Add ColumnFamilyHandle::GetDescriptor()

Summary:
This patch addes ColumnFamilyHandle::GetDescriptor(), which allows
developers to obtain the CF options and names of the associated column
family given its handle.

  // Returns the up-to-date descriptor used by the current handle.  Since it
  // returns the up-to-date information, this call might internally locks
  // and releases DB mutex to access the up-to-date CF options.
  virtual ColumnFamilyDescriptor GetDescriptor() = 0;

Test Plan: augment column_family_test

Reviewers: sdong, yoshinorim, IslamAbdelRahman, rven, kradhakrishnan, anthony

Reviewed By: anthony

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D51543

db/column_family.cc

@@ -68,6 +68,20 @@ const std::string& ColumnFamilyHandleImpl::GetName() const {
   return cfd()->GetName();
 }
 
+Status ColumnFamilyHandleImpl::GetDescriptor(ColumnFamilyDescriptor* desc) {
+#ifndef ROCKSDB_LITE
+  // accessing mutable cf-options requires db mutex.
+  InstrumentedMutexLock l(mutex_);
+  *desc = ColumnFamilyDescriptor(
+      cfd()->GetName(),
+      BuildColumnFamilyOptions(*cfd()->options(),
+                               *cfd()->GetLatestMutableCFOptions()));
+  return Status::OK();
+#else
+  return Status::NotSupported();
+#endif  // !ROCKSDB_LITE
+}
+
 const Comparator* ColumnFamilyHandleImpl::user_comparator() const {
   return cfd()->user_comparator();
 }

db/column_family.h

@@ -59,6 +59,7 @@ class ColumnFamilyHandleImpl : public ColumnFamilyHandle {
 
   virtual uint32_t GetID() const override;
   virtual const std::string& GetName() const override;
+  virtual Status GetDescriptor(ColumnFamilyDescriptor* desc) override;
 
  private:
   ColumnFamilyData* cfd_;

db/column_family_test.cc

@@ -16,11 +16,12 @@
 #include "rocksdb/db.h"
 #include "rocksdb/env.h"
 #include "rocksdb/iterator.h"
+#include "util/coding.h"
+#include "util/options_parser.h"
 #include "util/string_util.h"
+#include "util/sync_point.h"
 #include "util/testharness.h"
 #include "util/testutil.h"
-#include "util/coding.h"
-#include "util/sync_point.h"
 #include "utilities/merge_operators.h"
 
 namespace rocksdb {
@@ -146,10 +147,18 @@ class ColumnFamilyTest : public testing::Test {
     handles_.resize(cfi + cfs.size());
     names_.resize(cfi + cfs.size());
     for (size_t i = 0; i < cfs.size(); ++i) {
-      ASSERT_OK(db_->CreateColumnFamily(
-          options.size() == 0 ? column_family_options_ : options[i], cfs[i],
-          &handles_[cfi]));
+      const auto& current_cf_opt =
+          options.size() == 0 ? column_family_options_ : options[i];
+      ASSERT_OK(
+          db_->CreateColumnFamily(current_cf_opt, cfs[i], &handles_[cfi]));
       names_[cfi] = cfs[i];
+
+#ifndef ROCKSDB_LITE  // RocksDBLite does not support GetDescriptor
+      // Verify the CF options of the returned CF handle.
+      ColumnFamilyDescriptor desc;
+      ASSERT_OK(handles_[cfi]->GetDescriptor(&desc));
+      RocksDBOptionsParser::VerifyCFOptions(desc.options, current_cf_opt);
+#endif  // !ROCKSDB_LITE
       cfi++;
     }
   }

include/rocksdb/db.h

@@ -50,14 +50,7 @@ class EventListener;
 
 using std::unique_ptr;
 
-class ColumnFamilyHandle {
- public:
-  virtual ~ColumnFamilyHandle() {}
-  virtual const std::string& GetName() const = 0;
-  virtual uint32_t GetID() const = 0;
-};
 extern const std::string kDefaultColumnFamilyName;
-
 struct ColumnFamilyDescriptor {
   std::string name;
   ColumnFamilyOptions options;
@@ -68,6 +61,23 @@ struct ColumnFamilyDescriptor {
       : name(_name), options(_options) {}
 };
 
+class ColumnFamilyHandle {
+ public:
+  virtual ~ColumnFamilyHandle() {}
+  // Returns the name of the column family associated with the current handle.
+  virtual const std::string& GetName() const = 0;
+  // Returns the ID of the column family associated with the current handle.
+  virtual uint32_t GetID() const = 0;
+  // Fills "*desc" with the up-to-date descriptor of the column family
+  // associated with this handle. Since it fills "*desc" with the up-to-date
+  // information, this call might internally lock and release DB mutex to
+  // access the up-to-date CF options.  In addition, all the pointer-typed
+  // options cannot be referenced any longer than the original options exist.
+  //
+  // Note that this function is not supported in RocksDBLite.
+  virtual Status GetDescriptor(ColumnFamilyDescriptor* desc) = 0;
+};
+
 static const int kMajorVersion = __ROCKSDB_MAJOR__;
 static const int kMinorVersion = __ROCKSDB_MINOR__;