The document discusses common errors that can slow down SQL Server, including misunderstandings of parameter sniffing, the use of batches instead of stored procedures, and the misuse of temporary objects. It explains how these mistakes affect query plans and performance, highlighting differences between batch processing and stored procedures, as well as between table variables and temporary tables. Additionally, it warns against using excessively long column sizes which can lead to memory issues and inefficient query plans.

1. NAYA Technologies
COMMON ERRORS THAT SLOW
THE SERVER

2. TYPE OF ERRORS
1. Misunderstanding parameter sniffing
2. Using batches instead of procedures
3. Using wrong temporary objects
4. Using to long columns

3. WHAT IS PARAMETER SNIFING?
• When SQL Server creates a query plan for a
procedure, it uses the parameters’ values
to create the proper query plan

4. MISUNDERSTANDING PARAMETER SNIFING
• This behavior can lead to the fallowing
problems:
– Sometimes different values need different
plans
– The query plan is according to the values that
were passed and not according to the values
during runtime

5. Demo 1
• Parameter sniffing
– Working with procedures that different value
should use different plans.
– Avoiding modifying procedure’s parameters
during runtime.

6. Using batch instead of procedures

7. BATCH VS. PROCEDURE
• Batch might have a different and none optimal
query plan then a stored procedure.
• Batches might bloat the cache memory.

8. DEMO 2
• Demo 2
– Difference in query plan between batch and stored procedure
– Procedure cache and stored procedures and batches

9. USING WRONG TEMPORARY OBJECTS
• SQL Server has 2 types of objects that store
temporary data:
– Temporary tables
– Table variables
• The myth that table variable is better then
temporary table because it exists only in
memory and never written to the disk is
not true

10. TABLE VARIABLE VS. TEMPORARY TABLE
• Some of the differences between table
variable and temporary table are:
– Temporary tables have statistics. Table
variables don't. The server will always treat
the table variable as if it has exactly 1 row
– Inserting data into temporary tables cause
recompilation. Inserting data into table
variables doesn’t cause recompilation.

11. Demo 3
• Table variables, temporary tables and query
plans

12. Using to long columns
• SQL Server can use varying length columns
• For columns with varying length, the server
users the actual data length + 2 extra bytes

13. Using to long columns
• Many times DBA are using to big size
limitations on varying size columns
• Using to big maximum size for a column can
lead to memory problems and sometimes
to different query plans

14. Demo 4
• Influence of column’s maximum size on
memory consumption and query plans