BY Jim Bennett
Do you have databases that are mirrored that your ETL is populating? Does the database mirror ever start to lag?
If you answered yes to either of these questions then this is for you. SQL Server has a handy table that is created when database mirroring is configured. This table (msdb.dbo.dbm_monitor_data) allows you to see the status of your mirrored databases. So how can we make use of this in ETL? By using the code provided below, you can pause your ETL if database mirroring is behind and give SQL Server a chance to catch up before you start loading more data from your ETL process.
The usp_CheckMirroringStatus stored procedure does two things for you: 1) it captures information about the status of the mirrored database and logs this information to a table (dbo.MirroringStatus). This can help show you longer term trends about how mirroring is working on the server. 2) the stored procedure will not finish until the redo_queue falls below your threshold. This essentially can give the SQL Server some breathing room before more data is introduced from your ETL.
Overall this is a handy piece of logic that can be baked-in to your ETL process for those times when your server is not keeping up with your ETL process.
IF EXISTS (SELECT 1 FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[MirroringStatus]') AND type in (N'U'))
DROP TABLE [dbo].[MirroringStatus]
GO
PRINT 'Create Table dbo.MirroringStatus'
GO
CREATE TABLE [dbo].[MirroringStatus](
[Id] [int] IDENTITY(1,1) NOT NULL,
database_name varchar(128),
mirroring_state varchar(20),
witness_status varchar(15),
log_flush_rateKBs int,
send_queue_sizeKB int,
send_rateKBs int,
redo_queue_sizeKB int,
redo_rateKBs int,
transaction_delayMS int,
transactions_per_sec int,
local_time datetime,
end_of_log_lsn numeric(25,0),
failover_lsn numeric(25,0)
CONSTRAINT [PK_MirroringStatus] PRIMARY KEY CLUSTERED
(
[Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON)
)
GO
IF EXISTS (SELECT 1 FROM sys.procedures WHERE name = 'usp_CheckMirroringStatus')
DROP PROCEDURE [dbo].[usp_CheckMirroringStatus]
GO
PRINT 'Create SP dbo.usp_CheckMirroringStatus'
GO
CREATE PROCEDURE [dbo].[usp_CheckMirroringStatus]
@dbname varchar(128),
@RedoQueueThresholdKB int = 1024,
@WaitDelayTimeInSeconds int = 15
AS
/*
Procedure Name: usp_CheckMirroringStatus
Created By: Jim Bennett – CapstoneBI
Created Date: 10/20/2010
Website: www.capstonebi.com
Purpose: Allows database mirroring to be monitored and cause calling
process to wait until mirroring is caught up.
*/
DECLARE @isFinished tinyint = 0;
DECLARE @CurrentRedoQueueSizeKB int;
CREATE TABLE #Result
(
database_id int,
role int,
mirroring_state int,
witness_status int,
log_flush_rate int,
send_queue_size int,
send_rate int,
redo_queue_size int,
redo_rate int,
transaction_delay int,
transactions_per_sec int,
[time] datetime,
end_of_log_lsn numeric(25,0),
failover_lsn numeric(25,0),
local_time datetime
)
IF (
SELECT COUNT(*)
FROM sys.database_mirroring
WHERE database_id = DB_ID(@dbname)
AND mirroring_guid IS NOT NULL
) > 0
BEGIN
--The database is being mirrored
PRINT 'Database: ' + @dbname + ' is mirrored'
WHILE (@isFinished = 0)
BEGIN
TRUNCATE TABLE #Result;
PRINT 'Checking Redo Queue Size'
INSERT INTO #Result
SELECT TOP 1 *
FROM msdb.dbo.dbm_monitor_data WITH (NOLOCK)
WHERE database_id = DB_ID(@dbname)
ORDER BY [time] DESC
SELECT
@isFinished = CASE WHEN redo_queue_size <= @RedoQueueThresholdKB THEN 1 ELSE 0 END,
@CurrentRedoQueueSizeKB = redo_queue_size
FROM #Result
PRINT 'Current RedoQueue Size in KB: ' + CAST (@CurrentRedoQueueSizeKB as varchar(50))
IF (@isFinished = 0)
WAITFOR DELAY @WaitDelayTimeInSeconds
INSERT INTO dbo.MirroringStatus
(
[database_name],
mirroring_state,
witness_status,
log_flush_rateKBs,
send_queue_sizeKB,
send_rateKBs,
redo_queue_sizeKB,
redo_rateKBs,
transaction_delayMS,
transactions_per_sec,
local_time,
end_of_log_lsn,
failover_lsn
)
SELECT
db_name(database_id),
CASE mirroring_state
WHEN 0 THEN 'Suspended'
WHEN 1 THEN 'Disconnected'
WHEN 2 THEN 'Synchronizing'
WHEN 3 THEN 'Pending Failover'
WHEN 4 THEN 'Synchronized'
ELSE 'Unknown'
END,
CASE witness_status
WHEN 0 THEN 'Unknown'
WHEN 1 THEN 'Connected'
WHEN 2 THEN 'Disconnected'
ELSE 'Unknown'
END,
log_flush_rate,
send_queue_size,
send_rate,
redo_queue_size,
redo_rate,
transaction_delay,
transactions_per_sec,
local_time,
end_of_log_lsn,
failover_lsn
FROM #Result
END
DROP TABLE #Result
END
ELSE
PRINT 'Database: ' + @dbname + ' is not mirrored'
GO
.
