Understanding Hybrid Buffer Pool in SQL Server

Manvendra Deo Singh — Sun, 30 Dec 2018 12:02:57 +0000

Microsoft introduces a new feature called Hybrid Buffer Pool in SQL Server 2019 CTP 2.1. This feature allows direct access of data pages in database files stored in persistent memory (PMEM) devices.

Before going ahead, you might be thinking what is Persistent Memory devices and how it is related to SQL Server. Let me first explain about persistent memory.

What is Persistent Memory?

Persistent memory generally termed as PMEM, is a solid-state high performance byte-addressable memory device that resides on the memory bus. It has many benefits over other storage devices.

The main advantages of persistent memory include:

It provides fast data access near real-time without any latency than flash SSDs for large data sets as well.
PMEM increases throughput more than flash storage.
Biggest benefit is its cost. It’s cheaper than DRAM.
PMEM is cacheable. This is a huge advantage over PCIe interconnect, which cannot be cached in the CPU.
It retains Data in memory after power interruption or shut off.

Persistent memory can be used in a variety of ways to deliver lower latency for applications where you need fast data access with enormous amount of data such as IoT applications, Cyber threat analysis, financial trading etc.

What is Hybrid Buffer Pool?

In a traditional system, SQL Server caches data pages in the buffer pool. With Hybrid Buffer Pool, SQL Server skips performing a copy of the page into the DRAM-based portion of the buffer pool, and instead references the page directly on the database file that lives on a PMEM device. Access to data files in PMEM for Hybrid Buffer Pool is performed using memory-mapped I/O, also known as enlightenment. This brings performance benefits from avoiding a copy of the page to DRAM, and from the avoidance of the I/O stack of the operating system to access the page on persistent storage.

Only clean pages can be referenced directly on a PMEM device. When a page becomes dirty it is kept in DRAM, and then eventually written back to the PMEM device.

This feature will be available in both Windows and Linux version of SQL Server 2019.

How to Enable Hybrid Buffer Pool?

We can enable Hybrid Buffer Pool for SQL Server instance by enabling trace flag during SQL Server startup. As of now, the current process is, we must enable the startup trace flag 809 in order to use Hybrid Buffer Pool.

Microsoft suggests a best practice to keep in mind while enabling
Hybrid Buffer Pool in SQL Server. We should use largest allocation size available for NTFS and ensure the device has been enabled for DAX (DirectAccess) while formatting the PMEM device on Windows.

I hope you liked this article. Please write your comments if you have any questions.

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10 New Features in SQL Server 2017 Database Engine

Manvendra Deo Singh — Thu, 05 Oct 2017 15:33:04 +0000

SQL Server 2017 is major release that are coming with lots of new features. The most debated new feature in SQL Server 2017 is its support for Linux based operating systems. Yes, now you can install and run SQL Server 2017 on Linux based operating system. Here i will discuss top 10 SQL Serve 2017 new features in this article.

SQL Server 2017 New Features in Database Engine

Let’s discuss SQL Server 2017 features. Below is the list of SQL Server 2017 new features introduced in database engine services.

SQL Server on Linux

SQL Server is not only Windows based RDBMS anymore now you can run it on different flavor of Linux operating systems. Now you can develop applications with SQL Server on Linux, Windows, Ubuntu, or Docker and deploy them as well on these platforms. SQL Server can now compete more directly with other RDBMS like Oracle which are more popular on Linux. We can say that SQL Server on Linux is one of the most popular SQL Server 2017 features. You can read below articles if you want to install SQL Server on Linux based operating systems.

Adaptive Query Processing

SQL Server 2017 introduce a new generation of query processing improvements that will adapt optimization strategies to your application workload’s runtime conditions. During optimization, the cardinality estimation process is responsible for estimating the number of rows processed at each step in an execution plan. When estimates are inaccurate, the query optimizer may make poor decisions regarding algorithm selection and order of operations. This is also one of the most awaited SQL 2017 new features.

Prior to SQL Server 2017, if we make poor assumptions due to bad cardinality estimates, we do not change our query plan execution strategy during execution. Read attached article Adaptive Query Processing to learn more about it.

Resumable Online Index Rebuild

Resumable Online Index Rebuild is another SQL 2017 feature. Now we can pause and resume online index rebuild operation. This feature will be very helpful. Resumable Online Index Rebuild allows you to resume an online index rebuild operation from where it stopped after a failure. For example, you might need to temporarily free up systems resources in order to execute a high priority task or complete the index rebuild in another maintenance window if the available maintenance windows is too short for a large table. Read attached articles to understand in depth information about this feature.

Automatic Database Tuning

Automatic tuning is a database feature that provides insight into potential query performance problems, recommend solutions, and automatically fix identified problems. Automatic tuning in SQL Server, notifies you whenever a potential performance issue is detected, and lets you apply corrective actions, or lets the Database Engine automatically fix performance problems.

Graph Database Capabilities

SQL Server offers graph database capabilities to model many-to-many relationships. The graph relationships are integrated into Transact-SQL and receive the benefits of using SQL Server as the foundational database management system.

A graph database is a collection of nodes (or vertices) and edges (or relationships). A node represents an entity (for example, a person or an organization) and an edge represents a relationship between the two nodes that it connects (for example, likes or friends). Both nodes and edges may have properties associated with them.

Cluster less Availability Groups

Now we can configure AOAG\Alwayson Availability group without windows cluster in SQL Server 2017. This feature is added because of another new feature that is to configure AOAG between windows and Linux based SQL Servers. Now you don’t need a windows cluster in place if you want to configure AOAG between windows and Linux based SQL Servers.

Cross-OS AOAG

Availability Groups can now work across Windows-Linux to enable cross-OS migrations and testing. Now we can configure AOAG between windows based SQL Server and Linux based SQL Server. That is why, Microsoft has also given an option for clusterless AOAG.

New Functions

There are few new T-SQL functions added to SQL Server 2017. Below is the list of those new functions. You can click on hyperlinks to get more about them. These functions are very useful for SQL developers.

New DMVs

There are many new DMVs have been introduced as SQL 2017 new features. Below is the list of such DMVs that have been introduced in SQL Server 2017. You can click on hyperlinks to get more about them.

sys.dm_tran_version_store_space_usage – Introduced to track version store usage per database.
sys.dm_db_stats_histogram (Transact-SQL) is added for examining statistics.
sys.dm_exec_query_statistics_xml
sys.dm_os_host_info is added to provide operating system information for both Windows and Linux.
sys.dm_os_sys_info has three new columns added: socket_count, cores_per_socket, numa_node_count.
A new column modified_extent_page_count, is introduced in sys.dm_db_file_space_usage to track differential changes in each database file of the database.

New DMFs

Below is the list of new DMFs introduced in SQL Server 2017. You can click on hyperlinks to get more about them.

This DMF sys.dm_db_log_info is introduced to expose the VLF information similar to DBCC LOGINFO to monitor, alert, and avert potential transaction log issues caused due to number of VLFs, VLF size or shrinkfile issues experienced by customers.
Another DMF sys.dm_db_log_stats, is introduced to expose summary level attributes and information on transaction log files. This is very useful for monitoring the health of the transaction log.

Here, i have explained about SQL Server 2017 new features. I hope you like this article. Please follow us on our facebook page and on Twitter handle to get latest updates.