Update release history to 6.15 (#7673)

Summary:
Update release history to 6.15

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7673

Test Plan: No code change

Reviewed By: ajkr

Differential Revision: D24971069

Pulled By: ramvadiv

fbshipit-source-id: 5cb3f5cbc1b19beb580ea8095acdef72cc092905

HISTORY.md

@@ -1,5 +1,5 @@
 # Rocksdb Change Log
-## Unreleased
+## 6.15.0 (11/13/2020)
 ### Bug Fixes
 * Fixed a bug in the following combination of features: indexes with user keys (`format_version >= 3`), indexes are partitioned (`index_type == kTwoLevelIndexSearch`), and some index partitions are pinned in memory (`BlockBasedTableOptions::pin_l0_filter_and_index_blocks_in_cache`). The bug could cause keys to be truncated when read from the index leading to wrong read results or other unexpected behavior.
 * Fixed a bug when indexes are partitioned (`index_type == kTwoLevelIndexSearch`), some index partitions are pinned in memory (`BlockBasedTableOptions::pin_l0_filter_and_index_blocks_in_cache`), and partitions reads could be mixed between block cache and directly from the file (e.g., with `enable_index_compression == 1` and `mmap_read == 1`, partitions that were stored uncompressed due to poor compression ratio would be read directly from the file via mmap, while partitions that were stored compressed would be read from block cache). The bug could cause index partitions to be mistakenly considered empty during reads leading to wrong read results.

include/rocksdb/version.h

@@ -5,7 +5,7 @@
 #pragma once
 
 #define ROCKSDB_MAJOR 6
-#define ROCKSDB_MINOR 14
+#define ROCKSDB_MINOR 15
 #define ROCKSDB_PATCH 0
 
 // Do not use these. We made the mistake of declaring macros starting with