I don't entirely understand the purpose of control flow in an SSIS package. In all of the packages I've created, I simply add a data flow component to control flow and then the rest of the logic is located within the data flow.
I've seen examples of more complicated control flows (EX: foreach loop container that iterates over lines in an Excel file.), but am looking for an example where it could not also be implemented in the data flow. I could just as easily create a connection to the excel file within the data flow.
I'm trying to get a better understanding of when I would need to (or should) implement logic in control flow vs using the data flow to do it all.
What prompted me to start looking into control flow and it's purpose is that I'd like to refactor SSIS data flows as well as break packages down into smaller packages in order to make it easier to support concurrent development.
I'm trying to wrap my mind around how I might use control flow for these purposes.
A data flow defines a flow of data from a source to a destination. You do not start on one data flow task and move to the next. Data flows between your selected entities (sources, transformations, destinations).
Moreover within a data flow task, you cannot perform tasks such as iteration, component execution, etc.
A control flow defines a workflow of tasks to be executed, often a particular order (assuming your included precedence constraints). The looping example is a good example of a control-flow requirement, but you can also execute standalone SQL Scripts, call into COM interfaces, execute .NET components, or send an email. The control flow task itself may not actually have anything whatsoever to do with a database or a file.
A control flow task is doing nothing in itself TO the data. It is executing some that itself may (or may not) act upon data somewhere. The data flow task IS doing something with data. It defines its movement and transformation.
It should be obvious when to execute control flow logic and data flow logic, as it will be the only way to do it. In your example, you cite the foreach container, and state that you could connect to the spreadsheet in the data flow. Sure, for one spreadsheet, but how would you do it for multiple ones in a folder? In the data flow logic, you simply can't!
Hope this helps.
Data flow - are for just moving data from one source to another.
Control flow - provide the logic for when data flow components are run and how they are run. Also control flow can: perform looping, call stored procedures, move files, manage error handling, check a condition and call different tasks (incl data flows) depending on the result, process a cube, trigger another process, etc.
If you're moving data from one location to another and it's the same each time, not based on any other condition, then you can get away with a package with just a dataflow task, but in most cases packages are more complex than that.
We use the control flow for many things. First all our data concerning the data import is stored in tables. So we run procs to start the dataflow and end it, so that our logging works correctly, we do looping through a set of files, we move files to archive locations and rename with the date and delete them from processing locations. We have a separate program that does file movement and validates the files for the correct comlumns and size. We run a proc to make sure the file has been validated before going into the dataflow. Sometimes we have a requirement to send an email when a file is processed or send a report of records which could not process. These emails are put into the control flow. Sometimes we have some clean up steps that are more easily accomplished using a stored proc and thus put the step in the control flow.
Trying to give a basic answer - Control Flow performs operations; such as executing a SQL Statement or Sending an email. When a control flow is complete, it either failed or succeeded.
Data flow on the other hand is found on container flow items and offers ability to move, modify and manipulate data.
Related
I have a Data Flow with OLE DB Source, Script Component (Transformation), and Flat File Destination:
The OLE DB Source task has 100+ columns. The script component is going to cleanup data in each column and then output it to the Flat File Destination.
Adding output columns by hand in Script Component is unthinkable to me.
What options do I have to mirror the output columns with the input columns in the Script Component? While the output column name will be the same, I plan to change the datatype from DT_STR to DT_WSTR.
Thank you.
You are short of luck here. Possible scenarios:
Either you use Script Component and have to key in all columns and its properties manually. In your case, you have to set proper datatype.
Or you can create your own Custom Component which can be programmed to create output columns based on input columns. It is not easy and I cannot recommend a simple guideline, but it could be done.
This might have sense if you have to repeat similar operations in many places so it is not a one-time task.
You can create a BIML script that creates a package based on metadata. However, the metadata (list of columns and its datatypes) has to be prepared before running BIML script or do some tricks to get it during script execution. Again, some proficiency with BIML is essential.
So, for one-time job and little experience with BIML I would go for a pure manual approach.
I have a weird problem with Foreach Loop Container.
I have a package to take backup of out SSAS cubes. We have both UDM and Tabular cubes. Considering below figure, based on a variable, flow should go to Find UDM Cubes OR Find TAB Cubes, so I used Expression in Constrains (connections)
With one specific parameter, the flow should go trough Find UDM Cubes and with a different parameter, flow should go through Find TAB Cubes.
When testing, I noticed that the the package is not doing as expected and the Script Task is not executing. If I remove one of the highlighted Constraints (connection), Script Tasks get hit and works. So as long as I have ONE input for the Script Task it works otherwise it just not do anything.
Appreciate if anybody can help.
Multiple Precedence Constraints
Both of your Data flow Tasks would have to succeed in order for the script task to run. Which you are stating that both data flows may not even execute so therefore both don't succeed.
here is a nice article on it https://msdn.microsoft.com/en-us/library/ms139895.aspx
One way to get your desired behavior would be to add a sequence container and move your clean up and find tasks into it and then create the precedence from the sequence container to your script task. That way even if only 1 runs everything is still considered successful and your script task should execute.
this precedence suggestion has been tested and works.
I am using SSIS for data warehousing to import data from different sources like flat files,.xls and some other SQL server servers.
In my scenario i have 50 data flow task which execute in a package(Control flow) parallel.These data flow are independent means fetching data from different tables and files into my warehouse DB.
In my case sometime structure of my source table or file changed and then my package got failed means show validation error.
I need a solution by which I can skip only corrupted "data flow task" and other data flow task can complete their task. I don't like to make separate package for each data flow task.
Please advise what to do in such situation.
Regards
Shakti
I highly advise putting each of these into a separate package, and then using a scheduling tool or master package to call each one individually. It will make the maintainability of this solution much better.
If you insist on having them all in one package, you can use the "FailParentOnFailure", "FailPackageOnFailure", and "MaximumErrorCount" properties to have your data flow fail, but the container ignore errors, allowing other things to run. Really probably shouldn't do that though - failures could be for any number of reasons and having separate packages that run in parallel makes finding the error during a scheduled run much easier...
I have an SSIS data flow task that reads a CSV file with certain fields, tweaks it a little and inserts results into a table. The source file name is a package parameter. All is good and fine there.
Now, I need to process slightly different kind of CSV files with an extra field. This extra field can be safely ignored, so the processing is essentially the same. The only difference is in the column mapping of the data source..
I could, of course, create a copy of the whole package and tweak the data source to match the second file format. However, this "solution" seems like terrible duplication: if there are any changes in the course of processing, I will have to do them twice. I'd rather pass another parameter to the package that would tell it what kind of file to process.
The trouble is, I don't know how to make SSIS read from one data source or another depending on parameter, hence the question.
I would duplicate the Connection Manager (CSV definition) and Data Flow in the SSIS package and tweak them for the new file format. Then I would use the parameter you described to Enable/Disable either Data Flow.
In essence, SSIS doesnt work with variable metadata. If this is going to be a recurring pattern I would deal with it upstream from SSIS, building a VB / C# command-line app to shred the files into SQL tables.
You could make the connection manager push all the data into 1 column. Then use a script transformation component to parse out the data to the output, depending on the number of fields in the row.
You can split the data based on delimiter into say a string array (I googled for help when I needed to do this). With the array you can tell the size of it and thus what type of file it is that has been connected to.
Then, your mapping to the destination can remain the same. No need to duplicate any components either.
I had to do something similar myself once, because although the files I was using were meant to always be the same format - depending on version of the system sending the file, it could change - and thus by handling it in a script transformation this way I was able to handle the minor variations to the file format. If the files are 99% always the same that is ok.. if they were radically different you would be better to use a separate file connection manager.
I'd like to pass a Data Flow from one package to another for the following reasons:
It would help in refactoring common
logic in SSIS packages.
It would enable concurrent
development of larger SSIS packages.
At first glance, the Execute Package Task sounded promising, but it looks like I can only pass fairly simple variables in and out of the package.
Is there a way to do this using SSIS?
cozyroc.com is a third party tool that can do this I believe.
A bit of clarity Paul, are you talking about 1) code reusability or 2) allowing the results from one DFT to be used in another DFT?
The first you can't do in "native" SSIS I believe - a set of DFT modules that you can call from other packages, but I would approach it as building a set of packages that are quite simple
initialision routines
DFT
cleanup
Then having variables passed to the child package that are (e.g.) table to be processed, variable(s) to be selected from the source table.
It would requrie a very clever schema and some clever thinking about what the common DFT would do. But I think it would be possible.
The second is not possible without jumping through a few hoops - like saving result sets to temporary tables then re-reading the tables into later DFTs, but then you would loose the data actually flowing through the task.