Database Reference
In-Depth Information
• Each segment is responsible for executing local database operations on its
own set of data. The segments are scanned in parallel.
Note
Once the query is executed, the results are returned to the master, which in turn
returns the results to the client. Optimal distribution and partitioning strategy is
key to the query performance.
Analyzing and optimizing queries
The ANALYZE function
It is very critical to get statistics to realize good query plans that would give good res-
ults. The
ANALYZE
operation requires only a read lock on the table and can possibly
run in parallel.
For
INSERT
,
UPDATE
,
DELETE
, and
CREATE INDEX
operations, always run
ANALYZE
after
running
the
queries.
We
should
use
in
conjunction
with
gp_autostats_on_change_threshold
gp_autostats_mode
to auto analyze during these operations.
Following is the syntax for the
ANALYZE
command:
ANALYZE [table [ (column [, ...] ) ]]
ANALYZE
by default analyzes all tables and all columns unless specified. The stat-
istics for the following scenarios would be useful:
• The
JOIN
condition
• The
WHERE
clause
• The
SORT
clause
• The
GROUP BY
or
HAVING
clause
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