Allow rocksdb_rate_limiter_bytes_per_sec to be changeable

Summary:
Currently rocksdb_rate_limiter_bytes_per_sec can only be used to set up a rate limiter during
startup.  If the bytes_per_sec value needs to change after startup, that is not possible.  Change this
to allow for this possibility.  If no rate limiter was setup during startup you won't be able to start
and if one is set up during startup you won't be able to disable it.  But if one is set up during startup
the value for the bytes_per_sync will be changeable

Issue mysql#43 (facebook/mysql-5.6#43)

Test Plan: MTR with expanded rocksdb_rate_limiter_bytes_per_sec_basic.test

Reviewers: maykov, yoshinorim, hermanlee4

Reviewed By: hermanlee4

Differential Revision: https://reviews.facebook.net/D48339

Author: jkedgar

storage/rocksdb/ha_rocksdb.cc

@@ -211,11 +211,19 @@ set_compaction_options(THD* thd,
                        void* var_ptr,
                        const void* save);
 
+static void
+set_rate_limiter_bytes_per_sec(THD*                     thd,
+                               struct st_mysql_sys_var* var,
+                               void*                    var_ptr,
+                               const void*              save);
+
 //////////////////////////////////////////////////////////////////////////////
 // Options definitions
 //////////////////////////////////////////////////////////////////////////////
 static long long rocksdb_block_cache_size;
-static uint64_t rocksdb_rate_limiter_bytes_per_sec;
+/* Use unsigned long long instead of uint64_t because of MySQL compatibility */
+static unsigned long long  // NOLINT(runtime/int)
+    rocksdb_rate_limiter_bytes_per_sec;
 static uint64_t rocksdb_info_log_level;
 static char * rocksdb_wal_dir;
 static uint64_t rocksdb_index_type;
@@ -247,6 +255,8 @@ static rocksdb::DBOptions init_db_options() {
 static rocksdb::DBOptions db_options = init_db_options();
 static rocksdb::BlockBasedTableOptions table_options;
 
+static std::shared_ptr<rocksdb::RateLimiter> rate_limiter;
+
 static const char* info_log_level_names[] = {
   "debug_level",
   "info_level",
@@ -316,12 +326,12 @@ static MYSQL_SYSVAR_BOOL(paranoid_checks,
   "DBOptions::paranoid_checks for RocksDB",
   NULL, NULL, db_options.paranoid_checks);
 
-static MYSQL_SYSVAR_ULONG(rate_limiter_bytes_per_sec,
+static MYSQL_SYSVAR_ULONGLONG(rate_limiter_bytes_per_sec,
   rocksdb_rate_limiter_bytes_per_sec,
-  PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_READONLY,
+  PLUGIN_VAR_RQCMDARG,
   "DBOptions::rate_limiter bytes_per_sec for RocksDB",
-  NULL, NULL, 0L,
-  /* min */ 0L, /* max */ LONG_MAX, 0);
+  nullptr, set_rate_limiter_bytes_per_sec, /* default */ 0L,
+  /* min */ 0L, /* max */ ULONGLONG_MAX, 0);
 
 static MYSQL_SYSVAR_ENUM(info_log_level,
   rocksdb_info_log_level,
@@ -1888,8 +1898,9 @@ static int rocksdb_init_func(void *p)
   rocksdb::Status status;
 
   if (rocksdb_rate_limiter_bytes_per_sec != 0) {
-    db_options.rate_limiter.reset(
-      rocksdb::NewGenericRateLimiter(rocksdb_rate_limiter_bytes_per_sec));
+    rate_limiter.reset(rocksdb::NewGenericRateLimiter(
+          rocksdb_rate_limiter_bytes_per_sec));
+    db_options.rate_limiter = rate_limiter;
   }
   db_options.info_log_level = (rocksdb::InfoLogLevel)rocksdb_info_log_level;
   db_options.wal_dir = rocksdb_wal_dir;
@@ -6602,3 +6613,40 @@ set_compaction_options(THD* thd,
     properties_collector_factory->SetCompactionParams(params);
   }
 }
+
+/*
+  This function allows setting the rate limiter's bytes per second value
+  but only if the rate limiter is turned on which has to be done at startup.
+  If the rate is already 0 (turned off) or we are changing it to 0 (trying
+  to turn it off) this function will push a warning to the client and do
+  nothing.
+  This is similar to the code in innodb_doublewrite_update (found in
+  storage/innobase/handler/ha_innodb.cc).
+*/
+void
+set_rate_limiter_bytes_per_sec(THD*                     thd,
+                               struct st_mysql_sys_var* var,
+                               void*                    var_ptr,
+                               const void*              save)
+{
+  uint64_t new_val = *static_cast<const uint64_t*>(save);
+  if (new_val == 0 || rocksdb_rate_limiter_bytes_per_sec == 0)
+  {
+    /*
+      If a rate_limiter was not enabled at startup we can't change it nor
+      can we disable it if one was created at startup
+    */
+    push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN,
+                        ER_WRONG_ARGUMENTS,
+                        "RocksDB: rocksdb_rate_limiter_bytes_per_sec cannot "
+                        "be dynamically changed to or from 0.  Do a clean "
+                        "shutdown if you want to change it from or to 0.");
+  }
+  else if (new_val != rocksdb_rate_limiter_bytes_per_sec)
+  {
+    /* Apply the new value to the rate limiter and store it locally */
+    assert(rate_limiter != nullptr);
+    rocksdb_rate_limiter_bytes_per_sec = new_val;
+    rate_limiter->SetBytesPerSecond(new_val);
+  }
+}