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Use the `availability group commit time` server configuration option to specify the group commit time, in milliseconds, for an [Always On availability group replica](../../database-engine/availability-groups/windows/overview-of-always-on-availability-groups-sql-server.md).
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Use the `availability group commit time` server configuration option to specify the group commit time, in milliseconds, for an [Always On availability group](../availability-groups/windows/overview-of-always-on-availability-groups-sql-server.md).
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> [!NOTE]
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> The `availability group commit time` server configuration option is available starting with [!INCLUDE [sssql25-md](../../includes/sssql25-md.md)].
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## Overview
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Changes made inside a transaction aren't visible outside of the transaction until the transaction is committed. The definition of a committed transaction for an Always On availability group involves all synchronous secondary replicas in the availability group acknowledging the hardened commit. After a commit is issued on the primary replica, that fact needs to be propagated quickly across the network to all secondary replicas.
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Changes made inside a transaction aren't visible outside of the transaction until the transaction is committed. The definition of a committed transaction for an Always On availability group involves all synchronous secondary replicas in the availability group acknowledging the hardened commit. After a commit is issued on the primary replica, that fact needs to be propagated quickly across the network to all secondary replicas.
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Since SQL Server relies on [write-ahead transaction logging](../../relational-databases/sql-server-transaction-log-architecture-and-management-guide.md#WAL) to maintain ACID properties of a transaction, changes are first recorded to the transaction log in the form of [log blocks](../../relational-databases/sql-server-transaction-log-architecture-and-management-guide.md#log-blocks). These log blocks are sent, and then applied, to the transaction log of all the secondary replicas.
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@@ -41,9 +41,9 @@ For business scenarios where the default value of 10 milliseconds is too long, y
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- The default value of `0` indicates that [!INCLUDE [ssNoVersion](../../includes/ssnoversion-md.md)] uses the default value of 10 ms for the availability group commit time.
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- The `availability group commit time` server configuration option is available when [show advanced options](../../database-engine/configure-windows/show-advanced-options-server-configuration-option.md) is set to `1`.
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- The `availability group commit time` server configuration option is available when [show advanced options](show-advanced-options-server-configuration-option.md) is set to `1`.
description: Find out about the backup checksum default option. See how to use it to turn backup checksum on or off during SQL Server backup and restore operations.
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author: rwestMSFT
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ms.author: randolphwest
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ms.date: 03/28/2024
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ms.date: 08/26/2025
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ms.service: sql
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ms.subservice: configuration
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ms.topic: how-to
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---
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# Configure the backup checksum default (server configuration option)
Use the backup checksum default setting to enable or disable backup checksum during all backup and restore operations at the instance level.
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Use the `backup checksum default` setting to enable or disable backup checksum during all backup and restore operations at the instance level.
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To configure checking for errors for individual backup or restore operations, see [Enable or disable backup checksums during backup or restore (SQL Server)](../../relational-databases/backup-restore/enable-or-disable-backup-checksums-during-backup-or-restore-sql-server.md).
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To enable backup checksum for all backup and restore operations at the instance level, run the following command:
You can use the backup checksum default setting to provide error-management options (`CHECKSUM` and `NO_CHECKSUM`) when using backup applications or utilities that don't natively expose these options. You might also use this option when you use utilities such as [!INCLUDE [ssnoversion-md](../../includes/ssnoversion-md.md)] log shipping or the Backup database task from [!INCLUDE [ssnoversion-md](../../includes/ssnoversion-md.md)] maintenance plans. These utilities and the associated Transact-SQL stored procedures don't provide an option to include the `CHECKSUM` option during backup.
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You can use the `backup checksum default` setting to provide error-management options (`CHECKSUM` and `NO_CHECKSUM`) when using backup applications or utilities that don't natively expose these options. You might also use this option when you use utilities such as [!INCLUDE [ssnoversion-md](../../includes/ssnoversion-md.md)] log shipping or the Backup database task from [!INCLUDE [ssnoversion-md](../../includes/ssnoversion-md.md)] maintenance plans. These utilities and the associated Transact-SQL stored procedures don't provide an option to include the `CHECKSUM` option during backup.
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## More information
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If the page checksum validation fails during the backup operation, [!INCLUDE [ssnoversion-md](../../includes/ssnoversion-md.md)] stops the backup operation and reports error message 3043. For more information on the error and troubleshooting steps, see the error page for [MSSQLSERVER_3043](../../relational-databases/errors-events/mssqlserver-3043-database-engine-error.md).
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When you use the explicit `NO_CHECKSUM` option in the `BACKUP` command, the backup checksum default server option is overridden.
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When you use the explicit `NO_CHECKSUM` option in the `BACKUP` command, the `backup checksum default` server option is overridden.
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To determine whether checksum was being used during a backup to protect a backup set, use one of the following methods:
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- The `HasBackupChecksums` flag in the output of the `RESTORE HEADERONLY` command. For example:
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```sql
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RESTORE headeronlyFROMdisk='c:\temp\master.bak'
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RESTORE HEADERONLYFROMDISK='c:\temp\master.bak';
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```
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- The `has_backup_checksums` column in the `backupset` system table in the `msdb` database. For example:
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```sql
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SELECT has_backup_checksums, database_name, *
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FROM msdb..backupset
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SELECT has_backup_checksums,
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database_name,
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*
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FROM msdb..backupset;
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```
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If the backup is performed by using the `CHECKSUM` option, the restore operation automatically performs the validation, and then displays error message 3183. For more information on the error and troubleshooting steps, see the error page for [MSSQLSERVER_3183](../../relational-databases/errors-events/mssqlserver-3183-database-engine-error.md).
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## SQL Server 2012 and earlier versions
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In [!INCLUDE [sssql11-md](../../includes/sssql11-md.md)] and earlier versions, this option doesn't exist. You need to use Trace Flag 3023 to enable the `CHECKSUM` option as a default for the `BACKUP` command. Trace Flag 3023 can be used dynamically by using a `DBCC TRACEON` statement, or it can be used as a startup parameter.
description: Find out how to use the net send command to broadcast a message in SQL Server. See how to determine which users are currently connected to SQL Server.
This topic describes how to broadcast a shutdown message in [!INCLUDE[ssnoversion](../../includes/ssnoversion-md.md)] by using the **net send** command. In the message, include the time the instance of [!INCLUDE[ssNoVersion](../../includes/ssnoversion-md.md)] will be stopped so that users can finish their tasks.
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## <aname="SSMSProcedure"></a>
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#### To broadcast a shutdown message
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1. From a command prompt, enter:
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**net send /users "message"**
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The **/users** option specifies that the message be sent to all users connected to the server
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# Broadcast a shutdown message from the command prompt
This article describes how to broadcast a shutdown message in [!INCLUDE [ssnoversion](../../includes/ssnoversion-md.md)] by using the `net send` command. In the message, include the time the instance of [!INCLUDE [ssNoVersion](../../includes/ssnoversion-md.md)] is going to stop, so that users can finish their tasks.
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<aid="SSMSProcedure"></a>
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## Broadcast a shutdown message
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1. From a command prompt, enter:
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```console
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net send /users "message"
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```
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The `/users` option specifies that the message is sent to all users connected to the server.
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> [!NOTE]
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> The **net send** command requires the messenger service to be running on both the sending and the receiving computers. The messenger service is disabled by default on Windows Server 2003. For information about **net send**, see the Windows documentation.
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On your network, it may be more appropriate to contact users by e-mail or the telephone. To determine which users are currently connected to [!INCLUDE[ssNoVersion](../../includes/ssnoversion-md.md)], use the Activity Monitor. For information on the Activity Monitor, see [Activity Monitor](../../relational-databases/performance-monitor/activity-monitor.md) and [Open Activity Monitor (SQL Server Management Studio)](../../relational-databases/performance-monitor/open-activity-monitor-sql-server-management-studio.md).
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## See Also
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[Start, Stop, Pause, Resume, Restart the Database Engine, SQL Server Agent, or SQL Server Browser Service](../../database-engine/configure-windows/start-stop-pause-resume-restart-sql-server-services.md)
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> The `net send` command requires the messenger service to be running on both the sending and the receiving computers. The messenger service is disabled by default on Windows Server 2003. For information about `net send`, see the Windows documentation.
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On your network, it might be more appropriate to contact users by e-mail or the telephone. To determine which users are currently connected to [!INCLUDE [ssNoVersion](../../includes/ssnoversion-md.md)], use the Activity Monitor. For information on the Activity Monitor, see [Activity Monitor](../../relational-databases/performance-monitor/activity-monitor.md) and [Open Activity Monitor in SQL Server Management Studio (SSMS)](../../relational-databases/performance-monitor/open-activity-monitor-sql-server-management-studio.md).
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## Related content
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-[Start, stop, pause, resume, and restart SQL Server services](start-stop-pause-resume-restart-sql-server-services.md)
Introduced in [!INCLUDE [ssSQL14](../../includes/sssql14-md.md)], the buffer pool extension provides the seamless integration of a nonvolatile random access memory (that is, solid-state drive) extension to the [!INCLUDE [ssDE](../../includes/ssde-md.md)] buffer pool to significantly improve I/O throughput. The buffer pool extension isn't available in every [!INCLUDE [ssNoVersion](../../includes/ssnoversion-md.md)] edition. For more information, see [Features Supported by the Editions of SQL Server 2016](~/sql-server/editions-and-supported-features-for-sql-server-2016.md).
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Introduced in [!INCLUDE [ssSQL14](../../includes/sssql14-md.md)], the buffer pool extension provides the seamless integration of a nonvolatile random access memory (that is, solid-state drive) extension to the [!INCLUDE [ssDE](../../includes/ssde-md.md)] buffer pool to significantly improve I/O throughput. The buffer pool extension isn't available in every [!INCLUDE [ssNoVersion](../../includes/ssnoversion-md.md)] edition. For more information, see [Editions and supported features of SQL Server 2022](../../sql-server/editions-and-components-of-sql-server-2022.md).
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## Benefits of the buffer pool extension
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## Capacity limitations
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SQL Server Enterprise edition allows a maximum buffer pool extension size of 32 times the value of `max server memory`.
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SQL Server Enterprise edition allows a maximum buffer pool extension size of 32 times the value of `max server memory (MB)`.
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SQL Server Standard edition allows a maximum buffer pool extension size of four times the value of `max server memory`.
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SQL Server Standard edition allows a maximum buffer pool extension size of four times the value of `max server memory (MB)`.
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## Best practices
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We recommend that you follow these best practices.
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- After you enable buffer pool extension for the first time, you should restart the SQL Server instance to get the maximum performance benefits.
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- Set the buffer pool extension so the ratio between the size of the physical memory (`max server memory`) and the size of the buffer pool extension of 1:16 or less. A lower ratio in the range of 1:4 to 1:8 might be optimal. For information about setting the `max server memory` option, see [Server memory configuration options](server-memory-server-configuration-options.md).
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- Set the buffer pool extension so the ratio between the size of the physical memory (`max server memory (MB)`) and the size of the buffer pool extension of 1:16 or less. A lower ratio in the range of 1:4 to 1:8 might be optimal. For information about setting the `max server memory (MB)` option, see [Server memory configuration options](server-memory-server-configuration-options.md).
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- Test the buffer pool extension thoroughly before implementing in a production environment. Once in production, avoid making configuration changes to the file or turning off the feature. These activities might have a negative effect on server performance because the buffer pool is significantly reduced in size when the feature is disabled. When disabled, the memory used to support the feature isn't reclaimed until the instance of SQL Server is restarted. However, if the feature is re-enabled, the memory is reused without restarting the instance.
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