[SYS-6306] Add sequence number logging to RocksDb-Cloud (#289)

Summary:
Added a thread local boolean that lets us turn on advanced logging to
debug sequence number issues we've been observing.

Test Plan:
Internal testing

Reviewers:

Author: igorcanadi

db/db_impl/db_impl.cc

@@ -6559,4 +6559,10 @@ ColumnFamilyData* DBImpl::GetAnyCFWithAutoFlushDisabled() const {
   return nullptr;
 }
 
+namespace {
+thread_local bool threadLogging{false};
+}
+void SetThreadLogging(bool v) { threadLogging = v; }
+bool GetThreadLogging() { return threadLogging; }
+
 }  // namespace ROCKSDB_NAMESPACE

db/memtable.cc

@@ -974,6 +974,15 @@ static bool SaveValue(void* arg, const char* entry) {
     ValueType type;
     SequenceNumber seq;
     UnPackSequenceAndType(tag, &seq, &type);
+
+    if (GetThreadLogging()) {
+      ROCKS_LOG_INFO(
+          s->logger,
+          "In SaveValue, memtable %p, found key at sequence number: %" PRIu64
+          ", type: %d",
+          s->mem, seq, int(type));
+    }
+
     // If the value is not in the snapshot, skip it
     if (!s->CheckCallback(seq)) {
       return true;  // to continue to the next seq

include/rocksdb/db.h

@@ -1957,4 +1957,7 @@ Status RepairDB(const std::string& dbname, const DBOptions& db_options,
 Status RepairDB(const std::string& dbname, const Options& options);
 #endif
 
+void SetThreadLogging(bool v);
+bool GetThreadLogging();
+
 }  // namespace ROCKSDB_NAMESPACE

table/block_based/block_based_table_reader.cc

@@ -2178,6 +2178,15 @@ Status BlockBasedTable::Get(const ReadOptions& read_options, const Slice& key,
             s = pik_status;
           }
 
+          if (GetThreadLogging()) {
+            ROCKS_LOG_INFO(rep_->ioptions.logger,
+                           "In BlockBasedTable::Get, file %" PRIu64
+                           ", found key at sequence number: %" PRIu64
+                           ", type: %d",
+                           rep_->sst_number_for_tracing(), parsed_key.sequence,
+                           int(parsed_key.type));
+          }
+
           if (!get_context->SaveValue(
                   parsed_key, biter.value(), &matched,
                   biter.IsValuePinned() ? &biter : nullptr)) {