Tuple mover
The Tuple Mover manages ROS data storage. On mergeout, it combines small ROS containers into larger ones and purges deleted data. The Tuple Mover automatically performs these tasks in the background.
The database mode affects which nodes perform Tuple Mover operations:
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In an Enterprise Mode database, all nodes run the Tuple Mover to perform mergeout operations on the data they store.
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In Eon Mode, the primary subscriber to each shard plans Tuple Mover mergeout operations on the ROS containers in the shard. It can delegate the execution of this plan to another node in the cluster.
Tuple Mover operations typically require no intervention. However, Vertica provides various ways to adjust Tuple Mover behavior. For details, see Managing the tuple mover.
The tuple mover in Eon Mode databases
In Eon Mode, the Tuple Mover's operations are broken into two parts: mergeout planning and mergeout execution. Mergeout planning is always carried out by the primary subscribers of the shards involved in the mergeout. These primary subscribers are part of same the primary subcluster. As part of its mergeout planning, the primary subscriber chooses a node to execute the mergeout plan. It uses two criteria to decide which node should execute the mergeout:
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Only nodes that have memory allocated to their TM resource pool are eligible to perform a mergeout. The primary subscriber ignores all nodes in subclusters whose TM pool's MEMORYSIZE and MAXMEMORYSIZE settings are 0.
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From the group of nodes able to execute a mergeout, the primary subscriber chooses the node that has the most ROS containers in its depot that are involved in the mergeout.
Limiting which subclusters perform mergeout tasks
You can prevent a secondary subcluster from being assigned mergeout tasks by changing the MEMORYSIZE and MAXMEMORYSIZE settings of the its TM pool to 0. These settings prevent the primary subscribers from assigning mergeout tasks to nodes in the subcluster.
Important
Primary subclusters must always be able to execute mergeout tasks. Only change these settings on secondary subclusters.For example, this statement prevents the subcluster named dashboard from running mergeout tasks.
=> ALTER RESOURCE POOL TM FOR SUBCLUSTER dashboard MEMORYSIZE '0%'
MAXMEMORYSIZE '0%';