Add a OnManualFlushScheduled callback in event listener (#12631)

Summary:
As titled. Also added the newest user-defined timestamp into the `MemTableInfo`. This can be a useful info in the callback.

Added some unit tests as examples for how users can use two separate approaches to allow manual flush / manual compactions to go through when the user-defined timestamps in memtable only feature is enabled. One approach relies on selectively increase cutoff timestamp in `OnMemtableSeal` callback when it's initiated by a manual flush. Another approach is to increase cutoff timestamp in `OnManualFlushScheduled` callback. The caveats of the approaches are also documented in the unit test.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/12631

Reviewed By: ajkr

Differential Revision: D58260528

Pulled By: jowlyzhang

fbshipit-source-id: bf446d7140affdf124744095e0a179fa6e427532

1 files changed, 21 insertions, 0 deletions

diff --git a/include/rocksdb/listener.h b/include/rocksdb/listener.h
index 452ae54cd..8911bc299 100644
--- a/include/rocksdb/listener.h
+++ b/include/rocksdb/listener.h
@@ -328,6 +328,15 @@ struct BlobFileGarbageInfo : public BlobFileInfo {
   uint64_t garbage_blob_bytes;
 };
 
+struct ManualFlushInfo {
+  // the id of the column family
+  uint32_t cf_id;
+  // the name of the column family
+  std::string cf_name;
+  // Reason that triggered this manual flush
+  FlushReason flush_reason;
+};
+
 struct FlushJobInfo {
   // the id of the column family
   uint32_t cf_id;
@@ -492,6 +501,10 @@ struct MemTableInfo {
   uint64_t num_entries;
   // Total number of deletes in memtable
   uint64_t num_deletes;
+
+  // The newest user-defined timestamps in the memtable. Note this field is
+  // only populated when `persist_user_defined_timestamps` is false.
+  std::string newest_udt;
 };
 
 struct ExternalFileIngestionInfo {
@@ -595,6 +608,14 @@ class EventListener : public Customizable {
   virtual void OnFlushBegin(DB* /*db*/,
                             const FlushJobInfo& /*flush_job_info*/) {}
 
+  // A callback function to RocksDB which will be called after a manual flush
+  // is scheduled. The default implementation is no-op.
+  // The size of the `manual_flush_info` vector should only be bigger than 1 if
+  // the DB enables atomic flush and has more than 1 column families. Its size
+  // should be 1 in all other cases.
+  virtual void OnManualFlushScheduled(
+      DB* /*db*/, const std::vector<ManualFlushInfo>& /*manual_flush_info*/) {}
+
   // A callback function for RocksDB which will be called whenever
   // a SST file is deleted.  Different from OnCompactionCompleted and
   // OnFlushCompleted, this callback is designed for external logging