A good general rule is that batch processes are more efficient than single ones. There are many occasions where transactional entry points can just as easily be replaced by recurring batch ones; the trick is to consider how important the timing of a program action really is.

For example, if you want to create an Abandoned Cart program, instead of using a transactional program based on an event triggered by the cart abandonment, you can set up a recurring filter that checks daily for carts abandoned in the preceding 24 hours.

As a general rule:

• If your entry node is Target segment or Recurring filter:
  AC will batch your users, and the batch is processed as a whole, resulting in significant performance improvements.
• If your entry node is New contact or Data change:
  Even though these are transactional entry nodes, they can receive large batches of contacts at a time, so you should bear in mind your other registration methods or contact data update processes (see: Pay attention to imports, below).
• For all other entry nodes:
  Processing is performed on each contact individually, resulting in a heavier load on the system.

There are many cases where a Recurring filter entry node will have the same result as an External event node, but will perform far better. Ask yourself how critical it is that the email is triggered instantly, before you opt for a transactional email.

For example, you can trigger a shipping confirmation email using the External event node, but you can just as easily set a daily filter to return all contacts whose items have been shipped the previous day, and send a batch email.

If you set the Wait node to wait for 24 hours, each contact going through it will be processed individually. This means that for a busy program, this node could be running almost continuously, causing unnecessary load.

 Where possible, set it to wait for a specific time, e.g. "wait until tomorrow 10 am", so the node can process all the contacts together.

If you have multiple Wait nodes in a program, try to set each of them to a different time of day to spread the load. If you want to ensure that all the messages following these nodes are sent at the same time, use additional Wait nodes to compensate. In the example below, the filter Didn't respond to email will run at different times, but both of the reminder emails will be sent at 09:00.

Imports can inadvertently add contacts to programs that start with a New contact or Data change entry point, if they contain new registrations or a field defined in a Data change node.  

It is tempting to create one huge, complex program to cover an entire marketing strategy, but this really brings no benefits. If you create a number of smaller, less complex programs instead you can more easily identify where your strategy can be optimized and make your changes without affecting the other programs. Contacts can easily be passed from one program to another.

Contacts should only ever proceed along one path of a program. If you split paths, it is up to you to ensure that the filter logic excludes the possibility of a contact proceeding along more than one path.

If you rejoin paths after a split, we will not check for duplicates when the contacts reach the junction. It is therefore possible for a contact to appear twice on the same path, and receive the same messages twice.

There are some assets (forms, fields, messages, external events, etc.) that you can use in multiple live programs at the same time, and some that you can only use in one. These assets are checked for exclusivity only when the program using them is launched.

If you try to launch a program that uses an asset that is already selected in a node in another program, you will be informed of this and must de-select the asset in the nodes of the other program before you can launch the first program. 

Here is an overview of the rules concerning exclusive assets.

Exclusive

• Forms can only be used in one active program at a time.
• Emails can only be used in one active program, ever.
• New contact can be used as entry point for only one active program at a time.
• Fields may only be referenced by one Data change entry point at a time. You may have many programs starting with this node, but each must reference a different field.

Not exclusive 

• External events may be used in as many active programs as you like.
• All channels other than email (e.g. SMS, Mobile Engage, CRM Ads, Web Channel) support using the same message in more than one active program.  

As a rule, all emails sent via the Automation Center will respect the opt-in status of the recipient. However, an exception has been made for the following transactional entry points:

• Form
• External event

If you create a program that starts with one of these entry points, the first email in the program will be sent to all participating contacts regardless of their opt-in status (i.e. opt-in can be empty or FALSE).

This is to enable you to set up double opt-in programs, and critical transactional programs such as support requests, order and shipping confirmation, etc.

You can only enable STO in a program if its state is In design. You cannot turn STO on or off once the program's state has been changed from In design to another one.

To enable or disable STO in an active program, you have to pause or end it, then copy it to create a new program. Now you can turn STO on or off in the new program.

Remember that an automated program must use the same account resources as your other segments and emails, as well as the other programs.

• Avoid scheduling Wait nodes for high traffic hours when you are sending large email campaigns.
• Avoid scheduling Wait nodes for the same fixed time across multiple programs.
• Avoid scheduling many Recurring filters for the same fixed time.
• If possible, consider breaking  your complex program into 2-3 smaller programs (see: Connecting programs).

The settings you choose will have an important effect on the performance of your program.

• Contacts can enter the program anytime even if they are already in it is the least performance-heavy setting. You should use this whenever possible, and exclude the contacts you don't want to enter the program via a filter (based on whatever conversion criteria you are using).
• Contacts can enter this program only once ever has a high performance cost because every contact entering it must be checked to see if they have entered it before. You should use this only if it is absolutely necessary because for a program with a large number of contacts, referencing the program participation table could slow down any other programs using it.

Advanced Settings

In most cases batches are extremely fast. The only exception is when the advanced participation settings are used. These are:

• Contacts can enter this program immediately after exiting it
• Contacts can enter this program again X days and Y hours after exiting it

These settings mean that we have to keep track of each contact individually to know when they leave the program. For this reason, the Advanced participation settings have a high performance cost and should only be used when absolutely necessary.

Exit criteria place a segment node after the entry point and all Wait nodes. Depending on the complexity of your program, this could cause heavy load. In such cases you could consider using a filter switch before the channel nodes to exclude contacts.

The use of attachments in emails is not supported by the Automation Center. However, since they are supported by Triggered Email, you can send the attachment using that feature and then use the same external event to add the contact to a program to follow it up.

An issue to be aware of with all programs that spawn duplicate campaign names differentiated only by # numbers.

Campaigns with the same name can be found under analysis, because the naming convention creates a time stamp for campaigns without a second counter, and the system needs to differentiate with a hashtag and number. The resulting ambiguity can cause user confusion.

• All filter nodes reference your entire contact database, even if they are filtering for a single contact, so use them efficiently. 
• You should never run multiple filters sequentially; replace them with a single combined segment.
• Never place a filter immediately after a transactional entry node. Content should be personalized within the email where possible (see above). 
• Avoid having the same segment run more than once at the same time. For example, if you select a segment for the Exit criteria, this will run after every Wait node in the program, so make sure these are set for different times of the day.
• A segment can only be run by one program at a time, so if the same segment is referenced by multiple programs at the same time, the segment will be queued and processed program by program.  This also applies to Exit criteria. You can get around this by making copies of the segment and referencing a different copy in each program.
• Avoid running many Segment nodes in parallel, since all contacts must be processed by each one. Use a cascading set of Filter switches instead.

Since the program reporting shows the number of contacts returned by the filter nodes, you may be tempted to add additional filters at the end of paths just to see the number of contacts that end up there.

Not only does this cause unnecessary load on the program, but each filter reflects only one specific outcome and should not be relied upon as an accurate measure of your marketing strategy. 

You will get much more accurate and relevant reporting when you tie your customer engagement programs to your Smart Insight customer lifecycle reports.

For more information, see Automation Center - Program Reporting.