Thanks for the reply. I carefully followed each step described in the doc. Before the reindex, I closed all the open transactions and management instance. I sent the reindex command from the console and it never returns (at least for 10h+):
mgmt.updateIndex(mgmt.getRelationIndex(flowsTo, "flowsToByTimestamp"), SchemaAction.REINDEX).get()

So I don't have a chance to commit.

But from my monitoring of janusgraph and bigtable, there is no activity after 30min.

Do you have any further suggestion?