With index capacity now increasing up to 250 million index items spanning 64 components in a search farm, many customers are looking for partial results feature. Essentially customers are looking for an ability to mitigate “full search outage” situation in large scale SharePoint search farm when some of search components are still working fine. This feature would allow customers to enable their end users to receive a partial result set even if not all replicas have responded to a query. This is also very helpful in significantly reducing the probability of search outages when customers deploy large number of partitions (we allow up to 25 partitions). This feature would also allow customers to provide some guaranteed minimum SLA to its end users for mission critical search portals in SharePoint. Below are some specifics
WHAT IS CHANGED?
We introduced a new search setting on SSA level (AllowPartialResults) as one central switch to turn on/off (default) the partial results feature on farm level. After enabling this feature, if one of the search replicas is degraded, end users will still receive results from available search components. All relevancy and refinement results are returned from those available / responding index partitions (cells). Each and every returned result will have complete summary info for consistent UI rendering. When you enable this feature, a new metadata property is added in ResultTableCollection (PartialResults = true) only when partial results are returned in the backend. CSOM / REST API would also pick up this new property automatically after Server OM has been changed.
HOW TO ENABLE FEATURE?
This feature can be enabled through below steps
# Make sure you are on NOV 2014 CU
# Once ensuring above, to enable this feature, please do the following:
$ssa.AllowPartialResults = $true
Please note that we won’t support enabling this feature on site collection / site level - once turned on in SSA, this feature will affect all search sites.