SQL SERVER – LOGBUFFER – Wait Type – Day 18 of 28

At first, I was not planning to write about this wait type. The reason was simple- I have faced this only once in my lifetime so far maybe because it is one of the top 5 wait types. I am not sure if it is a common wait type or not, but in the samples I had it really looks rare to me.

From Book On-Line:

Occurs when a task is waiting for space in the log buffer to store a log record. Consistently high values may indicate that the log devices cannot keep up with the amount of log being generated by the server.

LOGBUFFER Explanation:

The book online definition of the LOGBUFFER seems to be very accurate. On the system where I faced this wait type, the log file (LDF) was put on the local disk, and the data files (MDF, NDF) were put on SanDrives. My client then was not familiar about how the file distribution was supposed to be. Once we moved the LDF to a faster drive, this wait type disappeared.

Reducing LOGBUFFER wait:

There are several suggestions to reduce this wait stats:

  • Move Transaction Log to Separate Disk from mdf and other files. (Make sure your drive where your LDF is has no IO bottleneck issues).
  • Avoid cursor-like coding methodology and frequent commit statements.
  • Find the most-active file based on IO stall time, as shown in the script written over here.
  • You can also use fn_virtualfilestats to find IO-related issues using the script mentioned over here.
  • Check the IO-related counters (PhysicalDisk:Avg.Disk Queue Length, PhysicalDisk:Disk Read Bytes/sec and PhysicalDisk :Disk Write Bytes/sec) for additional details. Read about them over here.

If you have noticed, my suggestions for reducing the LOGBUFFER is very similar to WRITELOG. Although the procedures on reducing them are alike, I am not suggesting that LOGBUFFER and WRITELOG are same wait types. From the definition of the two, you will find their difference. However, they are both related to LOG and both of them can severely degrade the performance.

Note: The information presented here is from my experience and there is no way that I claim it to be accurate. I suggest reading Book OnLine for further clarification. All the discussion of Wait Stats in this blog is generic and varies from system to system. It is recommended that you test this on a development server before implementing it to a production server.

Reference: Pinal Dave (https://blog.sqlauthority.com)


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2 Comments. Leave new

  • I have seen this wait type recently at the times VMWare had experienced a LUN reset which upsets the connectivity.The SPIDs that were performing an Update at the time became suspended with a Log Buffer wait.

  • We have similar issue going on where delete command is running from 2 days. Due to this log file is growing too much around 200 gb.


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