Summary:
Right now, db_bench with seekrandom and multiple DB setup creates iterator for all DBs just to query one of them. It's different from most real workloads. Fix it by only creating iterators that will be queried.
Also fix a bug that DBs are not destroyed in multi-DB mode.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/7818
Test Plan: Run db_bench with single/multiDB X using/not using tailing iterator with ASAN build, and validate the behavior is expected.
Reviewed By: ajkr
Differential Revision: D25720226
fbshipit-source-id: c2ff7ff7120e5ba64287a30b057c5d29b2cbe20b
1e5b631e51