Inserts in Merge Replication database are insanely slow

Question

I have a SQL server that is setup with merge replication to 800 mobile clients running SQL CE.

The server has enough resources and the lines in and out of the company are more than adequate, the replication between clients and the server is generally good but we are getting an intermittent error that I just cannot track down.

Yesterday we needed to insert 550 records into one of our main tables, the only triggers that exist are the standard merge replication ones.

This insert took 14 hours due to it continually getting deadlocked with mobile devices trying to synch.

Does anyone have any advice on how we can avoid locks on inserts and how to speed up the entire process?

------ Update -----

Following on from some comments I've run a profiler over a single insert and I'm seeing a lot of this sort of thing

insert into dbo.MSmerge_current_partition_mappings with (rowlock) (publication_number, tablenick, rowguid, partition_id)
            select distinct 1, mc.tablenick, mc.rowguid, v.partition_id
            from dbo.MSmerge_contents mc with (rowlock) 
            JOIN dbo.[MSmerge_JEMProjectME_PromotionResource_PARTITION_VIEW] v with (rowlock) 
            ON mc.tablenick = 286358001
            and mc.rowguid = v.[rowguid]
            and mc.marker = @child_marker 
            and v.partition_id in (select partition_id from dbo.MSmerge_current_partition_mappings cpm with (rowlock) JOIN
                dbo.MSmerge_contents mc2 with (rowlock)
                ON cpm.rowguid = mc2.rowguid
                and mc2.marker = @marker)
            where not exists (select * from MSmerge_current_partition_mappings with (readcommitted, rowlock, readpast) where 
                publication_number = 1 and 
                tablenick = 286358001 and
                rowguid = v.[rowguid] and
                partition_id = v.partition_id)

For many tables that I'm not meant to be inserting into... could this be a clue?

Answer 1

we recently experienced the same behavior in our system which is quite simular to yours. The reason was massive amounts of data in msmerge_contents and msmsmerge_current_partition_mappings, and we noticed that it might be a missing index by looking at the number of rows read in SQL Profiler. (49 000 000 reads for a simple insert in one for the tables seemed a little much)

Solved 30 minutes ago by adding two indexes:

CREATE NONCLUSTERED INDEX [IX_MSmerge_current_partition_mappings_PERF1] ON [dbo].[MSmerge_current_partition_mappings] 
(
    [partition_id] ASC
)
INCLUDE ( [rowguid]) 


CREATE NONCLUSTERED INDEX [IX_msmerge_contents_PERF1] ON [dbo].[MSmerge_contents] 
(
    [marker] ASC
)
INCLUDE ( [rowguid])

I hope this can help you, it helped us lower the query time from 5 minutes to 10 seconds.

-- A couple of hours later...

My colleague found another index that further increased the performance by another 75%:

CREATE NONCLUSTERED INDEX [IX_MSmerge_current_partition_mappings_PERF2] ON [dbo].[MSmerge_current_partition_mappings] 
(
    [rowguid] ASC,
    [partition_id] ASC
)

Identify missing index You can use the following script to identify missing indexes, sorted with the one expected to increase performance most at the top (There are numerous such scripts circulating, this one was borrowed from http://www.sherbaz.com/category/sqlserver/)

SELECT  sys.objects.name
, (avg_total_user_cost * avg_user_impact) * (user_seeks + user_scans) AS Impact
,  'CREATE NONCLUSTERED INDEX ix_IndexName ON ' + sys.objects.name COLLATE DATABASE_DEFAULT + ' ( ' + IsNull(mid.equality_columns, '') + CASE WHEN mid.inequality_columns IS NULL 
                THEN ''  
    ELSE CASE WHEN mid.equality_columns IS NULL 
                    THEN ''  
        ELSE ',' END + mid.inequality_columns END + ' ) ' + CASE WHEN mid.included_columns IS NULL 
                THEN ''  
    ELSE 'INCLUDE (' + mid.included_columns + ')' END + ';' AS CreateIndexStatement
, mid.equality_columns
, mid.inequality_columns
, mid.included_columns 
    FROM sys.dm_db_missing_index_group_stats AS migs 
            INNER JOIN sys.dm_db_missing_index_groups AS mig ON migs.group_handle = mig.index_group_handle 
            INNER JOIN sys.dm_db_missing_index_details AS mid ON mig.index_handle = mid.index_handle AND mid.database_id = DB_ID() 
            INNER JOIN sys.objects WITH (nolock) ON mid.OBJECT_ID = sys.objects.OBJECT_ID 
    WHERE     (migs.group_handle IN 
        ( 
        SELECT     TOP (500) group_handle 
            FROM          sys.dm_db_missing_index_group_stats WITH (nolock) 
            ORDER BY (avg_total_user_cost * avg_user_impact) * (user_seeks + user_scans) DESC))  
        AND OBJECTPROPERTY(sys.objects.OBJECT_ID, 'isusertable')=1 
    ORDER BY 2 DESC , 3 DESC