November 17, 2008 at 7:18 pm
In execution plan what are the bad things,,and what are the good
things to consider???How do you optimize a querey perfomance using
execution plan???
November 18, 2008 at 12:47 am
Generally you need to identify those parts of the query that are costing you the most resources. Looking at the estimated cost on the tiop node, and workinmg down branches will help show you where the "expensive" parts are. Also looking for simople tghings like big thick lines - indicates that large numbers of rows are being processed. Tablse scans are generally a "bad thing" as are index scans. Index seeks are normally a "good thing". The reason for saying generally is that if you have a query with no where clause it will by definition do a table scan or index scan, sao saying they are ALWAYS a bad thing is not always correct.
Having identified the costly bits, you can help things by adding indexes/removing indexes, sometimes rewriting a badly written query and so on.
That is only a small starter on this sort of thing, a thorough understanding of indexing, join techniques and SQl in general is really needed to properly understand what the plan is telling you. "Inside SQL Server" covers lots of this sort of thing.
Mike
November 18, 2008 at 2:42 am
usually a graphical execution plan is read from right to left and top to bottom. Scans are bad and seeks are good. there are two types of execution plans
Estimated (generated by optimizer)
And actual (generated by query execution)
Execution plans may be saved in plan cache and may be re used.
DBDigger Microsoft Data Platform Consultancy.
November 18, 2008 at 2:46 am
In the graphical execution plan you can find many options, for example, based data getting arrow marks shows thin line to thick lines. For more information see SQL BOL.
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