7

As far as I understand it, XPM preview doesn't read or write anything to or from the main broker database - so there should be no need to have to configure the broker database in the cd_storage_conf.xml file of the Preview web service.

However, every example I've seen has both a preview database and a broker database configured. Is this just a cargo cult thing, or is there a real reason to have both?

7

XPM does read from both databases. We can deduce this because the Staging website has 2 modes:

  • XPM disabled - uses regular DB
  • XPM enabled - uses Session Preview DB

So it is not just a "cargo cult thing."

We can also see from the debug logs that XPM does some interesting triaging between the regular Broker and the Session Preview Broker:

2014-12-11 16:46:24,070 DEBUG ReadMethodHandler - Invoking read method: getPageURL on DAO: com.tridion.storage.persistence.JPAItemDAO@569bfd69
2014-12-11 16:46:24,070 DEBUG AbstractMethodHandler - Original publication ID for write method parameter [non_entity] is 10.
2014-12-11 16:46:24,070 DEBUG AbstractMethodHandler - Session-publication ID for write method parameter [non_entity] is 8.
2014-12-11 16:46:24,071 DEBUG ReadMethodHandler - Session DAO did not return a result, invoking original DAO method: getPageURL.

So it appears that when XPM is turned on on a given page, it stores and loads the items that are being session-previewed from the Session Preview DB and the items that don't need to be re-rendered come from the regular Broker and it merges the results from the two DBs.

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  • 1
    That's indeed exactly what I recall Nick: the Session Preview DB acts as an overlay over the regular broker DB for your preview session. – Frank van Puffelen Dec 11 '14 at 21:24
  • Indeed, the staging web application (or the filter/module) needs to read from both. The question is specifically about the configuration of the web service. And there, my "cargo cult" question still stands. – Dominic Cronin Dec 12 '14 at 8:12
  • Just tried setting the cd_preview_webservice without the main broker storage type. It throws an error, "Storage not available: No Data Access Object Factory" upon accessing a page in XPM mode. – Nickoli Roussakov Dec 12 '14 at 15:11
  • You have to have a defaultStorageId, and I think it needs to point to a storage. (And a storage in a wrapper doesn't seem to count.) I've got it running with a filesystem storage pointing to NUL, but I don't know if there are use cases where it might break, or why. – Dominic Cronin Dec 13 '14 at 8:20
3

The "preview webservice" as you call it is the regular Content Delivery Web Service (sometimes also referred to as the "OData service") and it does (potentially) a lot more then just deploy session preview content to XPM:

  • access FredHopper system configuration for SmartTarget
  • access broker content via OData
  • likely a hell of a lot more in the future seeing where things are going (note that this is more of a gut feeling from my side than anything confirmed by SDL R&D)

If in your scenario you are interested solely in serving deploying session preview content for XPM you will not need the configuration for the broker database; whether the software will work without it is an entirely different question (to my knowledge the preview webservice needs a correctly configured cd_deployer_conf.xml even though it does not do regular deployments but who knows how all of it works under the hood of the public API? Certainly not me anyway )

Long story short: if you don't need it try without it but remember that is is generally riskier to lead then to follow...

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    Heard a rumour that the deployer config is needed because of the TCDL transforms (which must then presumably be executed as the content is stored in the preview database). – Dominic Cronin Dec 12 '14 at 13:48
  • Ah yes of course! Is this used even when the target language is REL and no deploy time transformations take place? – Bjørn van Dommelen Dec 12 '14 at 14:28

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