Database Reference
In-Depth Information
Storage Op-
tion
Explanation
Advantages
Drawbacks
Multi-Di-
mensional
OLAP
(MOLAP
)
This storage op-
tion stores data
in Microsoft's
proprietary,
highly com-
pressed format.
It offers superior
performance.
MOLAP storage
is used by the
majority of suc-
cessful SSAS
implementations.
Data must be read from the re-
lational database and written to
MOLAP structures. Hence data
is duplicated and users must
wait until processing is com-
plete and it is available for
querying.
Relational
OLAP
(ROLAP
)
This storage op-
tion retains data
in the relational
database. If
defined, aggreg-
ations are cre-
ated as addition-
al tables in the
relational data-
base, thereby in-
creasing its size.
Data is not du-
plicated and pro-
cessing simply
validates SSAS
metadata.
Therefore, data
is available for
querying very
soon after it ar-
rives in the rela-
tional database.
Any MDX queries submitted to
MSAS will be translated into re-
lational SQL queries. ROLAP
performance is generally worse
than that offered by MOLAP. If
you need many aggregations,
the relational database size
could grow exponentially.
Use ROLAP only
if data latency is-
sues cannot be
overcome with
the implementa-
tion of MOLAP
storage.
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