Database Reference
In-Depth Information
tables to a large fact table, the optimizer can choose to broadcast the small tables
in their entirety to each S-blade, while keeping the large table distributed
across all snippet processors. This approach minimizes data movement while
taking advantage of the AMPP architecture to parallelize the join.
Snippet Compilation
A compiler converts a query plan into executable code segments, called
snip-
pets
. Query segments are executed by snippet processors in parallel across all
of the data streams in the appliance. Each snippet has two elements: com-
piled code that's executed by individual CPU cores, and a set of FPGA pa-
rameters that customize the embedded engines' filtering for that particular
snippet. This snippet-by-snippet customization enables Netezza to provide,
in effect, a hardware configuration that is optimized on the fly for individual
queries.
The host uses a feature called the
object cache
to further accelerate query
performance. This is a large cache of previously compiled snippet code that
supports parameter variations. For example, a snippet with the clause
WHERE
NAME='Bob'
might use the same compiled code as a snippet with the clause
WHERE NAME='Jim'
but with settings that reflect the different name. This
approach eliminates the compilation step for over 99 percent of snippets.
Just-In-Time Scheduling
The Netezza scheduler balances execution across complex workloads to
meet the objectives of different users, while maintaining maximum utiliza-
tion and throughput. It considers a number of factors, including query prior-
ity, size, and resource availability in determining when to execute snippets
on the S-blades. The appliance architecture enables the scheduler to gather
more up-to-date and accurate metrics about resource availability from each
component of the system. Sophisticated algorithms are at the heart of this
scheduler and empower Netezza to maximize system throughput by utiliz-
ing close to 100 percent of the disk bandwidth while ensuring that memory
and network resources don't get overloaded and cause the system to lose
efficiency. This important characteristic of the Netezza appliance ensures
that the system keeps performing at peak throughput even under very heavy
loads. When the scheduler gives the “green light,” the snippet is broadcast to
all snippet processors throughout the intelligent network fabric.
