Fix blob context when db_iter uses seek (#6051)

Summary:
Fix: when `db_iter` falls back to using seek by `FindValueForCurrentKeyUsingSeek`, `is_blob_` flag is not properly set on encountering BlobIndex.
Also patch existing test for the mentioned code path.
Signed-off-by: tabokie <xy.tao@outlook.com>
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6051

Differential Revision: D18596274

Pulled By: ltamasi

fbshipit-source-id: 8e4714af263b99dc2c379707d50db88fe6799278

HISTORY.md

@@ -21,6 +21,7 @@
 * Fix a assertion failure in MultiGe4t() when BlockBasedTableOptions::no_block_cache is true and there is no compressed block cache
 * If a call to BackupEngine::PurgeOldBackups or BackupEngine::DeleteBackup suffered a crash, power failure, or I/O error, files could be left over from old backups that could only be purged with a call to GarbageCollect. Any call to PurgeOldBackups, DeleteBackup, or GarbageCollect should now suffice to purge such files.
 * Fix a buffer overrun problem in BlockBasedTable::MultiGet() when compression is enabled and no compressed block cache is configured.
+* Fix a bug in DBIter that is_blob_ state isn't updated when iterating backward using seek.
 
 ## 6.5.1 (10/16/2019)
 ### Bug Fixes

db/db_blob_index_test.cc

@@ -398,6 +398,26 @@ TEST_F(DBBlobIndexTest, Iterate) {
     verify(15, Status::kOk, get_value(16, 0), get_value(14, 0),
            create_blob_iterator, check_is_blob(false));
 
+    // Iterator with blob support and using seek.
+    ASSERT_OK(dbfull()->SetOptions(cfh(), {{"max_sequential_skip_in_iterations", "0"}}));
+    verify(1, Status::kOk, get_value(1, 0), get_value(1, 0),
+           create_blob_iterator, check_is_blob(true));
+    verify(3, Status::kOk, get_value(3, 0), get_value(3, 0),
+           create_blob_iterator, check_is_blob(true));
+    verify(5, Status::kOk, get_value(5, 0), get_value(5, 0),
+           create_blob_iterator, check_is_blob(false));
+    verify(7, Status::kOk, get_value(8, 0), get_value(6, 0),
+           create_blob_iterator, check_is_blob(false));
+    verify(9, Status::kOk, get_value(10, 0), get_value(8, 0),
+           create_blob_iterator, check_is_blob(false));
+    verify(11, Status::kNotSupported, "", "", create_blob_iterator);
+    verify(13, Status::kOk,
+           get_value(13, 2) + "," + get_value(13, 1) + "," + get_value(13, 0),
+           get_value(13, 2) + "," + get_value(13, 1) + "," + get_value(13, 0),
+           create_blob_iterator, check_is_blob(false));
+    verify(15, Status::kOk, get_value(16, 0), get_value(14, 0),
+           create_blob_iterator, check_is_blob(false));
+
     for (auto* snapshot : snapshots) {
       dbfull()->ReleaseSnapshot(snapshot);
     }

db/db_iter.cc

@@ -856,6 +856,7 @@ bool DBIter::FindValueForCurrentKeyUsingSeek() {
   // In case read_callback presents, the value we seek to may not be visible.
   // Find the next value that's visible.
   ParsedInternalKey ikey;
+  is_blob_ = false;
   while (true) {
     if (!iter_.Valid()) {
       valid_ = false;
@@ -897,6 +898,7 @@ bool DBIter::FindValueForCurrentKeyUsingSeek() {
   if (ikey.type == kTypeValue || ikey.type == kTypeBlobIndex) {
     assert(iter_.iter()->IsValuePinned());
     pinned_value_ = iter_.value();
+    is_blob_ = (ikey.type == kTypeBlobIndex);
     valid_ = true;
     return true;
   }