Port the batched version of MultiGet() to RocksDB's C API (#9952)

Summary:
The batched version of MultiGet() is not available in RocksDB's C API.
This PR implements rocksdb_batched_multi_get_cf which is a C wrapper function
that invokes the batched version of MultiGet() which takes one single column family.

Pull Request resolved: #9952

Test Plan: Added a new test case under "columnfamilies" test case in c_test.cc

Reviewed By: riversand963

Differential Revision: D36302888

Pulled By: ajkr

fbshipit-source-id: fa134c4a1c8e7d72dd4ae8649a74e3797b5cf4e6

db/c.cc

@@ -1163,6 +1163,43 @@ void rocksdb_multi_get_cf(
   }
 }
 
+void rocksdb_batched_multi_get_cf(rocksdb_t* db,
+                                  const rocksdb_readoptions_t* options,
+                                  rocksdb_column_family_handle_t* column_family,
+                                  size_t num_keys, const char* const* keys_list,
+                                  const size_t* keys_list_sizes,
+                                  rocksdb_pinnableslice_t** values, char** errs,
+                                  const bool sorted_input) {
+  Slice* key_slices = new Slice[num_keys];
+  PinnableSlice* value_slices = new PinnableSlice[num_keys];
+  Status* statuses = new Status[num_keys];
+  for (size_t i = 0; i < num_keys; ++i) {
+    key_slices[i] = Slice(keys_list[i], keys_list_sizes[i]);
+  }
+
+  db->rep->MultiGet(options->rep, column_family->rep, num_keys, key_slices,
+                    value_slices, statuses, sorted_input);
+
+  for (size_t i = 0; i < num_keys; ++i) {
+    if (statuses[i].ok()) {
+      values[i] = new (rocksdb_pinnableslice_t);
+      values[i]->rep = std::move(value_slices[i]);
+      errs[i] = nullptr;
+    } else {
+      values[i] = nullptr;
+      if (!statuses[i].IsNotFound()) {
+        errs[i] = strdup(statuses[i].ToString().c_str());
+      } else {
+        errs[i] = nullptr;
+      }
+    }
+  }
+
+  delete[] key_slices;
+  delete[] value_slices;
+  delete[] statuses;
+}
+
 unsigned char rocksdb_key_may_exist(rocksdb_t* db,
                                     const rocksdb_readoptions_t* options,
                                     const char* key, size_t key_len,

db/c_test.c

@@ -1260,15 +1260,18 @@ int main(int argc, char** argv) {
     rocksdb_writebatch_clear(wb);
     rocksdb_writebatch_put_cf(wb, handles[1], "bar", 3, "b", 1);
     rocksdb_writebatch_put_cf(wb, handles[1], "box", 3, "c", 1);
+    rocksdb_writebatch_put_cf(wb, handles[1], "buff", 4, "rocksdb", 7);
     rocksdb_writebatch_delete_cf(wb, handles[1], "bar", 3);
     rocksdb_write(db, woptions, wb, &err);
     CheckNoError(err);
     CheckGetCF(db, roptions, handles[1], "baz", NULL);
     CheckGetCF(db, roptions, handles[1], "bar", NULL);
     CheckGetCF(db, roptions, handles[1], "box", "c");
+    CheckGetCF(db, roptions, handles[1], "buff", "rocksdb");
     CheckPinGetCF(db, roptions, handles[1], "baz", NULL);
     CheckPinGetCF(db, roptions, handles[1], "bar", NULL);
     CheckPinGetCF(db, roptions, handles[1], "box", "c");
+    CheckPinGetCF(db, roptions, handles[1], "buff", "rocksdb");
     rocksdb_writebatch_destroy(wb);
 
     rocksdb_flush_wal(db, 1, &err);
@@ -1299,6 +1302,26 @@ int main(int argc, char** argv) {
       Free(&vals[i]);
     }
 
+    {
+      const char* batched_keys[4] = {"box", "buff", "barfooxx", "box"};
+      const size_t batched_keys_sizes[4] = {3, 4, 8, 3};
+      const char* expected_value[4] = {"c", "rocksdb", NULL, "c"};
+      char* batched_errs[4];
+
+      rocksdb_pinnableslice_t* pvals[4];
+      rocksdb_batched_multi_get_cf(db, roptions, handles[1], 4, batched_keys,
+                                   batched_keys_sizes, pvals, batched_errs,
+                                   false);
+      const char* val;
+      size_t val_len;
+      for (i = 0; i < 4; ++i) {
+        val = rocksdb_pinnableslice_value(pvals[i], &val_len);
+        CheckNoError(batched_errs[i]);
+        CheckEqual(expected_value[i], val, val_len);
+        rocksdb_pinnableslice_destroy(pvals[i]);
+      }
+    }
+
     {
       unsigned char value_found = 0;
 
@@ -1330,7 +1353,7 @@ int main(int argc, char** argv) {
     for (i = 0; rocksdb_iter_valid(iter) != 0; rocksdb_iter_next(iter)) {
       i++;
     }
-    CheckCondition(i == 3);
+    CheckCondition(i == 4);
     rocksdb_iter_get_error(iter, &err);
     CheckNoError(err);
     rocksdb_iter_destroy(iter);
@@ -1354,7 +1377,7 @@ int main(int argc, char** argv) {
     for (i = 0; rocksdb_iter_valid(iter) != 0; rocksdb_iter_next(iter)) {
       i++;
     }
-    CheckCondition(i == 3);
+    CheckCondition(i == 4);
     rocksdb_iter_get_error(iter, &err);
     CheckNoError(err);
     rocksdb_iter_destroy(iter);

include/rocksdb/c.h

@@ -63,6 +63,7 @@ extern "C" {
 #endif
 
 #include <stdarg.h>
+#include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ -438,6 +439,38 @@ extern ROCKSDB_LIBRARY_API void rocksdb_multi_get_cf(
     const size_t* keys_list_sizes, char** values_list,
     size_t* values_list_sizes, char** errs);
 
+// The MultiGet API that improves performance by batching operations
+// in the read path for greater efficiency. Currently, only the block based
+// table format with full filters are supported. Other table formats such
+// as plain table, block based table with block based filters and
+// partitioned indexes will still work, but will not get any performance
+// benefits.
+//
+// Note that all the keys passed to this API are restricted to a single
+// column family.
+//
+// Parameters -
+// db - the RocksDB instance.
+// options - ReadOptions
+// column_family - ColumnFamilyHandle* that the keys belong to. All the keys
+//                 passed to the API are restricted to a single column family
+// num_keys - Number of keys to lookup
+// keys_list - Pointer to C style array of keys with num_keys elements
+// keys_list_sizes - Pointer to C style array of the size of corresponding key
+//   in key_list with num_keys elements.
+// values - Pointer to C style array of PinnableSlices with num_keys elements
+// statuses - Pointer to C style array of Status with num_keys elements
+// sorted_input - If true, it means the input keys are already sorted by key
+//                order, so the MultiGet() API doesn't have to sort them
+//                again. If false, the keys will be copied and sorted
+//                internally by the API - the input array will not be
+//                modified
+extern ROCKSDB_LIBRARY_API void rocksdb_batched_multi_get_cf(
+    rocksdb_t* db, const rocksdb_readoptions_t* options,
+    rocksdb_column_family_handle_t* column_family, size_t num_keys,
+    const char* const* keys_list, const size_t* keys_list_sizes,
+    rocksdb_pinnableslice_t** values, char** errs, const bool sorted_input);
+
 // The value is only allocated (using malloc) and returned if it is found and
 // value_found isn't NULL. In that case the user is responsible for freeing it.
 extern ROCKSDB_LIBRARY_API unsigned char rocksdb_key_may_exist(