Wait types

Ahmad Yaseen

SQL Server read-ahead mechanism; concept and performance gains

December 21, 2017 by

The user’s read requests in SQL Server are managed and controlled by the SQL Server Relational Engine, that is responsible for determining the most optimized access method, such as index scan or table scan, to retrieve the requested data. These read requests are also optimized internally by the SQL Server Storage Engine, the buffer manager components specifically, that is responsible for determining the general read pattern to be performed.

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Nikola Dimitrijevic

Handling excessive SQL Server PAGEIOLATCH_SH wait types

July 5, 2016 by

One of the most common wait type seen on SQL Server and definitely one that causes a lot of troubles to less experienced database administrators is the PAGEIOLATCH_SH wait type. This is one of those wait types that clearly indicates one thing, but which background and potential causes are much subtler and may lead to erroneous conclusions and worse, incorrect solutions

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Nikola Dimitrijevic

Troubleshooting the CXPACKET wait type in SQL Server

June 8, 2016 by

The SQL Server CXPACKET wait type is one of the most misinterpreted wait stats. The CXPACKET term came from Class Exchange Packet, and in its essence, this can be described as data rows exchanged among two parallel threads that are the part of a single process. One thread is the “producer thread” and another thread is the “consumer thread”. This wait type is directly related to parallelism and it occurs in SQL Server whenever SQL Server executes a query using parallel plan.

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Timothy Smith

Troubleshooting some waits issues

May 10, 2016 by


On occasion, I’ll see waits that exceed what I expect well above normal and a few of them have some architecture and standards to consider following when troubleshooting, though like most waits’ issues, there can be other underlying factors that are happening as well. In this article, I investigate the three waits ASYNC_NETWORK_IO and WRITELOG. In general, waits vary by environment and server, so before reading this article an immediate question to ask is, “Do you know what’s normal for yours?” When a wait suddenly spikes, or if the architecture is designed in a manner that should prevent a specific wait from consuming time, and yet you see that the wait does, I would be concerned. In addition, because applications and environments differ by architecture, you may want to consider other troubleshooting steps, as these may not apply to your situations.

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Dinesh Asanka

How to Avoid CXPACKETs?

November 25, 2015 by

CXPACKET is one of the famous wait type that database administrators are experiencing. Before moving into the details of CXPACKET wait type, first let us discuss about the waits in SQL Server in brief.

SQL Server is a mini operating system. When SQL Server is executing any task and if for any reason it has to wait for resources to execute the task, it will wait in a list until it gets the relevant resources. This list is called Waiter list or suspended list. This is not a queue as whenever that task is ready with required resources it will move to the runnable queue which means that it is ready to execute whenever the processor is free to execute. Depending on the type of the wait, there are more than 200 wait types. CXPACKET, WRITELOG, ASYNC_NETWORK_IO are the most common wait types. This is very brief discussion about waits. For any case where this is not clear, it will be better to get more details from other sources as this article is not intend to discuss about waits in detail.

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