About Logical Reads

Question

Problem:
1.
If you run a SQL code and you read the logical reads. is it benefit for performance issue to have low value of logical reads not matter what?
2.
What is the definition of logical reads?'
Im a beginner in performance tuning

Answer 1

Logical reads is a metric that can be used to evaluate query plans. Less logical reads is usually better. However, it's not the best metric, that's wallclock time, in my opinion. Particularly, looking blindly on logical reads, may lead you to think that
a plan with lots of CPU-expensive hashing operations are better than a simpler plan with nested loop joins.
The nice thing with logical reads over wallclock time, is that logical reads is not affected by other operations on the server.
OP, overall I agree with Erland, all other things being equal, less logical reads is better than more logical reads.
But sometimes other things are not all equal - it does you little good to trade logical reads for a ton of CPU instead!
However, logical reads *are* affected, dramatically, by other operations on the server - they are not as purely "logical" as one might like!  If your buffers are empty and you have to do physical IO to get the data, even the *logical* reads shows higher
numbers!  Exactly why this is the case is obscure, or complicated, or something, but it is.  Similarly even contention with other processes especially for buffer space can affect the "logical" reads to a small or larger extent.
But the good news is that sometimes logical reads are really, really cheap, so sometimes you can get a query that does 100,000 logical reads but runs in a tenth of second anyway.  Whether it's worth a battle to cut the logical reads down then, is up
to you.
HTH,
Josh