Fix a bug when ingest plaintable sst file (facebook#11969)

Summary:
Plaintable doesn't support SeekToLast. And GetIngestedFileInfo is using SeekToLast without checking the validity.

We are using IngestExternalFile or CreateColumnFamilyWithImport with some sst file in PlainTable format . But after running for a while, compaction error often happens. Such as
![image](https://github.com/facebook/rocksdb/assets/13954644/b4fa49fc-73fc-49ce-96c6-f198a30800b8)

I simply add some std::cerr log to find why.
![image](https://github.com/facebook/rocksdb/assets/13954644/2cf1d5ff-48cc-4125-b917-87090f764fcd)
It shows that the smallest key is always equal to largest key.
![image](https://github.com/facebook/rocksdb/assets/13954644/6d43e978-0be0-4306-aae3-f9e4ae366395)
Then I found the root cause is that PlainTable do not support SeekToLast, so the smallest key is always the same with the largest

I try to write an unit test. But it's not easy to reproduce this error.
(This PR is similar to facebook#11266. Sorry for open another PR)

Pull Request resolved: facebook#11969

Reviewed By: ajkr

Differential Revision: D50933854

Pulled By: cbi42

fbshipit-source-id: 6c6af53c1388922cbabbe64ed3be1cdc58df5431

db/external_sst_file_ingestion_job.cc

@@ -792,8 +792,33 @@ Status ExternalSstFileIngestionJob::GetIngestedFileInfo(
     }
     file_to_ingest->smallest_internal_key.SetFrom(key);
 
-    iter->SeekToLast();
-    pik_status = ParseInternalKey(iter->key(), &key, allow_data_in_errors);
+    Slice largest;
+    if (strcmp(cfd_->ioptions()->table_factory->Name(), "PlainTable") == 0) {
+      // PlainTable iterator does not support SeekToLast().
+      largest = iter->key();
+      for (; iter->Valid(); iter->Next()) {
+        if (cfd_->internal_comparator().Compare(iter->key(), largest) > 0) {
+          largest = iter->key();
+        }
+      }
+      if (!iter->status().ok()) {
+        return iter->status();
+      }
+    } else {
+      iter->SeekToLast();
+      if (!iter->Valid()) {
+        if (iter->status().ok()) {
+          // The file contains at least 1 key since iter is valid after
+          // SeekToFirst().
+          return Status::Corruption("Can not find largest key in sst file");
+        } else {
+          return iter->status();
+        }
+      }
+      largest = iter->key();
+    }
+
+    pik_status = ParseInternalKey(largest, &key, allow_data_in_errors);
     if (!pik_status.ok()) {
       return Status::Corruption("Corrupted key in external file. ",
                                 pik_status.getState());

db/import_column_family_job.cc

@@ -366,8 +366,32 @@ Status ImportColumnFamilyJob::GetIngestedFileInfo(
     bool bound_set = false;
     if (iter->Valid()) {
       file_to_import->smallest_internal_key.DecodeFrom(iter->key());
-      iter->SeekToLast();
-      file_to_import->largest_internal_key.DecodeFrom(iter->key());
+      Slice largest;
+      if (strcmp(cfd_->ioptions()->table_factory->Name(), "PlainTable") == 0) {
+        // PlainTable iterator does not support SeekToLast().
+        largest = iter->key();
+        for (; iter->Valid(); iter->Next()) {
+          if (cfd_->internal_comparator().Compare(iter->key(), largest) > 0) {
+            largest = iter->key();
+          }
+        }
+        if (!iter->status().ok()) {
+          return iter->status();
+        }
+      } else {
+        iter->SeekToLast();
+        if (!iter->Valid()) {
+          if (iter->status().ok()) {
+            // The file contains at least 1 key since iter is valid after
+            // SeekToFirst().
+            return Status::Corruption("Can not find largest key in sst file");
+          } else {
+            return iter->status();
+          }
+        }
+        largest = iter->key();
+      }
+      file_to_import->largest_internal_key.DecodeFrom(largest);
       bound_set = true;
     }