Inconsistent cursor results when looping over databases

Question

I have several databases named very similar (my-db-1, my-db-2, my-db-3, my-db-4). I want to execute the same stored procedure on each of these databases. I decided to use cursors. However, I am getting some strange issues. First here is my simple code that I am executing through SQL Server Management Studio 2008.

DECLARE @db_cursor CURSOR 
DECLARE @name varchar(255)
DECLARE @Sql nvarchar(4000)

SET @db_cursor = CURSOR FOR  
SELECT name FROM sys.databases WHERE name LIKE 'my-db-%'

OPEN @db_cursor   
FETCH NEXT FROM @db_cursor INTO @name   

WHILE @@FETCH_STATUS = 0   
BEGIN  

    SET @Sql = 'Use [' + @name + ']; PRINT DB_NAME();'
    exec sp_sqlexec @Sql

    FETCH NEXT FROM @db_cursor INTO @name   
END   

CLOSE @db_cursor   
DEALLOCATE @db_cursor

Executing this multiple times in a row within 2 seconds, I get strange results:

Execution1:

my-db-1
my-db-2
my-db-3
my-db-4

Execution2:

my-db-1
my-db-2

Execution3:

my-db-1
my-db-2
my-db-3
my-db-4

Execution4:

my-db-1

It seems like its completely random. Sometimes I'll get all 4 databases to print after 10 executions. Sometimes after just 2 executions only 1 database will get printed.

This SQL is executing on Microsoft SQL Server 2008 R2 (RTM) - 10.50.1600.1 (X64) Apr 2 2010 15:48:46 Copyright (c) Microsoft Corporation Developer Edition (64-bit) on Windows NT 6.1 (Build 7600: ) through Microsoft SQL Server Management Studio 10.50.1600.1

Does anyone have any ideas?

Answer 1

Try declaring your cursor as FAST_FORWARD.

The default is an updateable cursor and these required update locks probably conflict with another process accessing sys.databases

Ref.: DECLARE CURSOR