Quote: "Database stuff, all this programming stuff, is easy. Anyone can do it. That's why everyone in the company has sa privileges." For nine months, I worked in an environment where everyone, from developers to QA to the sales people to the receptionist, had SA privileges. You know what? DBA skills are necessary. I speak from the point of view of someone that has had to recover a server after a salse person helpfully "cleaned up the temporary stuff on the server" by dropping tempdb, causing a late deployment for a client. I speak from the point of view of the guy who kept a window open on his desk with the database restore script ready to run, all day long, because of "accidents" that stopped development until I could get the…
I try to watch the search phrases that point people to the blog because sometimes, you get a sense of what problems people are running into. The latest question or phrase I've seen a lot lately is along the lines of "how do you know if an execution plan is being reused." Since compiling an execution plan can be an extremely expensive operation, it's worth your time to understand how well a given plan is getting reused. If you've seen me present, I'll frequently talk about the application that had a query with an 86 table join. Recompiles on that thing were frequent and extremely costly. The only good news was, they were recompiles. If we weren't getting plan reuse it would have been an even worse system than it was. There are…
I am not a Reporting Services guru and nor do I play one on TV. I am however forced to be all things Microsoft Data where I work. So I frequently find myself stretching way beyond my abilities. I just had to get a report running that feeds from a web service and has a recursive hiearchy with customized aggregation on multiple fields with drill down to a different set of details. Yeah, through the internet I can see the SSRS monsters rolling their eyes at the ease of this task. But for us mere mortals it was work. Since I spent so much time learning how to do it, I thought I'd share. XML as a Source First, because we have a very paranoid (and appropriately so) group of…
Nice to see most of you have managed to fight your way through the shoggoths outside to attend another lecture at the Miskatonic branch of SQL University. This will be the third and final part of the introduction to indexes lecture. Please, if you're going mad, step out into the hall. Our previous two lectures introduced the concept of indexes and then talked about two types of indexes, clustered and nonclustered. This lecture will cover the concept of statistics as they relate to indexes. If you followed the previous lecture then you know that indexes are stored in a Balanced Tree or B-Tree structure. You know that this storage mechanism is intended to provide fast retrieval of data. But, how can the query engine inside SQL Server know which index…
Welcome once more to the Miskatonic branch of SQL University. Please try to concentrate. I realize the whipoorwills singing outside the window in a coordinated fashion that sounds almost like laboured breathing can be distracting, but we're talking about indexes here. We left last class with a general idea what an index is, now it's time for some specifics. There are several different kinds of indexes, as we talked about last class. But the two you're probably going to work with the most are clustered, non-clustered. Each of these indexes is stored in a structure called a B-Tree, a balanced tree, not a binary tree. That's a very important distinction. A B-Tree is a double-linked list that is defined by the keys of the indexes on the top and intermediate pages, and…
I'm continuing to evaluate Confio's Ignite database monitoring tool. I've had it collecting data on a couple of production servers for about a week now. Based on what I've seen so far, it's looking like a pretty good piece of software. Breaking with the usual tradition, I'm going to talk about the things I'm not crazy about with the software, before I start singing its praises. The first thing, that I thought was missing, but is actually just hard to find, is the ability to look at the query information that Ignite collects, broken down by database. It looks like you should be able to get to it by looking at the Databases tab, but instead you have to first drill down into a time-period, then select specific databases within that time period,…
Not everyone has the opportunity to call Microsoft Premier Support. For those who have not yet had this experience, I'll document my most recent, non-critical, call. Critical calls are a different critter entirely. We were experiencing a very odd error on one server in our system. When a particular procedure was run with a particularly large set of data, it would produce an error, but only when called from the application. The exact same error with exactly the same data called from SSMS did not produce an error. We went through a very extensive set of tests and were unable to fix the problem on the server. After moving the production system that was experiencing the issue to a different server, we decided to contact PSS. 8:48 Am, Tuesday: I made the…
No, I'm not talking about a Dickens novel. I'm talking about the number of characters in a string. I had a painful time recently because of the word "characters."Â If you take a look at the dynamic management view sys.dm_exec_sql_text you can get the queries that have been run on your system that are still in the cache. It's a great utility. Better still, you can get specific statements from the code that are actively running through sys.dm_exec_requests or ones that have run through sys.dm_exec_query_stats. To do this is very simple. Each of these DMV's has a pair of columns, statement_start_offset and statement_end_offset. These columns, and I'm quoting directly from books online measure the "number of character" offset from the beginning of the SQL string and from the end of…
I keep seeing these concepts that have long been disproven, posted again and again on newsgroups as if they were valid information. The latest? Table variables are better because they're only in memory where as temporary tables write to the disk through tempdb. This one is abjectly wrong. I'm not even going to hedge with "it depends." From a macro point of view, there are only a few differences between temporary tables and table variables, statistics being the biggest. Temporary tables have 'em and table variables don't. Other than that, both will reside completely in memory or will swap out to the disk through tempdb, depending on their size. Some of the minor differences, and why you might want to use table variables over temporary tables, table variables won't cause a statement recompile while temporary tables will, table…
Another frequently heard story is that stored procedures get and reuse execution plans, but ad hoc queries do not. A lot of people believe this and say as much online and in the real world. Unlike my last myth, this time, I'm going to give you the DBA answer to this question. It depends. There are ad hoc queries and there are ad hoc queries. The classic ad hoc query looks like this: DECLARE @sql NVARCHAR(MAX), @value int; SET @value = 43668; SET @sql = 'SELECT * FROM Sales.SalesOrderHeader AS soh '; SET @sql = @sql + 'JOIN Sales.SalesOrderDetail AS sod '; SET @sql = @sql + 'ON soh.SalesOrderID = sod.SalesOrderID '; SET @sql = @sql + 'WHERE soh.SalesOrderID = ' + CAST(@value AS NVARCHAR); EXEC (@sql); And as ad…