The recent fix for issue WT-777 works really well. However, I realized that when there are evictions happening, the fast path (the if-statement below) is not triggered and performance sucks.

   if (get_snapshot &&
       txn->id == max_id &&
       txn->snapshot_count == 0 &&
       txn->snap_min == snap_min &&
       TXNID_LE(prev_oldest_id, snap_min)) {
       /* If nothing has changed since last time, we're done. */
       txn_state->snap_min = txn->snap_min;
       if (txn_global->scan_count == 0 &&
           txn_global->oldest_id == prev_oldest_id)
           return;
   }

There are multiple reasons: either get_snapshot is equal to 0 (because of a call __wt_txn_update_oldest from __wt_evict_page) or txn_global->scan_count is not equal to zero.

Michael said: OK, I think this part is easy to fix and I'll push a change shortly. We can avoid incrementing scan count if there is no chance of updating the oldest ID.