Redistribute tables to balance existing data over the newly expanded cluster.
After creating an expansion schema, you can redistribute tables across the entire system with gpexpand. Plan to run this during low-use hours when the utility’s CPU usage and table locks have minimal impact on operations. Rank tables to redistribute the largest or most critical tables first.
Note: When redistributing data, Greenplum Database must be running in production mode. Greenplum Database cannot be in restricted mode or in master mode. The gpstart options
-m cannot be specified to start Greenplum Database.
While table redistribution is underway, any new tables or partitions created are distributed across all segments exactly as they would be under normal operating conditions. Queries can access all segments, even before the relevant data is redistributed to tables on the new segments. The table or partition being redistributed is locked and unavailable for read or write operations. When its redistribution completes, normal operations resume.
- Ranking Tables for Redistribution
- Redistributing Tables Using gpexpand
- Monitoring Table Redistribution
Parent topic:Expanding a Greenplum System
For large systems, you can control the table redistribution order. Adjust tables’
rank values in the expansion schema to prioritize heavily-used tables and minimize performance impact. Available free disk space can affect table ranking; see Managing Redistribution in Large-Scale Greenplum Systems.
To rank tables for redistribution by updating
rank values in gpexpand.status_detail, connect to Greenplum Database using
psql or another supported client. Update gpexpand.status_detail with commands such as:
=> UPDATE gpexpand.status_detail SET rank=10; => UPDATE gpexpand.status_detail SET rank=1 WHERE fq_name = 'public.lineitem'; => UPDATE gpexpand.status_detail SET rank=2 WHERE fq_name = 'public.orders';
These commands lower the priority of all tables to
10 and then assign a rank of
lineitem and a rank of
orders. When table redistribution begins,
lineitem is redistributed first, followed by
orders and all other tables in gpexpand.status_detail. To exclude a table from redistribution, remove the table from the gpexpand.status_detail table.
- Log in on the master host as the user who will run your Greenplum Database system, for example,
gpexpandutility. You can use the
-eoption to define the expansion session time period. For example, to run the utility for up to 60 consecutive hours:
$ gpexpand -d 60:00:00
The utility redistributes tables until the last table in the schema completes or it reaches the specified duration or end time.
gpexpandupdates the status and time in gpexpand.status when a session starts and finishes.
Note: After completing table redistribution, run the
VACUUM ANALYZE and
REINDEXcommands on the catalog tables to update table statistics, and rebuild indexes. See Routine Vacuum and Analyze in the Administration Guide and
VACUUM in the Reference Guide.
During the table redistribution process you can query the expansion schema to view:
- a current progress summary, the estimated rate of table redistribution, and the estimated time to completion. Use gpexpand.expansion_progress, as described in Viewing Expansion Status.
- per-table status information, using gpexpand.status_detail. See Viewing Table Status.
See also Monitoring the Cluster Expansion State for information about monitoring the overall expansion progress with the
After the first table completes redistribution, gpexpand.expansion_progress calculates its estimates and refreshes them based on all tables’ redistribution rates. Calculations restart each time you start a table redistribution session with
gpexpand. To monitor progress, connect to Greenplum Database using
psql or another supported client; query gpexpand.expansion_progress with a command like the following:
=# SELECT * FROM gpexpand.expansion_progress; name | value ------------------------------+----------------------- Bytes Left | 5534842880 Bytes Done | 142475264 Estimated Expansion Rate | 680.75667095996092 MB/s Estimated Time to Completion | 00:01:01.008047 Tables Expanded | 4 Tables Left | 4 (6 rows)
The table gpexpand.status_detail stores status, time of last update, and more facts about each table in the schema. To see a table’s status, connect to Greenplum Database using
psql or another supported client and query gpexpand.status_detail:
=> SELECT status, expansion_started, source_bytes FROM gpexpand.status_detail WHERE fq_name = 'public.sales'; status | expansion_started | source_bytes -----------+----------------------------+-------------- COMPLETED | 2017-02-20 10:54:10.043869 | 4929748992 (1 row)