May 6, 2008 at 9:27 am
Hi,
I just started to use Execution Plan.
But I have difficulty to understand it.
In my Execution Plan I have:
Table Scan, Clustered Index Scan, Key Lookup,
Hash Match, Filter, Nested Loops,etc.
What are the bad signs?
For example, Clustered Index Scan
is 83%. Is it good or bad?
May 6, 2008 at 10:11 am
You'd have to read about performance tuning. Seeks are good, scans aren't. There are various performance tuning books out there, Ben-Gans is the best I think that can help you understand them.
We will be marketing a new book here soon by Grant Fritchey that looks great. Look for that in 2-4 weeks.
May 6, 2008 at 12:29 pm
I should be too embarassed to reply, but what the heck...
Scans are usually bad, but not always. Depending on the scan itself, it means it's reading all, or a substantial portion, of the table. Look at the tool tip that pops up. That'll tell you the predicates that are being searched against the clustered index. Probably they're not part of the index itself, but rather the data is being scanned out of the table. What to do about it? That depends on a lot of stuff, but the short answer is put an index on the predicates that aren't being covered by some other index.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning
May 6, 2008 at 1:12 pm
I love SQLServerCentral!
You can talk live to some big guys here! .. )
Thank you for advice Grant.
Rob
May 6, 2008 at 1:25 pm
I'll have you know I'm down to 203 and at 6'1" that's not big, just a tad plump. It's sitting on my brain all day long that causes the problems. 😉
Regardless. Everyone on here learns from everyone else. I do more than most.
Itzik Ben-Gan's book on TSQL Querying is invaluable. Pick that up. Kalen Delaney's book on performance tuning is supposed to be good. I haven't read it yet, but it's on my list. These will help you get started.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning
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