Hex encode keys in compaction flush logs (#6616)

Summary:
The raw key bytes are currently dumped directly into the log messages,
which is not ideal if the keys aren't ASCII strings. Null bytes in
particular can cut off bits of the message early.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6616

Reviewed By: ajkr

Differential Revision: D20879218

Pulled By: anand1976

fbshipit-source-id: 825a20715fe6d8012c0163c6e7b8159f7926a1a7

db/db_impl/db_impl_compaction_flush.cc

@@ -2549,8 +2549,8 @@ Status DBImpl::BackgroundCompaction(bool* made_progress,
                        "[%s] Manual compaction from level-%d from %s .. "
                        "%s; nothing to do\n",
                        m->cfd->GetName().c_str(), m->input_level,
-                       (m->begin ? m->begin->DebugString().c_str() : "(begin)"),
-                       (m->end ? m->end->DebugString().c_str() : "(end)"));
+                       (m->begin ? m->begin->DebugString(true).c_str() : "(begin)"),
+                       (m->end ? m->end->DebugString(true).c_str() : "(end)"));
     } else {
       // First check if we have enough room to do the compaction
       bool enough_room = EnoughRoomForCompaction(
@@ -2569,11 +2569,11 @@ Status DBImpl::BackgroundCompaction(bool* made_progress,
             "[%s] Manual compaction from level-%d to level-%d from %s .. "
             "%s; will stop at %s\n",
             m->cfd->GetName().c_str(), m->input_level, c->output_level(),
-            (m->begin ? m->begin->DebugString().c_str() : "(begin)"),
-            (m->end ? m->end->DebugString().c_str() : "(end)"),
+            (m->begin ? m->begin->DebugString(true).c_str() : "(begin)"),
+            (m->end ? m->end->DebugString(true).c_str() : "(end)"),
             ((m->done || m->manual_end == nullptr)
                  ? "(end)"
-                 : m->manual_end->DebugString().c_str()));
+                 : m->manual_end->DebugString(true).c_str()));
       }
     }
   } else if (!is_prepicked && !compaction_queue_.empty()) {