SQL Server Execution Plans - Red Gate Software

Chapter 2: Graphical Execution Plans for Basic Queries
1. Select (Result) 9. Sort 17. Spool
2. Clustered Index Scan 10. Key Lookup 18. Eager Spool
3. NonClustered Index Scan 11. Compute Scalar 19. Stream Aggregate
4. Clustered Index Seek 12. Constant Scan 20. Distribute Streams
5. NonClustered Index Seek 13. Table Scan 21. Repartition Streams
6. Hash Match 14. RID Lookup 22. Gather Streams
7. Nested Loops 15. Filter 23. Bitmap
8. Merge Join 16. Lazy Spool 24. Split
Most operators behave in one of two ways, non-blocking or blocking. A non-blocking
operator creates output data at the same time as it receives the input. A blocking operator
has to get all the data prior to producing its output. A blocking operator might contribute
to concurrency problems, hurting performance.
An example of a non-blocking operator would be the Merge Join, which produces data
even as it is fed the data. We know this because the data in a Merge Join must be ordered
for it to work properly, so it can produce its output as the input comes in.
An example of a blocking operator would be the Hash Match join. It has to gather all the
data prior to performing its join operations and producing output. There are variations
on some operators that may behave in other ways, but these are internals known only to
Microsoft.
Again, the key to understanding execution plans is to start to learn how to understand
what the operators do and how this affects your query.
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