Proactive Caching and Real-Time Updates - Microsoft SQL Server 2008 Analysis Services - page 435

Caching object solves this problem with its SilenceInterval and SilenceOverride
Interval properties:

. The SilenceInterval property specifies the amount of time, after it receives a notifi-

cation, that Analysis Services waits before it starts building a new version of the
object— quiet time . If Analysis Services receives another notification during quiet
time, it just ignores it. The default value -1 (infinite) means ignore notifications .

. The SilenceOverrideInterval property specifies the time after which Analysis

Services starts to process a new version of the object, even if updates come so fre-
quently that there is no quiet time, as defined by the SilenceInterval property.
The SilenceOverrideInterval property ensures that the object eventually will be
updated, regardless of the stream of updates. The default value -1 (infinite) means
no override .

Long-Running MOLAP Cache Processing

In cases where processing of the MOLAP cache takes a long time, you might prefer to sacri-
fice performance in favor of reducing latency (MOLAP to ROLAP to MOLAP mode of proac-
tive caching). Proactive caching provides a Latency property to define how much time
should pass after notification and before the storage mode of the object is switched from
MOLAP to ROLAP. The default behavior -1 (infinite) means never revert to ROLAP mode .

Two additional properties, OnlineMode and AggregationStorage , control how an object
behaves when it is converted to ROLAP:

. The OnlineMode property specifies whether to allow users to query dimensions or

partitions while the object is in ROLAP mode. It takes two values: Immediate and
OnCacheComplete .

. With OnlineMode set to Immediate , a user can query the object immediately

after it changed to ROLAP; queries are resolved from the ROLAP storage.

. With OnlineMode set to OnCacheComplete , a user can't query the object until

the MOLAP cache is built. If the time set by the Latency property has expired,
the object is temporarily unavailable for query by users. The default value is
Immediate . Be careful setting this property to Immediate on a Dimension object.
You don't want it to change to ROLAP mode, because you would lose data in
your MOLAP partitions.

. The AggregationStorage property defines whether Analysis Services creates (or starts

using existing) ROLAP aggregations when a partition is switched to ROLAP mode.
AggregationStorage takes one of two values: Regular or MolapOnly .

. When you set AggregationStorage to Regular , Analysis Services converts the

Partition object to ROLAP mode, but builds ROLAP aggregations (creates
indexed views in SQL Server).

. When you set AggregationStorage to MolapOnly , Analysis Services doesn't

create ROLAP aggregations.