data dictionary

rocksdb作为mysql的一个新的存储引擎，在存储引擎层，会维护自已的元数据信息。在innodb存储引擎中，我们通过information_schema下的INNODB_SYS_DATAFILES，INNODB_SYS_TABLES，INNODB_SYS_INDEXES等表，
可以窥视innodb的元数据信息。同样，rocksdb通过information_schema下的ROCKSDB_INDEX_FILE_MAP，ROCKSDB_DDL，ROCKSDB_GLOBAL_INFO等表可以查看原数据信息。

show create table ROCKSDB_INDEX_FILE_MAP\G

************************* 1. row ***********************

       Table: ROCKSDB_INDEX_FILE_MAP

Create Table: CREATE TEMPORARY TABLE `ROCKSDB_INDEX_FILE_MAP` (

  `COLUMN_FAMILY` int(4) NOT NULL DEFAULT '',

  `INDEX_NUMBER` int(4) NOT NULL DEFAULT '',

  `SST_NAME` varchar(193) NOT NULL DEFAULT '',

  `NUM_ROWS` bigint(8) NOT NULL DEFAULT '',

  `DATA_SIZE` bigint(8) NOT NULL DEFAULT '',

  `ENTRY_DELETES` bigint(8) NOT NULL DEFAULT '',

  `ENTRY_SINGLEDELETES` bigint(8) NOT NULL DEFAULT '',

  `ENTRY_MERGES` bigint(8) NOT NULL DEFAULT '',

  `ENTRY_OTHERS` bigint(8) NOT NULL DEFAULT ''

) ENGINE=MEMORY DEFAULT CHARSET=utf8

show create table ROCKSDB_DDL\G

*********************** 1. row ***********************

       Table: ROCKSDB_DDL

Create Table: CREATE TEMPORARY TABLE `ROCKSDB_DDL` (

  `TABLE_SCHEMA` varchar(193) NOT NULL DEFAULT '',

  `TABLE_NAME` varchar(193) NOT NULL DEFAULT '',

  `PARTITION_NAME` varchar(193) DEFAULT NULL,

  `INDEX_NAME` varchar(193) NOT NULL DEFAULT '',

  `COLUMN_FAMILY` int(4) NOT NULL DEFAULT '',

  `INDEX_NUMBER` int(4) NOT NULL DEFAULT '',

  `INDEX_TYPE` smallint(2) NOT NULL DEFAULT '',

  `KV_FORMAT_VERSION` smallint(2) NOT NULL DEFAULT '',

  `CF` varchar(193) NOT NULL DEFAULT ''

) ENGINE=MEMORY DEFAULT CHARSET=utf8

show create table ROCKSDB_GLOBAL_INFO\G

*********************** 1. row *************************

       Table: ROCKSDB_GLOBAL_INFO

Create Table: CREATE TEMPORARY TABLE `ROCKSDB_GLOBAL_INFO` (

  `TYPE` varchar(513) NOT NULL DEFAULT '',

  `NAME` varchar(513) NOT NULL DEFAULT '',

  `VALUE` varchar(513) NOT NULL DEFAULT ''

) ENGINE=MEMORY DEFAULT CHARSET=utf8

元数据详情

下面我们来具体看看rocksdb维护了哪些元数据信息,从源码中看定义了以下类型，这些数据都以KV的形式存储在名叫__system__的系统column family中。

 // Data dictionary types

  enum DATA_DICT_TYPE {

    DDL_ENTRY_INDEX_START_NUMBER= ,

    INDEX_INFO=                   ,

    CF_DEFINITION=                ,

    BINLOG_INFO_INDEX_NUMBER=     ,

    DDL_DROP_INDEX_ONGOING=       ,

    INDEX_STATISTICS=             ,

    MAX_INDEX_ID=                 ,

    DDL_CREATE_INDEX_ONGOING=     ,

    END_DICT_INDEX_ID=

  };

DDL_ENTRY_INDEX_START_NUMBER
表和索引之间的映射关系
key: Rdb_key_def::DDL_ENTRY_INDEX_START_NUMBER(0x1) + dbname.tablename
value: version + {global_index_id}*n_indexes_of_the_table
INDEX_INFO
索引id和索引属性的关系
key: Rdb_key_def::INDEX_INFO(0x2) + global_index_id
value: version, index_type, key_value_format_version

index_type:主键/二级索引/隐式主键
key_value_format_version: 记录存储格式的版本
CF_DEFINITION
column family属性
key: Rdb_key_def::CF_DEFINITION(0x3) + cf_id
value: version, {is_reverse_cf, is_auto_cf}

is_reverse_cf：是否是reverse column family
is_auto_cf: column family名字是否是$per_index_cf，名字自动由table.indexname组成
BINLOG_INFO_INDEX_NUMBER
binlog位点及gtid信息，binlog_commit更新此信息
key: Rdb_key_def::BINLOG_INFO_INDEX_NUMBER (0x4)
value: version, {binlog_name,binlog_pos,binlog_gtid}
DDL_DROP_INDEX_ONGOING
等待删除的索引信息
key: Rdb_key_def::DDL_DROP_INDEX_ONGOING(0x5) + global_index_id
value: version
INDEX_STATISTICS
索引统计信息
key: Rdb_key_def::INDEX_STATISTICS(0x6) + global_index_id
value: version, {materialized PropertiesCollector::IndexStats}
MAX_INDEX_ID
当前的index id，每次创建索引index id都从这个获取和更新
key: Rdb_key_def::CURRENT_MAX_INDEX_ID(0x7)
value: version, current max index id
DDL_CREATE_INDEX_ONGOING
等待创建的索引信息
key: Rdb_key_def::DDL_CREATE_INDEX_ONGOING(0x8) + global_index_id
value: version

rocksdb DDL 实现

这里以建表和删表来举例

create table
```
CREATE TABLE t1 (a INT, b CHAR(), pk INT AUTO_INCREMENT ,PRIMARY KEY(pk), key idx1(b) comment 'cf_1') ENGINE=rocksdb;
```
通过以下步骤建表
- 创建column family (get_or_create_cf) primary key 存才default column family中，idx1存在cf_1中，需增加一条cf_1的，CF_DEFINITION的记录 {CF_DEFINITION(4)+cf_id(4)} ---> {CF_DEFINITION_VERSION(2)+cf_flags(4)}
- 创建索引两条索引 {INDEX_INFO(4)+cf_id(0)+index_id(260)---> { INDEX_INFO_VERSION_VERIFY_KV_FORMAT(1)+index_type(1)+kv_version(11) {INDEX_INFO(4)+cf_id(2)+index_id(261)---> { INDEX_INFO_VERSION_VERIFY_KV_FORMAT(2)+index_type(2)+kv_version(11)
- 建立表和索引的映射 {DDL_ENTRY_INDEX_START_NUMBER(4)+dbname(test)+tablename(t1) } --> { DDL_ENTRY_INDEX_VERSION+cf_id(0)+index_id(260)+cf_id(2)+index_id(261}
以上信息通过同一batch一起存入rocksdb中。

另外，建索引时，会更新MAX_INDEX_ID信息，使用单独的batch写入，参考(Rdb_seq_generator::get_and_update_next_number)

select * from INFORMATION_SCHEMA.ROCKSDB_DDL where table_name='t1';

+--------------+------------+----------------+------------+---------------+--------------+------------+-------------------+---------+

| TABLE_SCHEMA | TABLE_NAME | PARTITION_NAME | INDEX_NAME | COLUMN_FAMILY | INDEX_NUMBER | INDEX_TYPE | KV_FORMAT_VERSION | CF      |

+--------------+------------+----------------+------------+---------------+--------------+------------+-------------------+---------+

| test         | t1         | NULL           | PRIMARY    |              |           |           |                 | default |

| test         | t1         | NULL           | idx1       |              |           |           |                 | cf_1    |

+--------------+------------+----------------+------------+---------------+--------------+------------+-------------------+---------+

select d.*,i.* from INFORMATION_SCHEMA.ROCKSDB_INDEX_FILE_MAP i,INFORMATION_SCHEMA.ROCKSDB_DDL d where i.INDEX_NUMBER=d.INDEX_NUMBER;

+--------------+------------+----------------+------------+---------------+--------------+------------+-------------------+---------+---------------+--------------+------------+----------+-----------+---------------+---------------------+--------------+--------------+

| TABLE_SCHEMA | TABLE_NAME | PARTITION_NAME | INDEX_NAME | COLUMN_FAMILY | INDEX_NUMBER | INDEX_TYPE | KV_FORMAT_VERSION | CF      | COLUMN_FAMILY | INDEX_NUMBER | SST_NAME   | NUM_ROWS | DATA_SIZE | ENTRY_DELETES | ENTRY_SINGLEDELETES | ENTRY_MERGES | ENTRY_OTHERS |

+--------------+------------+----------------+------------+---------------+--------------+------------+-------------------+---------+---------------+--------------+------------+----------+-----------+---------------+---------------------+--------------+--------------+

| test         | t1         | NULL           | PRIMARY    |              |           |           |                 | default |              |           | .sst |         |         |              |                    |             |             |

| test         | t1         | NULL           | idx1       |              |           |           |                 | cf_1    |              |           | .sst |         |         |              |                    |             |             |

+--------------+------------+----------------+------------+---------------+--------------+------------+-------------------+---------+---------------+--------------+------------+----------+-----------+---------------+---------------------+--------------+--------------+

 rows in set (0.00 sec)

实际数据分布如下图：

元数据分布在系统column family __system__中
primary key 分布在column family default中
idx1 分布在column family cf_1中
黄线之间代表数据分布的范围

drop table

drop table t1;

batch->Put 将索引加入到待删的kv队列中
{DDL_DROP_INDEX_ONGOING(4)+cf_id(0)+index_id(260)} --> {DDL_DROP_INDEX_ONGOING_VERSION(2)}
{DDL_DROP_INDEX_ONGOING(4)+cf_id(2)+index_id(261)} --> {DDL_DROP_INDEX_ONGOING_VERSION(2)}
batch->Delete 删除表的映射关系
表和索引的映射关系

后台线程再从待删的kv队列取出待删的索引，通过 DeleteFilesInRange, CompactRange 删除索引数据。

后台线程确定索引数据删除完成后，batch删除相应的DDL_DROP_INDEX_ONGOING和INDEX_INFO的索引信息。

巴特西

myrocks 之数据字典

data dictionary

元数据详情

rocksdb DDL 实现

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