The "Pre-Aggregated Reports" use case doc page http://docs.mongodb.org/ecosystem/use-cases/pre-aggregated-reports/ is one of the most important use case pages for MongoDB, and is used and reference by many customers/users, especially w.r.t. to time-series type usage patterns, often found in Financial Services and IoT.

With the introduction of WiredTiger in MongoDB version 3.0, some of the advice in this page may no longer be applicable and may need to be marked as applying to MMAPv1 use only.

The page defines 4 key patterns:
1. Pre-aggregation (update averages/mins/maxs for each consumed event rather than recording raw event).
2. Bucketing (grouping sets of records together, eg. by day, for fast subsequent access - the pattern to deal with consuming lots of fine grained events and then servicing analytics/reports that want to retrieve coarse grained data).
3. Pre-allocation (aka. pre-padding, to avoid excessive document growth and re-allocation)
4. Intra-document-hierarchy (to prevent event ingestion latencies from increasing as the time of each day increases)

Note: These patterns are also documented in chapter 4 of the book "MongoDB Applied Design Patterns" by Rick Copeland (O'Reilly)

With the introduction of WiredTiger, it is likely that pattern 3 (Pre-allocation) is no longer required and perhaps would even be detrimental, due to the way WiredTiger deals with "in-place updates" internally. Also it could be that pattern 4 (intra-document hierarchy) also adds no value when using WiredTiger (this needs to be validated by someone).

Please update the doc page to indicate which of the 4 patterns should not be applied, when running WiredTiger rather than MMAPv1.