LOG more info on oldest snapshot and sequence numbers (#10454)

Summary:
The info LOG file does not currently give any direct
information about the existence of old, live snapshots, nor how to
estimate wall time from a sequence number within the scope of LOG
history. This change addresses both with:
* Logging smallest and largest seqnos for generated SST files, which can
help associate sequence numbers with write time (based on flushes).
* Logging oldest_snapshot_seqno for each compaction, which (along with
that seqno info) helps us to determine how much old data might be kept
around for old (leaked?) snapshots. Including the date here I thought might
be excessive.

I wanted to log the date and seqno of the oldest snapshot with periodic
stats, but the current structure of the code doesn't really support that
because `DumpDBStats` doesn't have access to the DB object.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10454

Test Plan:
manual inspect LOG from
`KEEP_DB=1 ./db_basic_test --gtest_filter=*CompactBetweenSnapshots*`

Reviewed By: ajkr

Differential Revision: D38326948

Pulled By: pdillinger

fbshipit-source-id: 294918ffc04a419844146cd826045321b4d5c038

db/compaction/compaction_job.cc

@@ -1961,7 +1961,10 @@ void CompactionJob::LogCompaction() {
       stream.EndArray();
     }
     stream << "score" << compaction->score() << "input_data_size"
-           << compaction->CalculateTotalInputSize();
+           << compaction->CalculateTotalInputSize() << "oldest_snapshot_seqno"
+           << (existing_snapshots_.empty()
+                   ? int64_t{-1}  // Use -1 for "none"
+                   : static_cast<int64_t>(existing_snapshots_[0]));
   }
 }
 

db/event_helpers.cc

@@ -97,7 +97,8 @@ void EventHelpers::LogAndNotifyTableFileCreationFinished(
             << "file_number" << fd.GetNumber() << "file_size"
             << fd.GetFileSize() << "file_checksum"
             << Slice(file_checksum).ToString(true) << "file_checksum_func_name"
-            << file_checksum_func_name;
+            << file_checksum_func_name << "smallest_seqno" << fd.smallest_seqno
+            << "largest_seqno" << fd.largest_seqno;
 
     // table_properties
     {