Database Reference
In-Depth Information
The master host is responsible for coordinating the query workload across the seg-
ment hosts. The master does not store user data. Standby master is a warm standby
master. Segment host runs one or more segment instances. Basically, each seg-
ment host runs its own GPDB. Segment hosts run in a
shared nothing
environment
with their own CPU, disk, and memory. Segments store data and are responsible
for executing queries in parallel. The interconnect between the segment hosts is a
high-speed bus or interconnect, pipelining data between the segment hosts. More
on each of the components is explained as follows:
•
Master host
:
• The master host is the entry point to the Greenplum Database sys-
tem. Users connect to the master and interact with the database as
in the case of any other DBMS.
• Internally runs a Postgres listener process (called Postgres) respons-
ible for getting users connected to the database sessions. By default,
this process runs on the port
5432
(daemon process).
• Master host holds all the system and admin utilities used for adminis-
tration tasks.
• Responsible for creating query plans and distributing the workload
across all segment nodes.
• Also responsible for final data aggregations sometimes.
• It holds the metadata and is never responsible for holding the actual
data.
• The master may perform final processing for queries, for example,
aggregations, summations, orders, and sorts. The master does not
contain user data. It is also important to note that system and data-
base administration tasks are performed on the master host. The
parser checks syntax, semantics, and produces a parse tree for the
query optimizer.
The following figure shows master host and its core functions:
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