c.h: Add GetDbIdentity, Options::write_dbid_to_manifest (#12736)

Summary:
The write_dbid_to_manifest option is documented as "We recommend setting this flag to true". However, there is no way to set this flag from the C API.

Add the following functions to the C API:

* rocksdb_get_db_identity
* rocksdb_options_get_write_dbid_to_manifest
* rocksdb_options_set_write_dbid_to_manifest

Add a test that this option preserves the ID across checkpoints.

c.cc:
* Remove outdated comments about missing C API functions that exist.
* Document that CopyString is intended for binary data and is not NUL terminated.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/12736

Reviewed By: ltamasi

Differential Revision: D58202117

Pulled By: ajkr

fbshipit-source-id: 707b110df5c4bd118d65548327428a53a9dc3019

3 files changed, 130 insertions, 6 deletions

diff --git a/db/c.cc b/db/c.cc
index 1371e9d0a..3015c8efc 100644
--- a/db/c.cc
+++ b/db/c.cc
@@ -547,6 +547,7 @@ static bool SaveError(char** errptr, const Status& s) {
   return true;
 }
 
+// Copies str to a new malloc()-ed buffer. The buffer is not NUL terminated.
 static char* CopyString(const std::string& str) {
   char* result = reinterpret_cast<char*>(malloc(sizeof(char) * str.size()));
   memcpy(result, str.data(), sizeof(char) * str.size());
@@ -1392,6 +1393,18 @@ char* rocksdb_get_cf_with_ts(rocksdb_t* db,
   return result;
 }
 
+char* rocksdb_get_db_identity(rocksdb_t* db, size_t* id_len) {
+  std::string identity_tmp;
+  Status s = db->rep->GetDbIdentity(identity_tmp);
+  if (!s.ok()) {
+    *id_len = 0;
+    return nullptr;
+  }
+
+  *id_len = identity_tmp.size();
+  return CopyString(identity_tmp);
+}
+
 void rocksdb_multi_get(rocksdb_t* db, const rocksdb_readoptions_t* options,
                        size_t num_keys, const char* const* keys_list,
                        const size_t* keys_list_sizes, char** values_list,
@@ -3946,6 +3959,16 @@ void rocksdb_options_set_plain_table_factory(
   opt->rep.table_factory.reset(factory);
 }
 
+unsigned char rocksdb_options_get_write_dbid_to_manifest(
+    rocksdb_options_t* opt) {
+  return opt->rep.write_dbid_to_manifest;
+}
+
+void rocksdb_options_set_write_dbid_to_manifest(
+    rocksdb_options_t* opt, unsigned char write_dbid_to_manifest) {
+  opt->rep.write_dbid_to_manifest = write_dbid_to_manifest;
+}
+
 void rocksdb_options_set_max_successive_merges(rocksdb_options_t* opt,
                                                size_t v) {
   opt->rep.max_successive_merges = v;
@@ -4325,13 +4348,8 @@ void rocksdb_perfcontext_destroy(rocksdb_perfcontext_t* context) {
 
 /*
 TODO:
-DB::OpenForReadOnly
-DB::KeyMayExist
 DB::GetOptions
 DB::GetSortedWalFiles
-DB::GetLatestSequenceNumber
-DB::GetUpdatesSince
-DB::GetDbIdentity
 DB::RunManualCompaction
 custom cache
 table_properties_collectors
diff --git a/db/c_test.c b/db/c_test.c
index 81291dce5..fd367aeb7 100644
--- a/db/c_test.c
+++ b/db/c_test.c
@@ -798,6 +798,11 @@ int main(int argc, char** argv) {
     rocksdb_delete(db, woptions, "foo", 3, &err);
     CheckNoError(err);
 
+    // get the identity before the backup
+    size_t before_db_id_len = 0;
+    char* before_db_id = rocksdb_get_db_identity(db, &before_db_id_len);
+    CheckCondition(before_db_id_len == 36);
+
     rocksdb_close(db);
 
     rocksdb_destroy_db(options, dbname, &err);
@@ -818,6 +823,14 @@ int main(int argc, char** argv) {
 
     CheckGet(db, roptions, "foo", "hello");
 
+    // the db_identity after the backup is different
+    size_t after_db_id_len = 0;
+    char* after_db_id = rocksdb_get_db_identity(db, &after_db_id_len);
+    CheckCondition(after_db_id_len == 36);
+    CheckCondition(memcmp(after_db_id, before_db_id, after_db_id_len) != 0);
+    Free(&before_db_id);
+    Free(&after_db_id);
+
     rocksdb_backup_engine_close(be);
   }
 
@@ -833,6 +846,14 @@ int main(int argc, char** argv) {
     rocksdb_checkpoint_create(checkpoint, dbcheckpointname, 0, &err);
     CheckNoError(err);
 
+    rocksdb_checkpoint_object_destroy(checkpoint);
+    checkpoint = NULL;
+
+    // get the identity before the checkpoint
+    size_t before_db_id_len = 0;
+    char* before_db_id = rocksdb_get_db_identity(db, &before_db_id_len);
+    CheckCondition(before_db_id_len == 36);
+
     // start a new database from the checkpoint
     rocksdb_close(db);
     rocksdb_options_set_error_if_exists(options, 0);
@@ -841,7 +862,13 @@ int main(int argc, char** argv) {
 
     CheckGet(db, roptions, "foo", "hello");
 
-    rocksdb_checkpoint_object_destroy(checkpoint);
+    // the db_identity after the checkpoint is different
+    size_t after_db_id_len = 0;
+    char* after_db_id = rocksdb_get_db_identity(db, &after_db_id_len);
+    CheckCondition(after_db_id_len == 36);
+    CheckCondition(memcmp(after_db_id, before_db_id, after_db_id_len) != 0);
+    Free(&before_db_id);
+    Free(&after_db_id);
 
     rocksdb_close(db);
     rocksdb_destroy_db(options, dbcheckpointname, &err);
@@ -852,6 +879,73 @@ int main(int argc, char** argv) {
     rocksdb_options_set_error_if_exists(options, 1);
   }
 
+  StartPhase("checkpoint_db_id_in_manifest");
+  {
+    // create new DB with set_write_dbid_to_manifest=true
+    // db_identity is now the same across checkpoints
+    rocksdb_close(db);
+    db = NULL;
+
+    rocksdb_options_t* options_dbid_in_manifest = rocksdb_options_create();
+    rocksdb_options_set_create_if_missing(options_dbid_in_manifest, 1);
+
+    unsigned char write_to_manifest =
+        rocksdb_options_get_write_dbid_to_manifest(options_dbid_in_manifest);
+    CheckCondition(!write_to_manifest);
+    rocksdb_options_set_write_dbid_to_manifest(options_dbid_in_manifest, true);
+    CheckCondition(!write_to_manifest);
+    write_to_manifest =
+        rocksdb_options_get_write_dbid_to_manifest(options_dbid_in_manifest);
+    CheckCondition(write_to_manifest);
+
+    db = rocksdb_open(options_dbid_in_manifest, dbbackupname, &err);
+    CheckNoError(err);
+
+    rocksdb_checkpoint_t* checkpoint =
+        rocksdb_checkpoint_object_create(db, &err);
+    CheckNoError(err);
+
+    rocksdb_checkpoint_create(checkpoint, dbcheckpointname, 0, &err);
+    CheckNoError(err);
+
+    rocksdb_checkpoint_object_destroy(checkpoint);
+    checkpoint = NULL;
+
+    // get the identity before the backup
+    size_t before_db_id_len = 0;
+    char* before_db_id = rocksdb_get_db_identity(db, &before_db_id_len);
+    CheckCondition(before_db_id_len == 36);
+
+    // open the checkpoint
+    rocksdb_close(db);
+    rocksdb_destroy_db(options_dbid_in_manifest, dbbackupname, &err);
+    CheckNoError(err);
+
+    rocksdb_options_set_error_if_exists(options_dbid_in_manifest, 0);
+    db = rocksdb_open(options_dbid_in_manifest, dbcheckpointname, &err);
+    CheckNoError(err);
+
+    // the db_identity after the checkpoint is the same
+    size_t after_db_id_len = 0;
+    char* after_db_id = rocksdb_get_db_identity(db, &after_db_id_len);
+    CheckCondition(after_db_id_len == 36);
+    CheckCondition(memcmp(after_db_id, before_db_id, after_db_id_len) == 0);
+    Free(&before_db_id);
+    Free(&after_db_id);
+
+    rocksdb_close(db);
+    rocksdb_destroy_db(options_dbid_in_manifest, dbcheckpointname, &err);
+    CheckNoError(err);
+    rocksdb_options_destroy(options_dbid_in_manifest);
+    options_dbid_in_manifest = NULL;
+
+    // re-open the default database
+    rocksdb_options_set_error_if_exists(options, 0);
+    db = rocksdb_open(options, dbname, &err);
+    CheckNoError(err);
+    rocksdb_options_set_error_if_exists(options, 1);
+  }
+
   StartPhase("compactall");
   rocksdb_compact_range(db, NULL, 0, NULL, 0);
   CheckGet(db, roptions, "foo", "hello");
diff --git a/include/rocksdb/c.h b/include/rocksdb/c.h
index 89d8a2b18..ed1d871f2 100644
--- a/include/rocksdb/c.h
+++ b/include/rocksdb/c.h
@@ -505,6 +505,13 @@ extern ROCKSDB_LIBRARY_API char* rocksdb_get_cf_with_ts(
     rocksdb_column_family_handle_t* column_family, const char* key,
     size_t keylen, size_t* vallen, char** ts, size_t* tslen, char** errptr);
 
+/**
+ * Returns a malloc() buffer with the DB identity, assigning the length to
+ * *id_len. Returns NULL if an error occurred.
+ */
+extern ROCKSDB_LIBRARY_API char* rocksdb_get_db_identity(rocksdb_t* db,
+                                                         size_t* id_len);
+
 // if values_list[i] == NULL and errs[i] == NULL,
 // then we got status.IsNotFound(), which we will not return.
 // all errors except status status.ok() and status.IsNotFound() are returned.
@@ -1608,6 +1615,11 @@ extern ROCKSDB_LIBRARY_API void rocksdb_options_set_plain_table_factory(
     rocksdb_options_t*, uint32_t, int, double, size_t, size_t, char,
     unsigned char, unsigned char);
 
+extern ROCKSDB_LIBRARY_API unsigned char
+rocksdb_options_get_write_dbid_to_manifest(rocksdb_options_t*);
+extern ROCKSDB_LIBRARY_API void rocksdb_options_set_write_dbid_to_manifest(
+    rocksdb_options_t*, unsigned char);
+
 extern ROCKSDB_LIBRARY_API void rocksdb_options_set_min_level_to_compress(
     rocksdb_options_t* opt, int level);