Running validation compaction sequentially

Set the snapshot_override option to run validation compaction sequentially rather than in parallel. Switching repair snapshot behavior might be necessary for latency sensitivity reasons.

Set the snapshot_override configuration option to true to run validation compaction sequentially for both subrange and incremental repairs. The repair takes a snapshot of all data on all the nodes and then each node validates the snapshot one at a time.

Switching the repair snapshot behavior might be necessary for latency sensitivity reasons. The snapshot override option determines the manner in which Merkle trees are built during validation compaction: all at once in parallel (default); or one node at a time to reduce impact on server load.

Attention: Be aware that enabling the snapshot override results in considerably slower repair completion times. Roughly estimate the slowdown as equivalent to the replication factor. For instance, with an RF of 3, the repairs builds the Merkle tree three times, one at a time, so sequential compaction could take at least three times as long as parallel.

opscenterd.conf

The location of the opscenterd.conf file depends on the type of installation:

Package installations: /etc/opscenter/opscenterd.conf
Tarball installations: install_location/conf/opscenterd.conf

Procedure

Open opscenterd.conf for editing.
Set the snapshot_override option to True:
```
[repair_service]
snapshot_override=True
```
Restart opscenterd.
Monitor the subrange and incremental repair progress on the Status tab. Be sure to observe the slower progress of validation compactions in the Validation Compactions pane. After differences are determined by Merkle tree comparisons, the streaming progress continues at its regular pace as shown in the Streams pane.