Improve result report of scan (#4648)

Summary:
When iterator becomes invalid, there are two possibilities.
First, all data in the column family have been scanned and there is nothing
more to scan.
Second, an underlying error has occurred, causing `status()` to be !ok.
Therefore, we need to check for both cases when `!iter->Valid()`.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4648

Differential Revision: D12959601

Pulled By: riversand963

fbshipit-source-id: 49c9382c9ea9e78f2e2b6f3708f0670b822ca8dd

tools/db_stress.cc

@@ -3600,31 +3600,52 @@ class AtomicFlushStressTest : public StressTest {
     }
     size_t num = column_families_.size();
     assert(num == iters.size());
+    std::vector<Status> statuses(num, Status::OK());
     do {
       size_t valid_cnt = 0;
+      size_t idx = 0;
       for (auto& iter : iters) {
         if (iter->Valid()) {
           ++valid_cnt;
+        } else {
+          statuses[idx] = iter->status();
         }
+        ++idx;
       }
       if (valid_cnt == 0) {
-        break;
-      } else if (valid_cnt != iters.size()) {
-        fprintf(stderr, "Finished iterating the following column families:\n");
+        Status status;
         for (size_t i = 0; i != num; ++i) {
-          if (!iters[i]->Valid()) {
-            fprintf(stderr, "%s ", column_families_[i]->GetName().c_str());
+          const auto& s = statuses[i];
+          if (!s.ok()) {
+            status = s;
+            fprintf(stderr, "Iterator on cf %s has error: %s\n",
+                    column_families_[i]->GetName().c_str(),
+                    s.ToString().c_str());
+            shared->SetVerificationFailure();
           }
         }
-        fprintf(stderr,
-                "\nThe following column families have data that have not been "
-                "scanned:\n");
+        if (status.ok()) {
+          fprintf(stdout, "Finished scanning all column families.\n");
+        }
+        break;
+      } else if (valid_cnt != iters.size()) {
         for (size_t i = 0; i != num; ++i) {
-          if (iters[i]->Valid()) {
-            fprintf(stderr, "%s ", column_families_[i]->GetName().c_str());
+          if (!iters[i]->Valid()) {
+            if (statuses[i].ok()) {
+              fprintf(stderr, "Finished scanning cf %s\n",
+                      column_families_[i]->GetName().c_str());
+            } else {
+              fprintf(stderr, "Iterator on cf %s has error: %s\n",
+                      column_families_[i]->GetName().c_str(),
+                      statuses[i].ToString().c_str());
+            }
+          } else {
+            fprintf(stderr, "cf %s has remaining data to scan\n",
+                    column_families_[i]->GetName().c_str());
           }
         }
-        fprintf(stderr, "\n");
+        shared->SetVerificationFailure();
+        break;
       }
       // If the program reaches here, then all column families' iterators are
       // still valid.