Troubleshooting Transactional Replication Latency

Oct 19, 2007

Hello!

We have setup up transactional replication with dedicated distributor in SQL Server 2005 environment. I have noticed that during particular time of the day latency is increasing dramatically. I have been checking Tracer Tokens and Total latency during that time is around 30-40 min (both publisher to distributor and distributor to subscriber is taking much longer that normal). Normally, it is less than 10 sec. I was wondering if there is a way to pinpoint exact cause of the latency. This is pull subscription.
I would appreciate if someone can share (or point to the right direction) best practice on transactional replication setup/maintenance. My understanding is that only committed transactions are replicated, correct? I checked database on publisher and didn't see any outstanding long running transaction.

Any help is greatly appreciated.

Thanks,
Igor

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Monitor Transactional Replication Latency

Jun 12, 2008

CREATE PROCEDURE [dbo].[proc_replication_latency_monitor]
AS

-- Procedure created by Henning Frettem (Lumbago), www.sqlteam.com, 12th of June 2008

BEGIN

SET NOCOUNT ON

DECLARE
@PublishedDBName varchar(200),
@SQL nvarchar(2000),
@PublicationPK int,
@PublicationName varchar(200),
@PublicationDatabase varchar(200),
@TracerTokenID int,
@Parmameters nvarchar(500)

DECLARE @Publications table (
PublicationPK int IDENTITY(1, 1) PRIMARY KEY CLUSTERED,
PublicationDatabase varchar(200),
PublicationName varchar(200),
TracerTokenID int,
TracerTokenPostTime datetime
)

DECLARE @Latency table (
PublicationPK int,
DistributorLatency bigint,
Subscriber sysname,
SubscriberDB sysname,
SubscriberLatency bigint,
OverallLatency bigint
)

--> Cursor for fetching all publications in all databases
DECLARE curPublishedDatabases CURSOR LOCAL FAST_FORWARD FOR
SELECT [name] FROM sys.databases WHERE is_published > 0

OPEN curPublishedDatabases
FETCH curPublishedDatabases INTO @PublishedDBName
WHILE @@FETCH_STATUS = 0
BEGIN
SET @SQL = N'SELECT ''' + @PublishedDBName + ''', [name] FROM ' + @PublishedDBName + '.dbo.syspublications'
INSERT INTO @Publications (PublicationDatabase, PublicationName)
EXEC sp_executesql @SQL

FETCH NEXT FROM curPublishedDatabases INTO @PublishedDBName
END

CLOSE curPublishedDatabases
DEALLOCATE curPublishedDatabases

--> Cursor for posting tracer tokens
DECLARE curPublications CURSOR LOCAL FAST_FORWARD FOR
SELECT PublicationPK, PublicationDatabase, PublicationName FROM @Publications

OPEN curPublications
FETCH curPublications INTO @PublicationPK, @PublicationDatabase, @PublicationName
WHILE @@FETCH_STATUS = 0
BEGIN
SET @Parmameters = N'@PublicationName varchar(200), @TracerTokenID_OUT int OUTPUT';
SET @SQL = N'EXEC ' + @PublicationDatabase + '.sys.sp_posttracertoken @publication = @PublicationName, @tracer_token_id = @TracerTokenID_OUT OUTPUT'
EXEC sp_executesql @SQL, @Parmameters, @PublicationName = @PublicationName, @TracerTokenID_OUT = @TracerTokenID OUTPUT

UPDATE @Publications SET
TracerTokenID = @TracerTokenID,
TracerTokenPostTime = GETDATE()
WHERE PublicationPK = @PublicationPK

FETCH NEXT FROM curPublications INTO @PublicationPK, @PublicationDatabase, @PublicationName
END
CLOSE curPublications
DEALLOCATE curPublications

--> Wait two minutes for all tokens to be commited at all subscribers
WAITFOR DELAY '000:02:00.000'

--> Then check the results for each posted token
DECLARE curTokens CURSOR LOCAL FAST_FORWARD FOR
SELECT PublicationPK, PublicationDatabase, PublicationName, TracerTokenID FROM @Publications

OPEN curTokens
FETCH curTokens INTO @PublicationPK, @PublicationDatabase, @PublicationName, @TracerTokenID
WHILE @@FETCH_STATUS = 0
BEGIN
--> Insert token history for each token
SET @SQL = N'EXEC ' + @PublicationDatabase + '.dbo.sp_helptracertokenhistory @publication = ''' + @PublicationName + ''', @tracer_id = ' + CAST(@TracerTokenID AS VARCHAR(50)) + ''
INSERT INTO @Latency
(DistributorLatency, Subscriber, SubscriberDB, SubscriberLatency, OverallLatency)
EXEC sp_executesql @SQL

--> Make sure that the PublicationPK is added to the token history
UPDATE @Latency SET PublicationPK = @PublicationPK WHERE PublicationPK IS NULL

--> Clean up the tracer token
SET @SQL = N'EXEC ' + @PublicationDatabase + '.sys.sp_deletetracertokenhistory @publication = ''' + @PublicationName + ''', @tracer_id = ' + CAST(@TracerTokenID AS VARCHAR(50)) + ''
EXEC sp_executesql @SQL

FETCH NEXT FROM curTokens INTO @PublicationPK, @PublicationDatabase, @PublicationName, @TracerTokenID
END
CLOSE curTokens
DEALLOCATE curTokens

SELECT
b.PublicationDatabase,
b.PublicationName,
a.Subscriber,
a.SubscriberDB,
a.OverallLatency,
b.TracerTokenPostTime
FROM @Latency a
INNER JOIN @Publications b
ON a.PublicationPK = b.PublicationPK

END

--
Lumbago

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Typical Latency In Transactional Replication

Jul 31, 2007

I have been working on a project to evaluate transactional replication in SQL Server 2005 to find out if it will be suitable to provide real time reporting without impacting the primary database server. Thus far I have not seen latency better than several seconds replicating a change to a table or by utilizing the "tracer tokens" troubleshooting functionality. It usually takes a couple seconds from the publisher to the distributor and a couple more from the distributor to the subscriber.

I guess my question is actually whether it is possible to achieve sub-second (milliseconds) latency for transactional replication under any circumstances. Someone on another forum told me it was not, so I thought I would ask a separate community to confirm. Regarding the hardware, the latency on ping is less than 1ms between the servers and the servers themselves are decently powered quad processor boxes w/ 4GB of ram each. It seems to have the same latency of 3-5 seconds regardless of whether I publish a single table or all of the tables in the database. I currently have it configured with the publisher on one server and the distributor/subscriber on the second with the log reader and distributor agents set to run continuously. If it is possible, please recommend configuration of the agents or the topology of the PDS to achieve this. Thanks in advance for any insight you provide.

Dan

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Transactional Replication - Performance And Troubleshooting

Feb 25, 2004

Hi

I have sucessfully set up transactional replication, allowing the subscriber to update the publisher. All works well for a while, but after a couple of weeks or so it fails, but always for a different reason !

My question is, is there anything that can be done to help replication stay healthy. I had thought of doing regular backups of the database and the transaction log, and then truncating the transaction log.

Any advice, or links to other troubleshooting resource much appreciated.