Turn the compression_type check in BlobDBImpl::DecompressSlice into an assertion (#7127)

Summary:
In both cases where `BlobDBImpl::DecompressSlice` is called,
`compression_type` is already checked at the call site; thus, the check
inside the method is redundant and can be turned into an assertion.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7127

Test Plan: `make check`

Reviewed By: zhichao-cao

Differential Revision: D22533454

Pulled By: ltamasi

fbshipit-source-id: ae524443fc6abe0a5fb12327a3fe761a9cd2c831

utilities/blob_db/blob_db_impl.cc

@@ -1148,25 +1148,26 @@ Slice BlobDBImpl::GetCompressedSlice(const Slice& raw,
 Status BlobDBImpl::DecompressSlice(const Slice& compressed_value,
                                    CompressionType compression_type,
                                    PinnableSlice* value_output) const {
-  if (compression_type != kNoCompression) {
-    BlockContents contents;
-    auto cfh = static_cast<ColumnFamilyHandleImpl*>(DefaultColumnFamily());
+  assert(compression_type != kNoCompression);
 
-    {
-      StopWatch decompression_sw(env_, statistics_,
-                                 BLOB_DB_DECOMPRESSION_MICROS);
-      UncompressionContext context(compression_type);
-      UncompressionInfo info(context, UncompressionDict::GetEmptyDict(),
-                             compression_type);
-      Status s = UncompressBlockContentsForCompressionType(
-          info, compressed_value.data(), compressed_value.size(), &contents,
-          kBlockBasedTableVersionFormat, *(cfh->cfd()->ioptions()));
-      if (!s.ok()) {
-        return Status::Corruption("Unable to decompress blob.");
-      }
+  BlockContents contents;
+  auto cfh = static_cast<ColumnFamilyHandleImpl*>(DefaultColumnFamily());
+
+  {
+    StopWatch decompression_sw(env_, statistics_, BLOB_DB_DECOMPRESSION_MICROS);
+    UncompressionContext context(compression_type);
+    UncompressionInfo info(context, UncompressionDict::GetEmptyDict(),
+                           compression_type);
+    Status s = UncompressBlockContentsForCompressionType(
+        info, compressed_value.data(), compressed_value.size(), &contents,
+        kBlockBasedTableVersionFormat, *(cfh->cfd()->ioptions()));
+    if (!s.ok()) {
+      return Status::Corruption("Unable to decompress blob.");
     }
-    value_output->PinSelf(contents.data);
   }
+
+  value_output->PinSelf(contents.data);
+
   return Status::OK();
 }