Bucket compaction

Few questions on compaction behavior (with CB Server 5.1 & 5.5):

1.If we desire to kick off compaction manually, thru couchbase-cli – should the compaction be kicked off on “each node of the cluster” or just once from any node of the cluster?
2. What happens if a compaction op is kicked off, while a previous compaction is still running? Is it safe/non-intrusive OR must we ensure to check if a compaction is currently running before we kick off a new one?
3. If so, how to detect a. if compaction is currently running; b. the progress/stats of the currently running compaction job?

Thanks
AP

@appajee,

It does it for the whole cluster but the process picks a few vbuckets/shards/files per machine until it does them all. Here are the docs on compactions:
https://docs.couchbase.com/server/6.5/manage/manage-settings/configure-compact-settings.html

In the below picture you can see when vbucket/shards/files get compact, even per node , in row 5 , column 3
docs fragmentation. Its just a ratio for row 5, column 1 vs row 5, column 2

Couchbase Is smart enough not to compact files that are currently being compacted.

Unless you have a write heavy use case I would recommend setting compaction to its defaults.