The ASYNC_NETWORK_IO wait type is one of those wait types that can be seen very often by DBAs, and it can be worrisome when excessive values occur, as it is one of the most difficult wait types to fix.

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

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 the parallel plan.

The SQL Server SOS_SCHEDULER_YIELD is a fairly common wait type and it could indicate one of two things:

Background

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.

CXPACKET is one of the famous wait types that database administrators are experiencing. Before moving into the details of the CXPACKET wait type, first, let us discuss 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 the 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 wait, there are more than 200 wait types. CXPACKET, WRITELOG, ASYNC_NETWORK_IO are the most common wait types. This is a 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 intended to discuss waits in detail.