Today’s script is to help replication performance. It was something I learned from my resident replication expert Paul Anderton. Below is a description of virtual subscriptions.
If Immediate_Sync is set when a publication is created then virtual subscriptions can occur. These can affect the "Distribution Clean Up: distribution" SQL job and the "msrepl_commands" table. By Default the job runs every 10 mins and removes replicated commands from the "msrepl_commands" table dependant on the @min_distretention value (0 hrs is default). If virtual subscriptions are present then the @min_distretention value is ignored and all replicated commands will only be removed after the @max_distretention is reached (72 hrs is default).
This script is one I have run on all my servers serving as a distributor to remove the virtual subscribers. The performance gain in all instances is fantastic the distribution clean up job runs a lot faster and replication latency (number of undistributed commands) is dramatically reduced.
/*
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Remove Virtual Subscriptions
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For more SQL resources, check out SQLServer365.blogspot.com
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You may alter this code for your own purposes.
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You must obtain prior permission before blogging this code.
THIS CODE AND INFORMATION ARE PROVIDED "AS IS"
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*/
-- Set database context
USE distribution;
GO
-- Get undelivered commands
SELECT
*
FROM
MSdistribution_status
ORDER BY
UndelivCmdsInDistDB DESC
-- Check for virtual subscriptions
SELECT
msp.publication,
mss.publisher_db,
mss.publication_id,
mss.subscriber_id,
mss.subscriber_db,
mss.subscription_type,
mss.[status]
FROM
distribution.dbo.MSsubscriptions mss
left join distribution.dbo.MSpublications msp ON mss.publication_id = msp.publication_id
GROUP BY
msp.publication,
mss.publisher_db,
mss.publication_id,
mss.subscriber_id,
mss.subscriber_db,
mss.subscription_type,
mss.[status];
GO
-- Remove virtual subscriptions
DECLARE @minid INT
DECLARE @maxid INT
DECLARE @pubname VARCHAR(100)
DECLARE @pubdb VARCHAR(100)
SELECT
@minid = MIN(mss.publication_id),
@maxid = MAX(mss.publication_id)
FROM
distribution.dbo.MSsubscriptions mss
INNER JOIN distribution.dbo.MSpublications msp ON mss.publication_id = msp.publication_id
WHERE
mss.subscriber_db = 'virtual'
WHILE @minid <= @maxid
BEGIN
SELECT
@pubname = msp.publication,
@pubdb = mss.publisher_db
FROM
distribution.dbo.MSsubscriptions mss
INNER JOIN distribution.dbo.MSpublications msp ON mss.publication_id = msp.publication_id
WHERE
mss.subscriber_db = 'virtual'
AND mss.publication_id = @minid
EXEC ('
EXEC ' + @pubdb + '.dbo.sp_changepublication
@publication = ' + @pubname + ',
@property = ''allow_anonymous'',
@value = ''false'' ;
')
EXEC ('
EXEC ' + @pubdb + '.dbo.sp_changepublication
@publication = ' + @pubname + ',
@property = ''immediate_sync'',
@value = ''false'' ;
')
SELECT
@minid = MIN(mss.publication_id)
FROM
distribution.dbo.MSsubscriptions mss
inner join distribution.dbo.MSpublications msp ON mss.publication_id = msp.publication_id
WHERE
mss.subscriber_db = 'virtual'
AND mss.publication_id > @minid
END;
GO
-- Check for virtual subscriptions
SELECT
msp.publication,
mss.publisher_db,
mss.publication_id,
mss.subscriber_id,
mss.subscriber_db,
mss.subscription_type,
mss.[status]
FROM
distribution.dbo.MSsubscriptions mss
left join distribution.dbo.MSpublications msp ON mss.publication_id = msp.publication_id
GROUP BY
msp.publication,
mss.publisher_db,
mss.publication_id,
mss.subscriber_id,
mss.subscriber_db,
mss.subscription_type,
mss.[status];
GO
Enjoy!
Chris
