I have the following configuration:
Basically what I want to do is a select with a where clause on a table. The problem is the table has about 700M entries and the query takes a really long time.
Can you please indicate some pointers on where to optimize the query or what sort of techniques are can I use in order to get an improvement in performance?
Thanks.
Using indexes is the standard technique used to deal with this problem. As requested, here are some pointers that should get you started:
The first thing I do in this case is isolate whether it is the amount of data I am returning that is the problem or not (an i/o issue). A simple non-scientific way to do this is change your query to just return the count:
select count(*) --just return a count, no data!
from MyTable
inner join MyOtherTable on ...
where ...
If this runs very quickly, it tells you your indexes are in order (assuming no sub-selects in your WHERE
clause). If not, then you need to work on indexes , the WHERE
clause, or your query construction itself (JOINs being done, etc).
Once that is satisfactory, add back in your SELECT
clause. If it is slow, you are going to have to look at your data access pattern:
I would run Profiler to find the exact query that is being generated. ORMs can create less than optimal queries. Once you know the query, you can run it in SSMS and see the execution plan. This will give you clues as to where you have performance problems.
Several things that can cause performance problems:
There's more (After all whole very long books are written o nthis subject) but that should be enough to get you started at where to look.
You should provide some indexes for those column you often use to restrict the result. Other thing is the pagination of the result set.
Regardless of the specific DB, I would do the following:
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