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# 7.22. Sharding

Added in version 5.0.0.

Groonga has Limitations against table size. You can’t add 268,435,455 more records in one table.

Groonga supports time based sharding to resolve the limitation.

It works in the same database. It doesn’t work with multiple databases. It means that this sharding feature isn’t for distributing large data to multiple hosts.

If you want distributed sharding feature, use Mroonga or PGroonga. You can use sharding feature by MySQL or PostgreSQL. You’ll be able to use Droonga for distributed sharding feature soon.

## 7.22.1. Summary

Sharding is implemented in `sharding` plugin. The plugin is written in mruby. You need to enable mruby when you build Groonga.

You can confirm whether your Groonga supports mruby or not by `--version` command line argument of groonga executable file:

    % groonga --version
    groonga 5.0.5 [...,mruby,...]

    configure options: <...>

If you find `mruby`, your Groonga supports mruby.

`sharding` plugin provides only search commands. They have `logical_` prefix in their command names such as logical_select and logical_range_filter.

`sharding` plugin doesn’t provide schema define commands and data load commands yet. You need to use existing commands such as table_create, column_create and load.

`sharding` plugin requires some rules against table and column. You need to follow these rules. They are described later.

## 7.22.2. Glossary

Name | Description
--- | ---
Logical table | It’s a table that consists of shards. It doesn’t exist in Groonga database. It just exists in our minds.
Logical table name | The name of logical table. It’s prefix of shard names. For example, `Logs` is a logical table name and `Logs_20150814` and `Logs_20150815` are shard names.
Shard | It’s a table that has records in a day or month. One shard has only partial records. Shard name (= table name) must follow `${LOGICAL_TABLE_NAME}_${YYYYMMDD}` format or `${LOGICAL_TABLE_NAME}_${YYYYMM}` format. `${LOGICAL_TABLE_NAME}` is expanded to logical table name. `${YYYYMMDD}` is expanded to day. `${YYYYMM}` is expanded to month. For example, `Logs_20150814` is consists of `Logs` logical name and `20150814` day.

## 7.22.3. Rules

TODO

## 7.22.4. Commands

- logical_count

- logical_parameters

- logical_range_filter

- logical_select

- logical_shard_list

- logical_table_remove