CDC and deferred updates

Question

I am using CDC to generate events based on the entries in the CDC tables. I need to distingush between insert, update and delete events but when SQL chooses to do a deferred update, it changes an update into a delete and insert - is there a way I can affect
this behaviour so that any update command results in an update record in the cdc tables?
I am aware of the DBCC TRACEON (8207,-1) but this seems to only apply to update commands affecting 1 record and which don't affect fields used by unique constraints - my update commands will affect multiple records and fields with unique constraints applied
to them.

Answer 1

This problem is caused by a bug in the fn_cdc_get_net_changes_<capture_instance> functions. The bug works in 2 ways, the first is indentified in this thread: an additional row is exported with __$operation = 1. A 2nd problem, resulting from the same
bug, is that some rows with __$operation = 1 are incorrectly suppressed. These missing rows are however less easily spotted and thus this incarnation of the problem is nowhere reported.
The bug is reported on Connect as
ID 690476 back in 2011 already. Below is a copy of the corrected cdc.fn_get_net_changes_dbo_NETTEST function in my test database. The fix can easily be extracted from this sample code. I would suggest you do not adapt the functions yourself in a production
environment. Instead we should put all our combined powers in to get Microsoft to fix this issue. Please Vote and if possible have the case reopened as soon as possible. 
create function [cdc].[fn_cdc_get_net_changes_dbo_NETTEST]
( @from_lsn binary(10),
@to_lsn binary(10),
@row_filter_option nvarchar(30)
returns table
return
select NULL as __$start_lsn,
NULL as __$operation,
NULL as __$update_mask, NULL as [ID], NULL as [A]
where ( [sys].[fn_cdc_check_parameters]( N'dbo_NETTEST', @from_lsn, @to_lsn, lower(rtrim(ltrim(@row_filter_option))), 1) = 0)
union all
select __$start_lsn,
case __$count_23BAE034
when 1 then __$operation
else
case __$min_op_23BAE034
when 2 then 2
when 4 then
case __$operation
when 1 then 1
else 4
end
else
case __$operation
when 2 then 4
when 4 then 4
else 1
end
end
end as __$operation,
null as __$update_mask , [ID], [A]
from
select t.__$start_lsn as __$start_lsn, __$operation,
case __$count_23BAE034
when 1 then __$operation
else
( select top 1 c.__$operation
from [cdc].[dbo_NETTEST_CT] c with (nolock)
where ( (c.[ID] = t.[ID]) )
and ((c.__$operation = 2) or (c.__$operation = 4) or (c.__$operation = 1))
and (c.__$start_lsn <= @to_lsn)
and (c.__$start_lsn >= @from_lsn)
order by c.__$seqval) end __$min_op_23BAE034, __$count_23BAE034, t.[ID], t.[A]
from [cdc].[dbo_NETTEST_CT] t with (nolock) inner join
( select r.[ID], max(r.__$seqval) as __$max_seqval_23BAE034,
count(*) as __$count_23BAE034
from [cdc].[dbo_NETTEST_CT] r with (nolock)
where (r.__$start_lsn <= @to_lsn)
and (r.__$start_lsn >= @from_lsn)
group by r.[ID]) m
on t.__$seqval = m.__$max_seqval_23BAE034 and
( (t.[ID] = m.[ID]) )
where lower(rtrim(ltrim(@row_filter_option))) = N'all'
and ( [sys].[fn_cdc_check_parameters]( N'dbo_NETTEST', @from_lsn, @to_lsn, lower(rtrim(ltrim(@row_filter_option))), 1) = 1)
and (t.__$start_lsn <= @to_lsn)
and (t.__$start_lsn >= @from_lsn)
and ((t.__$operation = 2) or (t.__$operation = 4) or
((t.__$operation = 1) and not exists (
select top(1) *
from [cdc].[dbo_NETTEST_CT] c with (nolock)
where ( (c.[ID] = t.[ID]) )
and c.__$operation = 2
and c.__$start_lsn = t.__$start_lsn
and c.__$seqval = t.__$seqval
--(2 not in
-- ( select top 1 c.__$operation
-- from [cdc].[dbo_NETTEST_CT] c with (nolock)
-- where ( (c.[ID] = t.[ID]) )
-- and ((c.__$operation = 2) or (c.__$operation = 4) or (c.__$operation = 1))
-- and (c.__$start_lsn <= @to_lsn)
-- and (c.__$start_lsn >= @from_lsn)
-- order by c.__$operation desc
and t.__$operation = (
select
max(mo.__$operation)
from
[cdc].[dbo_NETTEST_CT] as mo with (nolock)
where
mo.__$seqval = t.__$seqval
and
( (t.[ID] = mo.[ID]) )
group by
mo.__$seqval
) Q
union all
select __$start_lsn,
case __$count_23BAE034
when 1 then __$operation
else
case __$min_op_23BAE034
when 2 then 2
when 4 then
case __$operation
when 1 then 1
else 4
end
else
case __$operation
when 2 then 4
when 4 then 4
else 1
end
end
end as __$operation,
case __$count_23BAE034
when 1 then
case __$operation
when 4 then __$update_mask
else null
end
else
case __$min_op_23BAE034
when 2 then null
else
case __$operation
when 1 then null
else __$update_mask
end
end
end as __$update_mask , [ID], [A]
from
select t.__$start_lsn as __$start_lsn, __$operation,
case __$count_23BAE034
when 1 then __$operation
else
( select top 1 c.__$operation
from [cdc].[dbo_NETTEST_CT] c with (nolock)
where ( (c.[ID] = t.[ID]) )
and ((c.__$operation = 2) or (c.__$operation = 4) or (c.__$operation = 1))
and (c.__$start_lsn <= @to_lsn)
and (c.__$start_lsn >= @from_lsn)
order by c.__$seqval) end __$min_op_23BAE034, __$count_23BAE034,
m.__$update_mask , t.[ID], t.[A]
from [cdc].[dbo_NETTEST_CT] t with (nolock) inner join
( select r.[ID], max(r.__$seqval) as __$max_seqval_23BAE034,
count(*) as __$count_23BAE034,
[sys].[ORMask](r.__$update_mask) as __$update_mask
from [cdc].[dbo_NETTEST_CT] r with (nolock)
where (r.__$start_lsn <= @to_lsn)
and (r.__$start_lsn >= @from_lsn)
group by r.[ID]) m
on t.__$seqval = m.__$max_seqval_23BAE034 and
( (t.[ID] = m.[ID]) )
where lower(rtrim(ltrim(@row_filter_option))) = N'all with mask'
and ( [sys].[fn_cdc_check_parameters]( N'dbo_NETTEST', @from_lsn, @to_lsn, lower(rtrim(ltrim(@row_filter_option))), 1) = 1)
and (t.__$start_lsn <= @to_lsn)
and (t.__$start_lsn >= @from_lsn)
and ((t.__$operation = 2) or (t.__$operation = 4) or
((t.__$operation = 1) and not exists (
select top(1) *
from [cdc].[dbo_NETTEST_CT] c with (nolock)
where ( (c.[ID] = t.[ID]) )
and c.__$operation = 2
and c.__$start_lsn = t.__$start_lsn
and c.__$seqval = t.__$seqval
--(2 not in
-- ( select top 1 c.__$operation
-- from [cdc].[dbo_NETTEST_CT] c with (nolock)
-- where ( (c.[ID] = t.[ID]) )
-- and ((c.__$operation = 2) or (c.__$operation = 4) or (c.__$operation = 1))
-- and (c.__$start_lsn <= @to_lsn)
-- and (c.__$start_lsn >= @from_lsn)
-- order by c.__$operation desc
and t.__$operation = (
select
max(mo.__$operation)
from
[cdc].[dbo_NETTEST_CT] as mo with (nolock)
where
mo.__$seqval = t.__$seqval
and
( (t.[ID] = mo.[ID]) )
group by
mo.__$seqval
) Q
union all
select t.__$start_lsn as __$start_lsn,
case t.__$operation
when 1 then 1
else 5
end as __$operation,
null as __$update_mask , t.[ID], t.[A]
from [cdc].[dbo_NETTEST_CT] t with (nolock) inner join
( select r.[ID], max(r.__$seqval) as __$max_seqval_23BAE034
from [cdc].[dbo_NETTEST_CT] r with (nolock)
where (r.__$start_lsn <= @to_lsn)
and (r.__$start_lsn >= @from_lsn)
group by r.[ID]) m
on t.__$seqval = m.__$max_seqval_23BAE034 and
( (t.[ID] = m.[ID]) )
where lower(rtrim(ltrim(@row_filter_option))) = N'all with merge'
and ( [sys].[fn_cdc_check_parameters]( N'dbo_NETTEST', @from_lsn, @to_lsn, lower(rtrim(ltrim(@row_filter_option))), 1) = 1)
and (t.__$start_lsn <= @to_lsn)
and (t.__$start_lsn >= @from_lsn)
and ((t.__$operation = 2) or (t.__$operation = 4) or
((t.__$operation = 1) and not exists (
select top(1) *
from [cdc].[dbo_NETTEST_CT] c with (nolock)
where ( (c.[ID] = t.[ID]) )
and c.__$operation = 2
and c.__$start_lsn = t.__$start_lsn
and c.__$seqval = t.__$seqval
--(2 not in
-- ( select top 1 c.__$operation
-- from [cdc].[dbo_NETTEST_CT] c with (nolock)
-- where ( (c.[ID] = t.[ID]) )
-- and ((c.__$operation = 2) or (c.__$operation = 4) or (c.__$operation = 1))
-- and (c.__$start_lsn <= @to_lsn)
-- and (c.__$start_lsn >= @from_lsn)
-- order by c.__$operation desc
and t.__$operation = (
select
max(mo.__$operation)
from
[cdc].[dbo_NETTEST_CT] as mo with (nolock)
where
mo.__$seqval = t.__$seqval
and
( (t.[ID] = mo.[ID]) )
group by
mo.__$seqval
SQL expert for JF Hillebrand IT BV - The Netherlands.