|
|
|
|
Checking out SQL Server via empirical data points
Browse by Tags
All Tags » Storage (RSS)
-
Okay, it’s a bit of a hyperbole. But let me elaborate. I regularly bump into SQL Server discussions, online or elsewhere, in which I hear people speaking with confidence that an operation is so and so because it is doing sequential disk I/Os or because Read More...
|
-
In the SQL Server communities, it's common to hear people talking about HP SAN, EMC SAN, 3Par SAN, and so on as if there were such things as HP SAN, EMC SAN, etc. Technically, SAN stands for Storage Area Network, but can be, and has been, used in two Read More...
|
-
In this previous post I asked whether 100% logical scan fragmentation is always worse than 85% local scan fragmentation for table/index scans. (To be precise, I was talking about a B-tree table, i.e. a table with a clustered index). The answer is no. Read More...
|
-
All the previously posted results ( May 25 th and May 29 th ) on this exercise were obtained with query parallelism disabled (i.e. the sp_configure ‘max degree of parallelism’ option was set to 1). Since the following test query is sensitive to query Read More...
|
-
This is another follow-up on the T-SQL exercise . So the test query below is rather simple: DBCC DROPCLEANBUFFERS go SELECT COUNT(*) FROM dbo.test; But beneath its simple appearance, many factors are at play and interact in a complex way to influence Read More...
|
-
This is a quick update on the T-SQL exercise I posted a few days ago. The goal was to write a simple T-SQL script to generate and load 4,000,000 rows into a table so that the following query would produce the worst performance, i.e. take longest time Read More...
|
-
Here is a T-SQL scripting exercise in case you have a few minutes to spare or are bored with whatever else you are doing. Objective The task is to write a simple T-SQL script to generate and load 4,000,000 rows into a test table. The objective is to make Read More...
|
-
A script to fragment a test file Well, this post won't cover any actual test results and is not specific to SAN. But in the spirit of full disclosure, I've attached the script I used to control the fragmentation level of the test files mentioned in this Read More...
|
-
SQL Server workloads So far, the discussions in all the previous posts ( 1 , 2 , 3 , and 4 ) on the performance impact of file fragmentation on a drive presented from a high-end enterprise-class disk array are related to disk I/O workloads. Ultimately, Read More...
|
-
Lies, damned lies, and statistics! If you have read my three previous posts ( 1 , 2 , 3 ), you may walk away with an impression that on a drive presented from a high-end enterprise class disk array, Windows file fragmentation does not have a significant Read More...
|
-
256KB Sequential Reads In my two previous posts ( 1 , 2 ), I highlighted the fact that while file fragmentation had a huge adverse performance impact on directly attached storage (DAS), it did not have much, if any, impact on the drive presented from Read More...
|
-
1KB Sequential Writes on DAS There were some questions about the use 1KB sequential writes in my previous post to test the performance impact of file fragmentation on a drive presented from a high end enterprise class disk array. There were two reasons Read More...
|
-
1KB Sequential Writes It’s well known that disk I/O performance can be severely impacted by fragmentation at the file system level. In other words, when a file is allocated space from many small fragments, its performance can be much worse than when its Read More...
|
-
There were discussions on disk misalignment on this site. See my previous post on “ Performance Impact of Disk Misalignment ”, and Kevin Kline’s blog on “ How to Improve Application and Database Performance up to 40% in One Easy Step ” But thanks to Jimmy Read More...
|
-
In the next series of posts, I'll focus on SQL Server I/O, revisiting some common issues and taking a closer look at some others. In each post and as always, I'll make the case with specific data points from my tests. For the first two posts in this series, Read More...
|
|
|
|
|
|