Github user iilyak commented on the pull request:
https://github.com/apache/couchdb-couch-index/pull/16#issuecomment-219868691
@rnewson: This change is for view_compaction (not db compaction). Here is
my understanding of how it would work.
- The entry point to trigger compaction is
[`couch_index:compact`](https://github.com/cloudant/couchdb-couch-index/blob/a3af68f86ee21a9e072507b9d1d7da11e001b299/src/couch_index.erl#L76).
- It will do [gen_server:call(CPid,
compact)](https://github.com/apache/couchdb-couch-index/blob/master/src/couch_index.erl#L77)
to compactor Pid.
- `couch_index_compactor` would [spawn_link(fun() ->
compact/3..](https://github.com/apache/couchdb-couch-index/blob/master/src/couch_index_compactor.erl#L64).
- `couch_index_compactor:compact/3` would call
[Mod:compact/3](https://github.com/apache/couchdb-couch-index/blob/master/src/couch_index_compactor.erl#L104).
In our case `Mod` would be `couch_mrview_index`.
- `couch_mrview_index:compact/3` would dispatch the call to
[couch_mrview_compactor:compact/3](https://github.com/apache/couchdb-couch-mrview/blob/master/src/couch_mrview_index.erl#L193).
- When compaction is finished we get control back into
[couch_index_compactor:compact](https://github.com/apache/couchdb-couch-index/blob/master/src/couch_index_compactor.erl#L106).
- Where right after `couch_mrview_compactor` we do
`Mod:commit(NewIdxState)`. We notify couch_index by doing [gen_server:call(Idx,
{compacted,
NewIdxState})](https://github.com/apache/couchdb-couch-index/blob/master/src/couch_index_compactor.erl#L107).
- I.e. we get
[here](https://github.com/cloudant/couchdb-couch-index/blob/a3af68f86ee21a9e072507b9d1d7da11e001b299/src/couch_index.erl#L191).
Where we can check if re-compaction is enabled.
- If re-compaction is not enabled we swap files.
Otherwise we reply `{reply, recompact, State}`. So we can trigger
[couch_mrview_index:compact(_, _,
[recompact])](https://github.com/cloudant/couchdb-couch-index/blob/a3af68f86ee21a9e072507b9d1d7da11e001b299/src/couch_index_compactor.erl#L108:L110).
Please let me know what I'm missing.
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