linux). Forced unit access internals are covered here [FUA internals](https://blogs.msdn.microsoft.com/bobsql/2018/12/18/sql-server-on-linux-forced-unit-access-fua-internals/).
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## Next steps
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docs/relational-databases/databases/add-persisted-log-buffer-to-a-database.md renamed to docs/relational-databases/databases/add-persisted-log-buffer.md

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---
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title: "Add Persisted Log Buffer to a Database | Microsoft Docs"
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title: "Add persisted log buffer to a database"
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ms.custom: ""
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ms.date: "10/30/2019"
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ms.prod: sql
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ms.author: "brcarrig"
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manager: amitban
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---
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# Add Persisted Log Buffer to a Database
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# Add persisted log buffer to a database
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[!INCLUDE[appliesto-ss-xxxx-xxxx-xxx-md](../../includes/appliesto-ss-xxxx-xxxx-xxx-md.md)]
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This topic describes how to add a Persisted Log Buffer to a database in [!INCLUDE[sqlv15](../../includes/sssqlv15-md.md)] using [!INCLUDE[tsql](../../includes/tsql-md.md)].
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This topic describes how to add a persisted log buffer to a database in [!INCLUDE[sqlv15](../../includes/sssqlv15-md.md)] using [!INCLUDE[tsql](../../includes/tsql-md.md)].
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## Permissions
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Requires ALTER permission on the database.
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## Configure persistent memory device (Linux)
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To configure a persistent memory device in [Linux](../../linux/sql-server-linux-configure-pmem.md)).
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To configure a persistent memory device in [Linux](../../linux/sql-server-linux-configure-pmem.md).
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## Configure persistent memory device (Windows)
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To configure a persistent memory device in [Windows](/windows-server/storage/storage-spaces/deploy-pmem/).
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## Add a persisted log buffer to a database
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```ALTER DATABASE <MyDB> ADD LOG FILE (NAME = <DAXlog>, FILENAME = '<Filepath to DAX Log File>', SIZE = 20MB);```
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The following examples adds a persisted log buffer.
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```sql
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ALTER DATABASE <MyDB>
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ADD LOG FILE
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(
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NAME = <DAXlog>,
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FILENAME = '<Filepath to DAX Log File>',
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SIZE = 20MB
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);
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```
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The volume or mount the new log file is placed must be formatted with DAX (NTFS) or mounted with the DAX option (XFS/EXT4).
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## Remove a persisted log buffer
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`ALTER DATABASE <MyDB> SET SINGLE_USER;`
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`ALTER DATABASE <MyDB> REMOVE FILE <DAXlog>;`
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`ALTER DATABASE <MyDB> SET MULTI_USER;`
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To safely remove a persisted log buffer, the database must be placed in single user mode in order to drain the persisted log buffer.
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The following example places removes a persisted log buffer.
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Database must be placed in single user mode in order to drain the persisted log buffer and be able to remove it safely.
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```sql
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ALTER DATABASE <MyDB> SET SINGLE_USER;
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ALTER DATABASE <MyDB> REMOVE FILE <DAXlog>;
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ALTER DATABASE <MyDB> SET MULTI_USER;
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```
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## Limitations
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Normal restore conditions apply. If persisted log buffer is restored to a DAX volume or mount, it will continue to function, otherwise it can be safely removed.
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## See Also
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## Next steps
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- [How It Works (It Just Runs Faster): Non-Volatile Memory SQL Server Tail Of Log Caching on NVDIMM](https://blogs.msdn.microsoft.com/bobsql/2016/11/08/how-it-works-it-just-runs-faster-non-volatile-memory-sql-server-tail-of-log-caching-on-nvdimm/)
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- [Data exposed: Latency and Durability with SQL Server 2016](https://channel9.msdn.com/Shows/Data-Exposed/Latency-and-Durability-with-SQL-Server-2016)

‎docs/relational-databases/in-memory-database.md‎

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title: "In-Memory Database Systems Features and Technologies | Microsoft Docs"
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title: "In-memory database systems features and technologies"
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ms.date: 10/30/2019
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ms.prod: sql
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# In-Memory Database Systems and Technologies
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# In-memory database systems and technologies
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[!INCLUDE[appliesto-ss-xxxx-xxxx-xxx-md](../includes/appliesto-ss-xxxx-xxxx-xxx-md.md)]
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The fast volatile cache that fronts a considerably slower but durable media - this dynamic has been predominant for relational database workloads for decades and necessitates particular approaches to workload management. The opportunities presented by faster memory transfer rates, greater capacity, or even persistent memory will facilitate the development of new features and technologies that can spur new approaches to relational database workload management. As we develop new in-memory based approaches, we will list the technologies or features underpinning them here on this reference page.
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## Hybrid Buffer Pool
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## Hybrid buffer pool
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[!INCLUDE[appliesto-ss-xxxx-xxxx-xxx-md](../includes/appliesto-ss-xxxx-xxxx-xxx-md.md)]
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[Hybrid Buffer Pool](../database-engine/configure-windows/hybrid-buffer-pool.md) expands the buffer pool for database files residing on byte-addressable persistent memory storage devices for both Windows and Linux platforms with [!INCLUDE[sql-server-2019](../includes/sssqlv15-md.md)].
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[Hybrid buffer pool](../database-engine/configure-windows/hybrid-buffer-pool.md) expands the buffer pool for database files residing on byte-addressable persistent memory storage devices for both Windows and Linux platforms with [!INCLUDE[sql-server-2019](../includes/sssqlv15-md.md)].
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## Memory-Optimized TempDB Metadata
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## Memory-optimized `tempdb` metadata
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[!INCLUDE[appliesto-ss-xxxx-xxxx-xxx-md](../includes/appliesto-ss-xxxx-xxxx-xxx-md.md)]
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[!INCLUDE[sql-server-2019](../includes/sssqlv15-md.md)] introduces a new feature that is [memory-optimized tempdb metadata](./databases/tempdb-database.md#memory-optimized-tempdb-metadata), which effectively removes some contention bottlenecks and unlocks a new level of scalability for tempdb-heavy workloads.
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## In-Memory OLTP
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## In-memory OLTP
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[!INCLUDE[appliesto-ss-xxxx-xxxx-xxx-md](../includes/appliesto-ss-xxxx-xxxx-xxx-md.md)]
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[In-Memory OLTP](./in-memory-oltp/in-memory-oltp-in-memory-optimization.md) is a database technology available in [!INCLUDE[ssNoVersion](../includes/ssnoversion-md.md)] and [!INCLUDE[ssSDS](../includes/sssds-md.md)] for optimizing performance of transaction processing, data ingestion, data load, and transient data scenarios.
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**Applies to:** [!INCLUDE[ssSQL14](../includes/sssql14-md.md)] to [!INCLUDE[ssNoVersion](../includes/ssnoversion-md.md)].
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[In-memory OLTP](./in-memory-oltp/in-memory-oltp-in-memory-optimization.md) is a database technology available in [!INCLUDE[ssNoVersion](../includes/ssnoversion-md.md)] and [!INCLUDE[ssSDS](../includes/sssds-md.md)] for optimizing performance of transaction processing, data ingestion, data load, and transient data scenarios.
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## Configuring persistent memory support for Linux
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[!INCLUDE[appliesto-ss-xxxx-xxxx-xxx-md-linuxonly](../includes/appliesto-ss-xxxx-xxxx-xxx-md-linuxonly.md)]
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[!INCLUDE[sqlv15](../includes/sssqlv15-md.md)] describes how to configure persistent memory (PMEM) using the `ndctl` utility [persistent memory](../linux/sql-server-linux-configure-pmem.md).
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## Persisted Log Buffer
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## Persisted log Buffer
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Service Pack 1 of [!INCLUDE[ssSQL16](../includes/sssql16-md.md)] introduced a performance optimization for write intensive workloads that were bound by WRITELOG waits. Persistent memory is used to store the log buffer. This buffer, which is small (20 MB per user database), has to be flushed to disk in order for the transactions written to the transaction log to be hardened. For write intensive OLTP workloads, this flushing mechanism can become a bottleneck. With the log buffer on persistent memory, the number of operations required to harden the log is reduced, improving overall transaction times and increasing workload performance. This process was introduced as [Tail of Log Caching]( https://blogs.msdn.microsoft.com/bobsql/2016/11/08/how-it-works-it-just-runs-faster-non-volatile-memory-sql-server-tail-of-log-caching-on-nvdimm/). However, there was a perceived conflict with [Tail Log Backups](./backup-restore/tail-log-backups-sql-server.md) and the traditional understanding that the tail of the log was the portion of the transaction log hardened but not yet backed up. Since the official feature name is Persisted Log Buffer, this is the name used here.
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For steps to create a Persisted Log Buffer, see [here](./databases/add-persisted-log-buffer-to-a-database.md).
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**Applies to:** [!INCLUDE[sqlv15](../includes/sssqlv15-md.md)] to [!INCLUDE[ssNoVersion](../includes/ssnoversion-md.md)].
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See [Add persisted log buffer to a database](./databases/add-persisted-log-buffer.md).

‎docs/toc.yml‎

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href: relational-databases/in-memory-database.md
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- name: Hybrid Buffer Pool
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href: database-engine/configure-windows/hybrid-buffer-pool.md
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- name: Add persisted log buffer
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href: relational-databases/databases/add-persisted-log-buffer.md
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- name: Change Server Authentication Mode
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href: database-engine/configure-windows/change-server-authentication-mode.md
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- name: SQL Writer Service

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