By fault 10 related items per POST request can be handled. By default if there are 11 items in the indexing request; the last item is silently ignored (a warning is output in the logs). The below are the properties that are available for configuration, for adjusting these defaults
* related-item.max.number.related.items.per.index.request = 10 * related-item.max.related.item.post.data.size.in.bytes = 10240 * related-item.indexing.discard.storage.requests.with.too.many.relations = false
The answer to this question is that you can have as many properties as you like per indexed relate item. However, in order to have as many items as you like you need to pay for that, in terms of memory allocated to the application, or reduction in the ring buffer size, and or length of the property keys/values.
The following properties are available for configuration, show with their defaults. As a result if you know a related item will have more than 10 properties (remember this leaves you with 7 configurable properties of your choosing; id, date and related-with take already taken)
* related-item.max.number.related.item.properties = 10 * related-item.additional.prop.key.length = 30 (characters) * related-item.additional.prop.key.length = 30 (characters) * related-item.indexing.size.of.incoming.request.queue = 16384