# clickhouse-jdbc-bridge

**Repository Path**: soros_gao/clickhouse-jdbc-bridge

## Basic Information

- **Project Name**: clickhouse-jdbc-bridge
- **Description**: No description available
- **Primary Language**: Unknown
- **License**: Apache-2.0
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2021-12-15
- **Last Updated**: 2021-12-15

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

# ClickHouse JDBC Bridge

![Build](https://github.com/ClickHouse/clickhouse-jdbc-bridge/workflows/Build/badge.svg) ![Release](https://img.shields.io/github/v/release/ClickHouse/clickhouse-jdbc-bridge?include_prereleases)

JDBC bridge for ClickHouse®. It acts as a stateless proxy passing queries from ClickHouse to external datasources. With this extension, you can run distributed query on ClickHouse across multiple datasources in real time, which in a way simplifies the process of building data pipelines for data warehousing, monitoring and integrity check etc.


## Overview

![Overview](https://user-images.githubusercontent.com/4270380/103492828-a06d1200-4e68-11eb-9287-ef830f575d3e.png)


## Known Issues / Limitation

* Connection issue like `jdbc-bridge is not running` or `connect timed out` - see [performance section](#performance) and [this issue](https://github.com/ClickHouse/ClickHouse/issues/9609) for details

* Complex data types like Array and Tuple are currently not supported - they're treated as String

* Pushdown is not supported and query may execute twice because of type inferring

* Mutation is not fully supported - only insertion in simple cases

* Scripting is experimental


## Quick Start

* Docker Compose

    ```bash
    git clone https://github.com/ClickHouse/clickhouse-jdbc-bridge.git
    cd clickhouse-jdbc-bridge/misc/quick-start
    docker-compose up -d
    ...
    docker-compose ps

               Name                         Command               State              Ports
    --------------------------------------------------------------------------------------------------
    quick-start_ch-server_1         /entrypoint.sh                   Up      8123/tcp, 9000/tcp, 9009/tcp
    quick-start_db-mariadb10_1      docker-entrypoint.sh mysqld      Up      3306/tcp
    quick-start_db-mysql5_1         docker-entrypoint.sh mysqld      Up      3306/tcp, 33060/tcp
    quick-start_db-mysql8_1         docker-entrypoint.sh mysqld      Up      3306/tcp, 33060/tcp
    quick-start_db-postgres13_1     docker-entrypoint.sh postgres    Up      5432/tcp
    quick-start_jdbc-bridge_1       /sbin/my_init                    Up      9019/tcp

    # issue below query, and you'll see "ch-server        1" returned
    docker-compose run ch-server clickhouse-client --query="select * from jdbc('self?datasource_column', 'select 1')"
    ```

* Docker CLI

    It's easier to get started using all-in-one docker image:
    ```bash
    # build all-in-one docker image
    git clone https://github.com/ClickHouse/clickhouse-jdbc-bridge.git
    cd clickhouse-jdbc-bridge
    docker build -t my/clickhouse-all-in-one -f all-in-one.Dockerfile .

    # start container in background
    docker run --rm -d --name ch-and-jdbc-bridge my/clickhouse-all-in-one

    # enter container to add datasource and issue query
    docker exec -it ch-and-jdbc-bridge bash

    cp /etc/clickhouse-jdbc-bridge/config/datasources/datasource.json.example \
        /etc/clickhouse-jdbc-bridge/config/datasources/ch-server.json
    
    # you're supposed to see "ch-server        1" returned from ClickHouse
    clickhouse-client --query="select * from jdbc('self?datasource_column', 'select 1')"
    ```

    Alternatively, if you prefer the hard way ;)
    ```bash
    # create a network for ClickHouse and JDBC brigde, so that they can communicate with each other
    docker network create ch-net --attachable
    # start the two containers
    docker run --rm -d --network ch-net --name jdbc-bridge --hostname jdbc-bridge clickhouse/jdbc-bridge
    docker run --rm -d --network ch-net --name ch-server --hostname ch-server \
        --entrypoint /bin/bash yandex/clickhouse-server -c \
        "echo '<yandex><jdbc_bridge><host>jdbc-bridge</host><port>9019</port></jdbc_bridge></yandex>' \
            > /etc/clickhouse-server/config.d/jdbc_bridge_config.xml && /entrypoint.sh"
    # add named datasource and query
    docker exec -it jdbc-bridge cp /app/config/datasources/datasource.json.example \
        /app/config/datasources/ch-server.json
    docker exec -it jdbc-bridge cp /app/config/queries/query.json.example \
        /app/config/queries/show-query-logs.json
    # issue below query, and you'll see "ch-server        1" returned from ClickHouse
    docker exec -it ch-server clickhouse-client \
        --query="select * from jdbc('self?datasource_column', 'select 1')"
    ```

* Debian/RPM Package

    Besides docker, you can download and install released Debian/RPM package on existing Linux system.

    Debian/Ubuntu
    ```bash
    apt update && apt install -y procps wget
    wget https://github.com/ClickHouse/clickhouse-jdbc-bridge/releases/download/v2.0.2/clickhouse-jdbc-bridge_2.0.2-1_all.deb
    apt install --no-install-recommends -f ./clickhouse-jdbc-bridge_2.0.2-1_all.deb
    clickhouse-jdbc-bridge
    ```

    CentOS/RHEL
    ```bash
    yum install -y wget
    wget https://github.com/ClickHouse/clickhouse-jdbc-bridge/releases/download/v2.0.2/clickhouse-jdbc-bridge-2.0.2-1.noarch.rpm
    yum localinstall -y clickhouse-jdbc-bridge-2.0.2-1.noarch.rpm
    clickhouse-jdbc-bridge
    ```

* Java CLI

    ```bash
    wget https://github.com/ClickHouse/clickhouse-jdbc-bridge/releases/download/v2.0.2/clickhouse-jdbc-bridge-2.0.2-shaded.jar
    # add named datasource
    wget -P config/datasources https://raw.githubusercontent.com/ClickHouse/clickhouse-jdbc-bridge/master/misc/quick-start/jdbc-bridge/config/datasources/ch-server.json
    # start jdbc bridge, and then issue below query in ClickHouse for testing
    # select * from jdbc('ch-server', 'select 1')
    java -jar clickhouse-jdbc-bridge-2.0.2-shaded.jar
    ```


## Usage

In most cases, you'll use [jdbc table function](https://clickhouse.tech/docs/en/sql-reference/table-functions/jdbc/) to query against external datasources:
```sql
select * from jdbc('<datasource>', '<schema>', '<query>')
```
`schema` is optional but others are mandatory. Please be aware that the `query` is in native format of the given `datasource`. For example, if the query is `select * from some_table limit 10`, it may work in MariaDB but not in PostgreSQL, as the latter one does not understand `limit`.

Assuming you started a test environment using docker-compose, please refer to examples below to get familiar with JDBC bridge.

* Data Source

    ```sql
    -- show datasources and usage
    select * from jdbc('', 'show datasources')
    -- access named datasource
    select * from jdbc('ch-server', 'select 1')
    -- adhoc datasource is NOT recommended for security reason
    select *
    from jdbc('jdbc:clickhouse://localhost:8123/system?compress=false&ssl=false&user=default', 'select 1')
    ```

* Schema

    By default, any adhoc query passed to JDBC bridge will be executed twice. The first run is for type inferring, while the second for retrieving results. Although metadata will be cached(for up to 5 minutes by default), executing same query twice could be a problem - that's where schema comes into play.
    ```sql
    -- inline schema
    select * from jdbc('ch-server', 'num UInt8, str String', 'select 1 as num, ''2'' as str')
    select * from jdbc('ch-server', 'num Nullable(Decimal(10,0)), Nullable(str FixedString(1)) DEFAULT ''x''', 'select 1 as num, ''2'' as str')
    -- named schema
    select * from jdbc('ch-server', 'query-log', 'show-query-logs')
    ```

* Query
    ```sql
    -- adhoc query
    select * from jdbc('ch-server', 'system', 'select * from query_log where user != ''default''')
    select * from jdbc('ch-server', 'select * from query_log where user != ''default''')
    select * from jdbc('ch-server', 'select * from system.query_log where user != ''default''')

    -- table query
    select * from jdbc('ch-server', 'system', 'query_log')
    select * from jdbc('ch-server', 'query_log')

    -- saved query
    select * from jdbc('ch-server', 'scripts/show-query-logs.sql')

    -- named query
    select * from jdbc('ch-server', 'show-query-logs')

    -- scripting
    select * from jdbc('script', '[1,2,3]')
    select * from jdbc('script', 'js', '[1,2,3]')
    select * from jdbc('script', 'scripts/one-two-three.js')
    ```

* Query Parameters
    ```sql
    select *
    from jdbc('ch-server?datasource_column&max_rows=1&fetch_size=1&one=1&two=2',
        'select {{one}} union all select {{ two }}')
    ```
    Query result:
    ```bash
    ┌─datasource─┬─1─┐
    │ ch-server  │ 1 │
    └────────────┴───┘
    ```

* JDBC Table
    ```sql
    drop table if exists system.test;
    create table system.test (
        a String,
        b UInt8
    ) engine=JDBC('ch-server', '', 'select user as a, is_initial_query as b from system.processes');
    ```

* JDBC Dictionary
    ```sql
    drop dictionary if exists system.dict_test;
    create dictionary system.dict_test
    (
        b UInt64 DEFAULT 0,
        a String
    ) primary key b
    SOURCE(CLICKHOUSE(HOST 'localhost' PORT 9000 USER 'default' TABLE 'test' DB 'system'))
    LIFETIME(MIN 82800 MAX 86400)
    LAYOUT(FLAT());
    ```

* Mutation
    ```sql
    -- use query parameter
    select * from jdbc('ch-server?mutation', 'drop table if exists system.test_table');
    select * from jdbc('ch-server?mutation', 'create table system.test_table(a String, b UInt8) engine=Memory()');
    select * from jdbc('ch-server?mutation', 'insert into system.test_table values(''a'', 1)');
	select * from jdbc('ch-server?mutation', 'truncate table system.test_table');

    -- use JDBC table engine
    drop table if exists system.test_table;
    create table system.test_table (
        a String,
        b UInt8
    ) engine=Memory();

    drop table if exists system.jdbc_table;
    create table system.jdbc_table (
        a String,
        b UInt8
    ) engine=JDBC('ch-server?batch_size=1000', 'system', 'test_table');

    insert into system.jdbc_table(a, b) values('a', 1);

    select * from system.test_table;
    ```
    Query result:
    ```bash
    ┌─a─┬─b─┐
    │ a │ 1 │
    └───┴───┘
    ```

* Monitoring

    You can use [Prometheus](https://prometheus.io/) to monitor metrics exposed by JDBC bridge.
    ```bash
    curl -v http://jdbc-bridge:9019/metrics
    ```


## Configuration

* JDBC Driver

    By default, all JDBC drivers should be placed under `drivers` directory. You can override that by customizing `driverUrls` in datasource configuration file. For example:
    ```json
    {
        "testdb": {
            "driverUrls": [
                "drivers/mariadb",
                "D:\\drivers\\mariadb",
                "/mnt/d/drivers/mariadb",
                "https://repo1.maven.org/maven2/org/mariadb/jdbc/mariadb-java-client/2.7.4/mariadb-java-client-2.7.4.jar"
            ],
            "driverClassName": "org.mariadb.jdbc.Driver",
            ...
        }
    }
    ```

* Named Data Source

    By default, named datasource is defined in configuration file in JSON format under `config/datasources` directory. You may check examples at [misc/quick-start/jdbc-bridge/config/datasources](misc/quick-start/jdbc-bridge/config/datasources). If you use modern editors like VSCode, you may find it's helpful to use [JSON schema](docker/config/datasource.jschema) for validation and smart autocomplete.

* Saved Query

    Saved queries and scripts are under `scripts` directory by default. For example: [show-query-logs.sql](docker/scripts/show-query-logs.sql).

* Named Query

    Similar as named datasource, named queries are JSON configuration files under `config/queries`. You may refer to examples at [misc/quick-start/jdbc-bridge/config/queries](misc/quick-start/jdbc-bridge/config/queries).

* Logging

    You can customize logging configuration in [log4j.properties](docker/log4j.properties).

* Vert.x

    If you're familiar with [Vert.x](https://vertx.io/), you can customize its configuration by changing `config/httpd.json` and `config/vertx.json`.

* Query Parameters

    All supported query parameters can be found at [here](src/main/java/ru/yandex/clickhouse/jdbcbridge/core/QueryParameters.java). `datasource_column=true` can be simplied as `datasource_column`, for example:
    ```sql
    select * from jdbc('ch-server?datasource_column=true', 'select 1')

    select * from jdbc('ch-server?datasource_column', 'select 1')
    ```

* Timeout

    Couple of timeout settings you should be aware of:
    1. datasource timeout, for example: `max_execution_time` in MariaDB
    2. JDBC driver timeout, for example: `connectTimeout` and `socketTimeout` in [MariaDB Connector/J](https://mariadb.com/kb/en/about-mariadb-connector-j/)
    3. JDBC bridge timeout, for examples: `queryTimeout` in `config/server.json`, and `maxWorkerExecuteTime` in `config/vertx.json`
    4. ClickHouse timeout like `max_execution_time` and `keep_alive_timeout` etc.
    5. Client timeout, for example: `socketTimeout` in ClickHouse JDBC driver


## Migration

* Upgrade to 2.x

    2.x is a complete re-write not fully compatible with older version. You'll have to re-define your datasources and update your queries accordingly.


## Build

You can use Maven to build ClickHouse JDBC bridge, for examples:
```bash
git clone https://github.com/ClickHouse/clickhouse-jdbc-bridge.git
cd clickhouse-jdbc-bridge
# compile and run unit tests
mvn -Prelease verify
# release shaded jar, rpm and debian packages
mvn -Prelease package
```

In order to build docker images:
```bash
git clone https://github.com/ClickHouse/clickhouse-jdbc-bridge.git
cd clickhouse-jdbc-bridge
docker build -t my/clickhouse-jdbc-bridge .
# or if you want to build the all-ine-one image
docker build --build-arg revision=20.9.3 -f all-in-one.Dockerfile -t my/clickhouse-all-in-one .
```

## Develop

JDBC bridge is extensible. You may take [ConfigDataSource](src/main/java/ru/yandex/clickhouse/jdbcbridge/impl/ConfigDataSource.java) and [ScriptDataSource](src/main/java/ru/yandex/clickhouse/jdbcbridge/impl/ScriptDataSource.java) as examples to create your own extension.

An extension for JDBC bridge is basically a Java class with 3 optional parts:

1. Extension Name

    By default, extension class name will be treated as name for the extension. However, you can declare a static member in your extension class to override that, for instance:
    ```java
    public static final String EXTENSION_NAME = "myExtension";
    ```

2. Initialize Method

    Initialize method will be called once and only once at the time when loading your extension, for example:
    ```java
    public static void initialize(ExtensionManager manager) {
        ...
    }
    ```

3. Instantiation Method

    In order to create instance of your extension, in general you should define a static method like below so that JDBC bridge knows how(besides walking through all possible constructors):
    ```java
    public static MyExtension newInstance(Object... args) {
        ...
    }
    ```

Assume your extension class is `com.mycompany.MyExtension`, you can load it into JDBC bridge by:

* put your extension package(e.g. my-extension.jar) and required dependencies under `extensions` directory

* update `server.json` by adding your extension, for example
```json
    ...
    "extensions": [
        ...
        {
            "class": "com.mycompany.MyExtension"
        }
    ]
    ...
```
Note: order of the extension matters. The first `NamedDataSource` extension will be set as default for all named datasources.


## Performance

Below is a rough performance comparison to help you understand overhead caused by JDBC bridge as well as its stability. MariaDB, ClickHouse, and JDBC bridge are running on separated KVMs. [ApacheBench(ab)](https://httpd.apache.org/docs/2.4/programs/ab.html) is used on another KVM to simulate 20 concurrent users to issue same query 100,000 times after warm-up. Please refer to [this](misc/perf-test) in order to setup test environment and run tests by yourself.


Test Case | Time Spent(s) | Throughput(#/s) | Failed Requests | Min(ms) | Mean(ms) | Median(ms) | Max(ms)
-- | -- | -- | -- | -- | -- | -- | --
[clickhouse_ping](misc/perf-test/results/clickhouse_ping.txt) | 801.367 | 124.79 | 0 | 1 | 160 | 4 | 1,075
[jdbc-bridge_ping](misc/perf-test/results/jdbc-bridge_ping.txt) | 804.017 | 124.38 | 0 | 1 | 161 | 10 | 3,066
[clickhouse_url(clickhouse)](misc/perf-test/results/clickhouse_url(clickhouse).txt) | 801.448 | 124.77 | 3 | 3 | 160 | 8 | 1,077
[clickhouse_url(jdbc-bridge)](misc/perf-test/results/clickhouse_url(jdbc-bridge).txt) | 811.299 | 123.26 | 446 | 3 | 162 | 10 | 3,066
[clickhouse_constant-query](misc/perf-test/results/clickhouse_constant-query.txt) | 797.775 | 125.35 | 0 | 1 | 159 | 4 | 1,077
[clickhouse_constant-query(mysql)](misc/perf-test/results/clickhouse_constant-query(mysql).txt) | 1,598.426 | 62.56 | 0 | 7 | 320 | 18 | 2,049
[clickhouse_constant-query(remote)](misc/perf-test/results/clickhouse_constant-query(remote).txt) | 802.212 | 124.66 | 0 | 2 | 160 | 8 | 3,073
[clickhouse_constant-query(url)](misc/perf-test/results/clickhouse_constant-query(url).txt) | 801.686 | 124.74 | 0 | 3 | 160 | 11 | 1,123
[clickhouse_constant-query(jdbc)](misc/perf-test/results/clickhouse_constant-query(jdbc).txt) | 925.087 | 108.10 | 5,813 | 14 | 185 | 75 | 4,091
[clickhouse(patched)_constant-query(jdbc)](misc/perf-test/results/clickhouse(patched)_constant-query(jdbc).txt) | 833.892 | 119.92 | 1,577 | 10 | 167 | 51 | 3,109
[clickhouse(patched)_constant-query(jdbc-dual)](misc/perf-test/results/clickhouse(patched)_constant-query(jdbc-dual).txt) | 846.403 | 118.15 | 3,021 | 8 | 169 | 50 | 3,054
[clickhouse_10k-rows-query](misc/perf-test/results/clickhouse_10k-rows-query.txt) | 854.886 | 116.97 | 0 | 12 | 171 | 99 | 1,208
[clickhouse_10k-rows-query(mysql)](misc/perf-test/results/clickhouse_10k-rows-query(mysql).txt) | 1,657.425 | 60.33 | 0 | 28 | 331 | 123 | 2,228
[clickhouse_10k-rows-query(remote)](misc/perf-test/results/clickhouse_10k-rows-query(remote).txt) | 854.610 | 117.01 | 0 | 12 | 171 | 99 | 1,201
[clickhouse_10k-rows-query(url)](misc/perf-test/results/clickhouse_10k-rows-query(url).txt) | 853.292 | 117.19 | 5 | 23 | 171 | 105 | 2,026
[clickhouse_10k-rows-query(jdbc)](misc/perf-test/results/clickhouse_10k-rows-query(jdbc).txt) | 1,483.565 | 67.41 | 11,588 | 66 | 297 | 206 | 2,051
[clickhouse(patched)_10k-rows-query(jdbc)](misc/perf-test/results/clickhouse(patched)_10k-rows-query(jdbc).txt) | 1,186.422 | 84.29 | 6,632 | 61 | 237 | 184 | 2,021
[clickhouse(patched)_10k-rows-query(jdbc-dual)](misc/perf-test/results/clickhouse(patched)_10k-rows-query(jdbc-dual).txt) | 1,080.676 | 92.53 | 4,195 | 65 | 216 | 180 | 2,013

Note: `clickhouse(patched)` is a patched version of ClickHouse server by disabling XDBC bridge health check. `jdbc-dual` on the other hand means dual instances of JDBC bridge managed by docker swarm on same KVM(due to limited resources ;).

Test Case | (Decoded) URL
-- | --
clickhouse_ping | `http://ch-server:8123/ping`
jdbc-bridge_ping | `http://jdbc-bridge:9019/ping`
clickhouse_url(clickhouse) | `http://ch-server:8123/?query=select * from url('http://ch-server:8123/ping', CSV, 'results String')`
clickhouse_url(jdbc-bridge) | `http://ch-server:8123/?query=select * from url('http://jdbc-bridge:9019/ping', CSV, 'results String')`
clickhouse_constant-query | `http://ch-server:8123/?query=select 1`
clickhouse_constant-query(mysql) | `http://ch-server:8123/?query=select * from mysql('mariadb:3306', 'test', 'constant', 'root', 'root')`
clickhouse_constant-query(remote) | `http://ch-server:8123/?query=select * from remote('ch-server:9000', system.constant, 'default', '')`
clickhouse_constant-query(url) | `http://ch-server:8123/?query=select * from url('http://ch-server:8123/?query=select 1', CSV, 'results String')`
clickhouse*_constant-query(jdbc*) | `http://ch-server:8123/?query=select * from jdbc('mariadb', 'constant')`
clickhouse_10k-rows-query | `http://ch-server:8123/?query=select 1`
clickhouse_10k-rows-query(mysql) | `http://ch-server:8123/?query=select * from mysql('mariadb:3306', 'test', '10k_rows', 'root', 'root')`
clickhouse_10k-rows-query(remote) | `http://ch-server:8123/?query=select * from remote('ch-server:9000', system.10k_rows, 'default', '')`
clickhouse_10k-rows-query(url) | `http://ch-server:8123/?query=select * from url('http://ch-server:8123/?query=select * from 10k_rows', CSV, 'results String')`
clickhouse*_10k-rows-query(jdbc*) | `http://ch-server:8123/?query=select * from jdbc('mariadb', 'small-table')`