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InnoDB adapter

MySQL is the most popular Open Source SQL database management system, is developed, distributed, and supported by Oracle Corporation. InnoDB is a general-purpose storage engine that balances high reliability and high performance in MySQL, since 5.6 InnoDB has become the default MySQL storage engine.

Calcite’s InnoDB adapter allows you to query the data based on InnoDB data files directly as illustrated below, data files are also known as .ibd files. It leverages the innodb-java-reader. This adapter is different from JDBC adapter which maps a schema in a JDBC data source and requires a MySQL server to serve response.

With .ibd files and the corresponding DDLs, the InnoDB adapter acts as a simple “MySQL server”: it accepts SQL queries and attempts to compile each query based on InnoDB file access APIs provided by innodb-java-reader. It projects, filters and sorts directly in the InnoDB data files where possible.

                      SQL query
                       |     |
                      /       \
             ---------         ---------
            |                           |
            v                           v
+-------------------------+  +------------------------+
|      MySQL Server       |  | Calcite InnoDB Adapter |
|                         |  +------------------------+
| +---------------------+ |    +--------------------+
| |InnoDB Storage Engine| |    | innodb-java-reader |
| +---------------------+ |    +--------------------+
+-------------------------+

-------------------- File System --------------------

        +------------+      +-----+
        | .ibd files | ...  |     |    InnoDB Data files
        +------------+      +-----+

What’s more, with DDL statements, the adapter is “index aware”. It leverages rules to choose the appropriate index to scan, for example, using primary key or secondary keys to look up data, then it tries to push down some conditions into storage engine. The adapter also supports hints, so that users can tell the optimizer to use a particular index.

A basic example of a model file is given below, this schema reads from a MySQL “scott” database:

{
  "version": "1.0",
  "defaultSchema": "scott",
  "schemas": [
    {
      "name": "scott",
      "type": "custom",
      "factory": "org.apache.calcite.adapter.innodb.InnodbSchemaFactory",
      "operand": {
        "sqlFilePath": [ "/path/scott.sql" ],
        "ibdDataFileBasePath": "/usr/local/mysql/data/scott"
      }
    }
  ]
}

sqlFilePath is a list of DDL files, you can generate table definitions by executing mysqldump in command-line:

mysqldump -d -u<username> -p<password> -h <hostname> <dbname>

The file content of /path/scott.sql is as follows:

CREATE TABLE `DEPT`(
    `DEPTNO` TINYINT NOT NULL,
    `DNAME` VARCHAR(50) NOT NULL,
    `LOC` VARCHAR(20),
    UNIQUE KEY `DEPT_PK` (`DEPTNO`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

CREATE TABLE `EMP`(
    `EMPNO` INT(11) NOT NULL,
    `ENAME` VARCHAR(100) NOT NULL,
    `JOB` VARCHAR(15) NOT NULL,
    `AGE` SMALLINT,
    `MGR` BIGINT,
    `HIREDATE` DATE,
    `SAL` DECIMAL(8,2) NOT NULL,
    `COMM` DECIMAL(6,2),
    `DEPTNO` TINYINT,
    `EMAIL` VARCHAR(100) DEFAULT NULL,
    `CREATE_DATETIME` DATETIME,
    `CREATE_TIME` TIME,
    `UPSERT_TIME` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
    PRIMARY KEY (`EMPNO`),
    KEY `ENAME_KEY` (`ENAME`),
    KEY `HIREDATE_KEY` (`HIREDATE`),
    KEY `CREATE_DATETIME_JOB_KEY` (`CREATE_DATETIME`, `JOB`),
    KEY `CREATE_TIME_KEY` (`CREATE_TIME`),
    KEY `UPSERT_TIME_KEY` (`UPSERT_TIME`),
    KEY `DEPTNO_JOB_KEY` (`DEPTNO`, `JOB`),
    KEY `DEPTNO_SAL_COMM_KEY` (`DEPTNO`, `SAL`, `COMM`),
    KEY `DEPTNO_MGR_KEY` (`DEPTNO`, `MGR`),
    KEY `AGE_KEY` (`AGE`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

ibdDataFileBasePath is the parent file path of .ibd files.

Assuming the model file is stored as model.json, you can connect to InnoDB data file to perform query via sqlline as follows:

sqlline> !connect jdbc:calcite:model=model.json admin admin

We can query all employees by writing standard SQL:

sqlline> select empno, ename, job, age, mgr from "EMP";
+-------+--------+-----------+-----+------+
| EMPNO | ENAME  |    JOB    | AGE | MGR  |
+-------+--------+-----------+-----+------+
| 7369  | SMITH  | CLERK     | 30  | 7902 |
| 7499  | ALLEN  | SALESMAN  | 24  | 7698 |
| 7521  | WARD   | SALESMAN  | 41  | 7698 |
| 7566  | JONES  | MANAGER   | 28  | 7839 |
| 7654  | MARTIN | SALESMAN  | 27  | 7698 |
| 7698  | BLAKE  | MANAGER   | 38  | 7839 |
| 7782  | CLARK  | MANAGER   | 32  | 7839 |
| 7788  | SCOTT  | ANALYST   | 45  | 7566 |
| 7839  | KING   | PRESIDENT | 22  | null |
| 7844  | TURNER | SALESMAN  | 54  | 7698 |
| 7876  | ADAMS  | CLERK     | 35  | 7788 |
| 7900  | JAMES  | CLERK     | 40  | 7698 |
| 7902  | FORD   | ANALYST   | 28  | 7566 |
| 7934  | MILLER | CLERK     | 32  | 7782 |
+-------+--------+-----------+-----+------+

While executing this query, the InnoDB adapter scans the InnoDB data file EMP.ibd using primary key, also known as clustering B+ tree index in MySQL, and is able to push down projection to underlying storage engine. Projection can reduce the size of data fetched from the storage engine.

We can look up one employee by filtering. The InnoDB adapter retrieves all indexes through DDL file provided in model.json.

sqlline> select empno, ename, job, age, mgr from "EMP" where empno = 7782;
+-------+-------+---------+-----+------+
| EMPNO | ENAME |   JOB   | AGE | MGR  |
+-------+-------+---------+-----+------+
| 7782  | CLARK | MANAGER | 32  | 7839 |
+-------+-------+---------+-----+------+

The InnoDB adapter recognizes that empno is the primary key and performs a point-lookup by using the clustering index instead of a full table scan.

We can also do range queries on the primary key:

sqlline> select empno, ename, job, age, mgr from "EMP" where empno > 7782 and empno < 7900;

Note that such query with acceptable range is usually efficient in MySQL with InnoDB storage engine, because for clustering B+ tree index, records close in index are close in data file, which is good for scanning.

We can look up employee by secondary key. For example, in the following query, the filtering condition is a field ename of type VARCHAR.

sqlline> select empno, ename, job, age, mgr from "EMP" where ename = 'smith';
+-------+-------+-------+-----+------+
| EMPNO | ENAME |  JOB  | AGE | MGR  |
+-------+-------+-------+-----+------+
| 7369  | SMITH | CLERK | 30  | 7902 |
+-------+-------+-------+-----+------+

The InnoDB adapter works well on almost all the commonly used data types in MySQL, for more information on supported data types, please refer to innodb-java-reader.

We can query by composite key. For example, given secondary index of DEPTNO_MGR_KEY.

sqlline> select empno, ename, job, age, mgr from "EMP" where deptno = 20 and mgr = 7566;
+-------+-------+---------+-----+------+
| EMPNO | ENAME |   JOB   | AGE | MGR  |
+-------+-------+---------+-----+------+
| 7788  | SCOTT | ANALYST | 45  | 7566 |
| 7902  | FORD  | ANALYST | 28  | 7566 |
+-------+-------+---------+-----+------+

The InnoDB adapter leverages the matched key DEPTNO_MGR_KEY to push down filtering condition of deptno = 20 and mgr = 7566.

In some cases, only part of the conditions can be pushed down since there is a limitation in the underlying storage engine API; other conditions remain in the rest of the plan. Given the following SQL, only deptno = 20 is pushed down.

select empno, ename, job, age, mgr from "EMP" where deptno = 20 and upsert_time > '2018-01-01 00:00:00';

innodb-java-reader only supports range queries with lower and upper bound using an index, not fully Index Condition Pushdown (ICP). The storage engine returns a range of rows and Calcite evaluates the rest of WHERE condition from the rows fetched.

For the following SQL, there are multiple indexes satisfying the left-prefix index rule: the possible indexes are DEPTNO_JOB_KEY, DEPTNO_SAL_COMM_KEY and DEPTNO_MGR_KEY. The InnoDB adapter chooses one of them according to the ordinal defined in DDL; only the deptno = 20 condition is pushed down, leaving the rest of WHERE condition handled by Calcite’s built-in execution engine.

sqlline> select empno, deptno, sal from "EMP" where deptno = 20 and sal > 2000;
+-------+--------+---------+
| EMPNO | DEPTNO |   SAL   |
+-------+--------+---------+
| 7788  | 20     | 3000.00 |
| 7902  | 20     | 3000.00 |
| 7566  | 20     | 2975.00 |
+-------+--------+---------+

Accessing rows through secondary key requires scanning by secondary index and retrieving records back to clustering index in InnoDB, for a “big” scan, that would introduce many random I/O operations, so performance is usually not good enough. Note that the query above can be more performant by using EPTNO_SAL_COMM_KEY index, because covering index does not need to retrieve back to clustering index. We can force using DEPTNO_SAL_COMM_KEY index by hint as follows.

sqlline> select empno, deptno, sal from "EMP"/*+ index(DEPTNO_SAL_COMM_KEY) */ where deptno = 20 and sal > 2000;

Hint can be configured in SqlToRelConverter, to enable hint, you should register index HintStrategy on TableScan in SqlToRelConverter.ConfigBuilder. Index hint takes effect on the base TableScan relational node, if there are conditions matching the index, index condition can be pushed down as well. For the following SQL, although none of the indexes can be used, but by leveraging covering index, the performance is better than full table scan, we can force to use DEPTNO_MGR_KEY to scan in secondary index.

sqlline> select empno,mgr from "EMP"/*+ index(DEPTNO_MGR_KEY) */ where mgr = 7839;

Ordering can be pushed down if it matches the natural collation of the index used.

sqlline> select deptno,ename,hiredate from "EMP" where hiredate < '2020-01-01' order by hiredate desc;
+--------+--------+------------+
| DEPTNO | ENAME  |  HIREDATE  |
+--------+--------+------------+
| 20     | ADAMS  | 1987-05-23 |
| 20     | SCOTT  | 1987-04-19 |
| 10     | MILLER | 1982-01-23 |
| 20     | FORD   | 1981-12-03 |
| 30     | JAMES  | 1981-12-03 |
| 10     | KING   | 1981-11-17 |
| 30     | MARTIN | 1981-09-28 |
| 30     | TURNER | 1981-09-08 |
| 10     | CLARK  | 1981-06-09 |
| 30     | WARD   | 1981-02-22 |
| 30     | ALLEN  | 1981-02-20 |
| 20     | JONES  | 1981-02-04 |
| 30     | BLAKE  | 1981-01-05 |
| 20     | SMITH  | 1980-12-17 |
+--------+--------+------------+

About time zone

MySQL converts TIMESTAMP values from the current time zone to UTC for storage, and back from UTC to the current time zone for retrieval. So in this adapter, MySQL’s TIMESTAMP is mapped to Calcite’s TIMESTAMP WITH LOCAL TIME ZONE. The per-session time zone setting can be configured in Calcite connection config timeZone, which tells the MySQL server which time zone the TIMESTAMP value was in. Currently the InnoDB adapter cannot pass the property to the underlying storage engine, but you can specify timeZone in model.json like below. Note that you only need to specify the property if timeZone is set in connection config and it is different from system default time zone where the InnoDB adapter runs.

{
  "version": "1.0",
  "defaultSchema": "test",
  "schemas": [
    {
      "name": "test",
      "type": "custom",
      "factory": "org.apache.calcite.adapter.innodb.InnodbSchemaFactory",
      "operand": {
        "sqlFilePath": ["src/test/resources/data_types.sql"],
        "ibdDataFileBasePath": "src/test/resources/data",
        "timeZone": "America/Los_Angeles"
      }
    }
  ]
}

Limitations

innodb-java-reader has some prerequisites for .ibd files.

  • The COMPACT and DYNAMIC row formats are supported. COMPRESSED, REDUNDANT and FIXED are not supported.
  • innodb_file_per_table should set to ON, innodb_file_per_table is enabled by default in MySQL 5.6 and higher.
  • Page size should set to 16K which is also the default value.

For more information, please refer to prerequisites.

In terms of data consistency, you can think of the adapter as a simple MySQL server, with the ability to query directly through InnoDB data file, dump data by offloading from MySQL. If pages are not flushed from InnoDB Buffer Pool to disk, then the result may be inconsistent (the LSN in .ibd file might smaller than in-memory pages). InnoDB leverages write ahead log in terms of performance, so there is no command available to flush all dirty pages. Only internal mechanism manages when and where to persist pages to disk, like Page Cleaner thread, adaptive flushing, etc.

Currently the InnoDB adapter is not aware of row count and cardinality of a .ibd data file, so it relies on simple rules to perform optimization. If, in future, the underlying storage engine can provide such metrics and metadata, this could be integrated into Calcite by leveraging cost based optimization.