Add release note for #9747 (#9874)

Summary:
Add release note for CompressedSecondaryCache and the update of SecondaryCache::Lookup().

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9874

Reviewed By: jay-zhuang

Differential Revision: D35765973

Pulled By: gitbw95

fbshipit-source-id: 98232508c4f2047216def9c11a038cfb98709690

HISTORY.md

@@ -23,6 +23,7 @@
 * RocksDB does internal auto prefetching if it notices sequential reads. It starts with readahead size `initial_auto_readahead_size` which now can be configured through BlockBasedTableOptions.
 * Add a merge operator that allows users to register specific aggregation function so that they can does aggregation using different aggregation types for different keys. See comments in include/rocksdb/utilities/agg_merge.h for actual usage. The feature is experimental and the format is subject to change and we won't provide a migration tool.
 * Meta-internal / Experimental: Improve CPU performance by replacing many uses of std::unordered_map with folly::F14FastMap when RocksDB is compiled together with Folly.
+* Experimental: Add CompressedSecondaryCache, a concrete implementation of rocksdb::SecondaryCache, that integrates with compression libraries (e.g. LZ4) to hold compressed blocks.
 
 ### Behavior changes
 * Disallow usage of commit-time-write-batch for write-prepared/write-unprepared transactions if TransactionOptions::use_only_the_last_commit_time_batch_for_recovery is false to prevent two (or more) uncommitted versions of the same key in the database. Otherwise, bottommost compaction may violate the internal key uniqueness invariant of SSTs if the sequence numbers of both internal keys are zeroed out (#9794).
@@ -31,6 +32,7 @@
 ### Public API changes
 * Exposed APIs to examine results of block cache stats collections in a structured way. In particular, users of `GetMapProperty()` with property `kBlockCacheEntryStats` can now use the functions in `BlockCacheEntryStatsMapKeys` to find stats in the map.
 * Add `fail_if_not_bottommost_level` to IngestExternalFileOptions so that ingestion will fail if the file(s) cannot be ingested to the bottommost level.
+* Add output parameter `is_in_sec_cache` to `SecondaryCache::Lookup()`. It is to indicate whether the handle is possibly erased from the secondary cache after the Lookup.
 
 ## 7.1.0 (03/23/2022)
 ### New Features