Answer / bidhar

CDC is used when you want to pull the records which have
changed or newly added in the OLTP system.

Normally the OLTP tables have 2 columns
last_updated_timestamp and Added_timstamp.

Whenever a new record is added for the first time in these
tables then both the columns have the same timestamp ie
System timestamp.

Then when that particular record is changed only the column
last_updated_timestamp will change and the other column
Added_timstamp will remain same forever.

Now you need to pull this record when it was added as well
as when it was modified to keep your warehouse in sync with
OLTP system.

So based on last_updated_timestamp column (not
Added_timstamp)you need to pull the records.

This can be achieved by overriding the SQ query in the
where clause.

Example :- if product table in OLTP has 2000 records on
11th may and on 12th may 10 new records have come up and 5
records have been changed.Then in the next load 15 records
should be pulled to your warehouse.

Select Prd_nam,Typ,grp,category from product where
last_updated_timestamp>&&date_parameter

This is your SQ override query.
&&date_parameter is a mapping parameter which can be picked
up from a file.(you need to have the previous load max date
in that file which will be used as mapping parameter).

Hope this clears your doubt.

Answer / infa developer

Not always necessary to be a Date field. When there are 5
key colummns and you want to check if any of them changed
and would like to extract only those records with these 5
key column values updated then you will have use this
concept of change data capture.

Answer / vaibhav bhandeo

CDC stands for change data capture. This is used to
implement incremental load approach in data warehouse.
In this approach we traditionally keep a date field and
pull data on incremental date values.
This assures that we are picking latest data (Or may be new
batch data which ever is applicable).
Implementing this in mapping would require you to use
parameter files which will keep HiWaterMark and LoWatermark
which is repeatedly used to capture fresh data.

Answer / satya

CDC defines Whenever data is changed in OLTP Systems Only
that data Will be captured and loaded into our Target
SCD's works internally based on cdc logic
basically cdc's implented by using effective date

Answer / sreekanth

CDC stands for change data capture
Daily several transaction may happen among those some may
adds new records to the OLTP and some transaction updates
the existing so we need to capture the changes then while
loading the data we need to update on the existing date ware
house with changes made to OLTP for this we will maintains
when created and when updated audit column in OLTP according
those fields we can load the data to targt.

Answer / mike

capturing only changes is ok.. but in realtime as soon as the data changes in the source ... changes should be implmented in the target... so how's z dat done ? means hw we will know that source rows have been changed(suppose like evy 15 mins)? do we need to run the run mapping for evy 15mins? how does CDC works actually? i would really appreciate if some one can explain me?

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