cbq throws error:"msg": "Index scan timed out - cause: Index scan timed out"

1.create a 4 node cluster. I used the ycsb cluster with forestdb indexer storage mode
2. Create index:
CREATE INDEX `idx` ON `default`((meta().`id`)) WITH(

{"index_type" : "forestdb"}

)
3. Issue this query:
cbq> select count(meta().id) from default where meta().id is not null;
{
"requestID": "2aea2242-696f-43ac-8125-c30b83bd919e",
"signature":

{ "$1": "number" }

,
"results": [

{ "$1": 14853475 }

],
"errors": [

{ "code": 12015, "msg": "Index scan timed out - cause: Index scan timed out" }

],
"status": "errors",
"metrics":

{ "elapsedTime": "2m0.361419812s", "executionTime": "2m0.361236106s", "resultCount": 1, "resultSize": 38, "errorCount": 1 }

}

Seems like the backfill issue we saw earlier.

Uploading logs.