Seeing indexer activities during doc loading when there is no index created

While investigating AV-73583, I notice that there are indexer activities (ep_dcp_2i_items_sent and ep_dcp_2i_items_remaining) in the background during doc loading phase. Although there are 2 index nodes in the cluster, there is no index created, and there is no query request. Therefore, I don't expect indexer activities while loading docs. I open this ticket to track this issue.

Build: 7.6.0-2149

Job: https://perf.jenkins.couchbase.com/job/CapellaTester2/298/

Support: https://supportal.couchbase.com/snapshot/f00e7baf02a06655e9e9842a50ece7d9::0

Please find details here: https://couchbasecloud.atlassian.net/browse/AV-73583?focusedCommentId=239047

Note that, there is a _system scope and _query collection added in 7.6, and there is a primary index created on the _query collection. According to Kamini, there shouldn’t be indexer activities. 

https://couchbasecloud.atlassian.net/browse/AV-73583?focusedCommentId=239061

The _system scope and _query collection were added in 7.6. That is why you do not see it in 7.2.x

In _query collection, we store:

1.UDF metadata

2.Sequences metadata

3.CBO stats

Since it is not migration and you are still at load- 1 and 2 are obviously not the problem here.

For CBO stats, the stats get collected- when an index finishes building. Since you are not creating indexes yet, CBO stats- shouldn't be generated as well.

The primary index statement issued- should effectively just be a DDL as there are no documents to index in the _query collection yet.

Maybe someone from indexing should take a look as to what is driving the activity on DCP stream.