Configuring the changeover percent

The changeover percent does not apply to push data sources.

What is the changeover percent?

There are many things that can go wrong when an update happens, which can result in your search index being incomplete.

The changeover percent provides a safety net for your updates which will prevent an updated index from being made live if the updated index has shrunk beyond an acceptable size.

Why is the changeover percent necessary?

The changeover percent sets the acceptable size for an updated index.

A percentage is calculated that takes the number of documents built in the current completed update (not yet live) and divides this by the number of documents in the currently live index.

This percentage is compared with the changeover percent and if it is determined that the new index has shrunk in size beyond the acceptable limit then the update will fail .

This check is necessary because non-push indexes gather and build a completely fresh index, and swap to this on completion.

If Funnelback cannot gather data (for example the Internet link went down while the update was running) then the new index will be missing a lot of documents.

This check prevents an update like this from being treated as successful.

the changeover percent check can also fail if you have defined any vital servers that don’t appear in the new index.

What is an acceptable value for the changeover percent?

An acceptable value for the changeover percent will depend on your content and how much change you expect.

The default is 50% - so an update will fail if the new index is 50% or less of the size of the currently live index.

A small changeover percent makes sense if you throw away everything in your index every day. This might happen if you have an index that only covers today’s content (e.g. today’s news items). In this scenario, the number of documents in your index from day to day is completely random.

A large changeover percent makes sense if you rarely remove any content from your index. For example, an archive could have a 100% changeover percent because it is expected that it will only ever increase in size.

For an average website, it’s expected that you’ll have a number of additions and deletions on a daily basis, with a general trend for your index to increase in size over time. For this scenario a changeover percentage of about 75% will be appropriate, adjusted for how your business operates.

Setting the changeover percent

The changeover percent is set in the data source configuration by setting the changeover_percent configuration key.

Overriding a changeover percent failure

Sometimes the changeover check will fail, but you still want to make the new index live.

This can happen if:

  • you have made a major revision to your website and removed or archived a lot of content (e.g. you’ve released a brand-new site).

  • you have made significant changes to your gatherer configuration that has the expected result of decreasing the number of gathered documents.

If your update has failed the changeover percent check you may be able to force the update to proceed.

  1. Check to see if your data source is updating. If an update has already started on your data source you will need to wait for the update to finish (with the same failure).

  2. If the data source is not updating you can force the views to swap. Select advanced update from the update panel for your data source, choose the swap live and offline view option and start the update.

  3. The update will run very quickly as Funnelback doesn’t need to gather or index any content, it just makes the unsuccessful index live.

If you are unhappy with the search after swapping the views and you want to roll back the change you can re-run the advanced update above to swap the live and offline views.