Time to count records the first time


I'm doing a stress test on an application that I'm developing. I added a few million records to a table, which is what it will take in about 5 years of use. I use Entity Framework. When counting records of a query , it took a long time to occur. I thought it was EF's problem. But when I do a trace in SQL Server and run the query directly in the database I noticed that the delay is in SQL Server itself.

Look at the following query example, similar to that generated by EF, but much simpler and still takes a long time:

select count(1) from tbMovimentoConta where con_codigo_fk = 1 and mcon_data >= '2017-01-01' and mcon_data <= '2018-01-01'

Result: 1,162,158 records

Time: 24 seconds

Repeating the query is instantaneous, I believe because of the cache. However, if you clear the cache with the DBCC DROPCLEANBUFFERS command it will take about 25 seconds again.

The con_codigo_fk field used in the where of the above query is a foreign key and has index.

The mcon_data field also used in where of the above query has index too.

This table has four more foreign key indexes, plus two indexes for the mcon_dataExclusao and mcon_dataInclusao fields that are used in searches.

Script of the index of the column mcon_data to analyze and point out some possible failure in it.

CREATE NONCLUSTERED INDEX [ix_mcon_data] ON [dbo].[tbMovimentoConta]
    [mcon_data] ASC

Is this delay for this amount of records normal? Does not seem that big to me. I do not know if it's the amount of indexes, or the way they were created. I'm investigating.

Computer Configuration: 8GB of RAM and Core I7

asked by anonymous 05.01.2017 / 11:50

2 answers


Without proper registration it is normal. and needs to be done fast then create an index for this. It will probably resolve if you use con_codigo_fk and mcon_data in the key.

CREATE INDEX [ix__con_codigo_fk__mcon_data]
    ON [dbo].[tbMovimentoConta] ([con_codigo_fk], [mcon_data]);

Read also:

05.01.2017 / 12:15

As @bigown said, something was wrong with the current indexes. Searching, and resorting to help on another web site , I got the solution.

The solution was to create a compound index for the columns mcon_data and con_codigo_fk

CREATE INDEX ix__con_codigo_fk__mcon_data
ON dbo.tbMovimentoConta
(con_codigo_fk, mcon_data) ;

After the creation of this index, the query is so fast that it does not take a second (my Management Studio does not show the milliseconds).

06.01.2017 / 11:21