Question

I need your help 🙂

I have a table in a database (SQL Server 2008 R2). Currently there are around 4M rows.

Consumer apps take rows from there (lock them and process).

To protect rows from being taken by more than one consumer I’m locking it by adding some flag into appropriate column…

So, to “lock” record I do

SELECT TOP 1  .....

and then UPDATE operation on record with some specific ID.

This operation takes up to 5 seconds now (I tried in SQL Server Management Studio):

SELECT TOP 1 * 
FROM testdb.dbo.myTable 
WHERE recordLockedBy is NULL;

How can I speed it up?

Here is the table structure:

CREATE TABLE [dbo].[myTable](
[id] [int] IDENTITY(1,1) NOT NULL,
[num] [varchar](15) NOT NULL,
[date] [datetime] NULL,
[field1] [varchar](150) NULL,
[field2] [varchar](150) NULL,
[field3] [varchar](150) NULL,
[field4] [varchar](150) NULL,
[date2] [datetime] NULL,
[recordLockedBy] [varchar](100) NULL,
[timeLocked] [datetime] NULL,
[field5] [varchar](100) NULL);

Answer 1

Indexes should be placed on any columns you use in your query’s where clause. Therefore you should add an index to recordLockedBy.

If you don’t know about indexes look here