June 2009 - Posts

• SQL storms from your data grids

  As organizations start to deploy various data grids into their application layers, they may start to experience what I’d call a SQL storm —a massive number of simple SQL requests that are issued over a large number of concurrent database connections at Read More... Posted Monday, June 29, 2009 2:41 PM by Linchi Shea | 7 Comments Filed under: Performance, data grid, SQL storm, grid computing

• SAN vs. Disk Arrays: It goes a long way to be slightly more specific!

  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... Posted Friday, June 26, 2009 6:45 PM by Linchi Shea | 3 Comments Filed under: SAN, Storage

• Performance impact: Logical scan fragmentation -- 100% may not be as bad as 85%

  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... Posted Monday, June 22, 2009 1:02 PM by Linchi Shea | 5 Comments Filed under: Performance, Storage, Disk I/O, Logical scan fragmentation, Fragmentation Attachment(s): lsf.GIF

• I didn't know this!

  Everyone else probably knew, but I didn't know that you could do the following: SELECT 'abc' WHERE <some where clause conditions>; I probably didn't really miss anything, but was surprised that this worked! I mean, a SELECT statement that has a Read More... Posted Friday, June 19, 2009 3:10 PM by Linchi Shea | 12 Comments Filed under: Trivia

• Performance impact: SQL trace and user defined scalar functions

  Certain things just don’t go well together! No, not talking about liberals and Republicans. Rather, I’m talking about user defined scalar functions and SQL traces. If you run SQL Trace or SQL Profiler often, you’d find user defined scalar functions to Read More... Posted Monday, June 15, 2009 2:21 PM by Linchi Shea | 9 Comments Filed under: Performance, Profiler, UDF, SQL Trace Attachment(s): UDF_Trace.GIF

• T-SQL Exercise: Simplest data-loading script to produce worst query performance – June 7th Update

  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... Posted Sunday, June 07, 2009 10:31 PM by Linchi Shea | 1 Comments Filed under: Performance, Storage, SQL Server 2008, Query Processing, Disk I/O

• Distribution latency in transactional replication: Is a volume surge the culprit?

  If you use transactional replication, I have no doubt that from time to time you are asked to explain why there is an increased latency between the publisher and the subscriber. More often than not, this end-to-end latency is caused by latency in distributing Read More... Posted Friday, June 05, 2009 12:25 PM by Linchi Shea | 8 Comments Filed under: Performance, Replication Attachment(s): replStats.zip