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# 7.3.35. `logical_table_remove`

## 7.3.35.1. Summary

New in version 5.0.5.

`logical_table_remove` removes tables and their columns for the specified logical table. If there are one or more indexes against key of the tables and their columns, they are also removed.

If you specify the part of a shard, table of the shard isn't removed. `logical_table_remove` just deletes records in the table.

For example, there are the following records in a table:

> - Record1: `2016-03-18 00:30:00`
> - Record2: `2016-03-18 01:00:00`
> - Record3: `2016-03-18 02:00:00`

`logical_table_remove` deletes "Record1" and "Record2" when you specify range as between `2016-03-18 00:00:00` and `2016-03-18 01:30:00`. `logical_table_remove` doesn't delete "Record3". `logical_table_remove` doesn't remove the table.

New in version 6.0.1: You can also remove tables and columns that reference the target table and tables related with the target shard by using `dependent` parameter.

## 7.3.35.2. Syntax

This command takes many parameters.

The required parameters are `logical_table` and `shard_key`:

    logical_table_remove logical_table
                         shard_key
                         [min=null]
                         [min_border="include"]
                         [max=null]
                         [max_border="include"]
                         [dependent=no]

## 7.3.35.3. Usage

You specify logical table name and shard key what you want to remove.

This section describes about the followings:

> - Basic usage
> - Removes parts of a logical table
> - Unremovable cases
> - Removes with related tables
> - Decreases used resources

### 7.3.35.3.1. Basic usage

Register `sharding` plugin to use this command in advance.

Execution example:

    register sharding
    # [[0, 1337566253.89858, 0.000355720520019531], true]

You can remove all tables for the logical table by specifying only `logical_table` and `shard_key`.

Here are commands to create 2 shards:

Execution example:

    table_create  Logs_20160318 TABLE_NO_KEY
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_create Logs_20160318 timestamp COLUMN_SCALAR Time
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    table_create  Logs_20160319 TABLE_NO_KEY
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_create Logs_20160319 timestamp COLUMN_SCALAR Time
    # [[0, 1337566253.89858, 0.000355720520019531], true]

You can confirm existing shards by logical_shard_list:

Execution example:

    logical_shard_list --logical_table Logs
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     {
    #       "name": "Logs_20160318"
    #     },
    #     {
    #       "name": "Logs_20160319"
    #     }
    #   ]
    # ]

You can remove all shards:

Execution example:

    logical_table_remove \
      --logical_table Logs \
      --shard_key timestamp
    # [[0, 1337566253.89858, 0.000355720520019531], true]

There are no shards after you remove all shards:

Execution example:

    logical_shard_list --logical_table Logs
    # [[0, 1337566253.89858, 0.000355720520019531], []]

### 7.3.35.3.2. Removes parts of a logical table

You can specify range of shards by the following parameters:

> - `min`
> - `min_border`
> - `max`
> - `max_border`

See the following documents of logical_select for each parameter:

> - min
> - min_border
> - max
> - max_border

If the specified range doesn't cover all records in a shard, table for the shard isn't removed. Target records in the table are only deleted.

If the specified range covers all records in a shard, table for the shard is removed.

Here is a logical table to show the behavior. The logical table has two shards:

Execution example:

    table_create  Logs_20160318 TABLE_NO_KEY
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_create Logs_20160318 timestamp COLUMN_SCALAR Time
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    load --table Logs_20160318
    [
    {"timestamp": "2016-03-18 00:30:00"},
    {"timestamp": "2016-03-18 01:00:00"},
    {"timestamp": "2016-03-18 02:00:00"}
    ]
    # [[0, 1337566253.89858, 0.000355720520019531], 3]
    table_create  Logs_20160319 TABLE_NO_KEY
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_create Logs_20160319 timestamp COLUMN_SCALAR Time
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    load --table Logs_20160319
    [
    {"timestamp": "2016-03-19 00:30:00"},
    {"timestamp": "2016-03-19 01:00:00"}
    ]
    # [[0, 1337566253.89858, 0.000355720520019531], 2]

There are the following records in `Logs_20160318` table:

> - Record1: `"2016-03-18 00:30:00"`
> - Record2: `"2016-03-18 01:00:00"`
> - Record3: `"2016-03-18 02:00:00"`

There are the following records in `Logs_20160319` table:

> - Record1: `"2016-03-19 00:30:00"`
> - Record2: `"2016-03-19 01:00:00"`

The following range doesn't cover "Record1" in `Logs_20160318` table but covers all records in `Logs_20160319` table:

Parameter | Value
--- | ---
`min` | `"2016-03-18 01:00:00"`
`min_border` | `"include"`
`max` | `"2016-03-19 01:30:00"`
`max_border` | `"include"`

`logical_table_remove` with the range deletes "Record2" and "Record3" in `Logs_20160318` table but doesn't remove `Logs_20160318` table. Because there is "Record1" in `Logs_20160318` table.

`logical_table_remove` with the range removes `Logs_20160319` table because the range covers all records in `Logs_20160319` table.

Here is an example to use `logical_table_remove` with the range:

Execution example:

    logical_table_remove \
      --logical_table Logs \
      --shard_key timestamp \
      --min "2016-03-18 01:00:00" \
      --min_border "include" \
      --max "2016-03-19 01:30:00" \
      --max_border "include"
    # [[0, 1337566253.89858, 0.000355720520019531], true]

dump shows that there is "Record1" in `Logs_20160318` table:

Execution example:

    dump
    # plugin_register sharding
    #
    # table_create Logs_20160318 TABLE_NO_KEY
    # column_create Logs_20160318 timestamp COLUMN_SCALAR Time
    #
    # load --table Logs_20160318
    # [
    # ["_id","timestamp"],
    # [1,1458228600.0]
    # ]

### 7.3.35.3.3. Unremovable cases

There are some unremovable cases. See Unremovable cases for details. Because `logical_table_remove` uses the same checks.

### 7.3.35.3.4. Removes with related tables

New in version 6.0.1.

If you understand what you'll do, you can also remove tables and columns that depend on the target shard with one `logical_table_remove` command by using `--dependent yes` parameter.

Here are conditions for dependent. If table or column satisfies one of the conditions, the table or column depends on the target shard:

> - Tables and columns that reference the target shard
> - Tables for the shard (= The table has the same `_YYYYMMDD` postfix as the target shard and is referenced from the target shard)

If there are one or more tables and columns that reference the target shard, `logical_table_remove` is failed. It's for avoiding dangling references.

`Bookmarks.log_20160320` column in the following is the column that references the target shard:

Execution example:

    table_create  Logs_20160320 TABLE_NO_KEY
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_create Logs_20160320 timestamp COLUMN_SCALAR Time
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    table_create Bookmarks TABLE_HASH_KEY ShortText
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_create Bookmarks log_20160320 COLUMN_SCALAR Logs_20160320
    # [[0, 1337566253.89858, 0.000355720520019531], true]

You can't remove `Logs_20160320` by `logical_table_remove` by default:

Execution example:

    logical_table_remove \
      --logical_table Logs \
      --shard_key timestamp
    # [
    #   [
    #     -2,
    #     1337566253.89858,
    #     0.000355720520019531,
    #     "operation not permitted: <[table][remove] a column that references the table exists: <Bookmarks.log_20160320> -> <Logs_20160320",
    #     [
    #       [
    #         "Groonga::Sharding::LogicalTableRemoveCommand.remove_table",
    #         "/home/kou/work/c/groonga.clean/plugins/sharding/logical_table_remove.rb",
    #         80
    #       ]
    #     ]
    #   ]
    # ]

You can remove `Logs_20160320` by `logical_table_remove` with `--dependent yes` parameter. `Bookmarks.log_20160320` is also removed:

Execution example:

    logical_table_remove \
      --logical_table Logs \
      --shard_key timestamp \
      --dependent yes
    # [[0, 1337566253.89858, 0.000355720520019531], true]

object_exist shows that `Logs_20160320` table and `Bookmarks.log_20160320` column are removed:

Execution example:

    object_exist Logs_20160320
    # [[0, 1337566253.89858, 0.000355720520019531], false]
    object_exist Bookmarks.log_20160320
    # [[0, 1337566253.89858, 0.000355720520019531], false]

If there is one or more tables for the target shard, `logical_table_remove` with `--dependent yes` also removes them. Tables that have the same `_YYYYMMDD` postfix as the target shard are treated as tables for the target shard.

Here are two tables that have `_20160320` postfix. `NotRelated_20160320` table isn't used by `Logs_20160320` table. `Users_20160320` table is used by `Logs_20160320` table. `Servers` table exists and used by `Logs_20160320` table:

Execution example:

    table_create  NotRelated_20160320 TABLE_PAT_KEY ShortText
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    table_create  Users_20160320 TABLE_PAT_KEY ShortText
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    table_create  Servers TABLE_PAT_KEY ShortText
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    table_create  Logs_20160320 TABLE_NO_KEY
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_create Logs_20160320 timestamp COLUMN_SCALAR Time
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_create Logs_20160320 user COLUMN_SCALAR Users_20160320
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_create Logs_20160320 server COLUMN_SCALAR Servers
    # [[0, 1337566253.89858, 0.000355720520019531], true]

`logical_table_remove` with `--dependent yes` parameter removes only `Logs_20160320` table and `Users_20160320` table. Because `Users_20160320` table has `_20160320` postfix and used by `Logs_20160320`. `NotRelated_20160320` table and `Servers` table aren't removed. Because `NotRelated_20160320` table has `_20160320` postfix but isn't used by `Logs_20160320`. `Servers` table is used by `Logs_20160320` but doesn't have `_20160320` postfix:

Execution example:

    logical_table_remove \
      --logical_table Logs \
      --shard_key timestamp \
      --dependent yes
    # [[0, 1337566253.89858, 0.000355720520019531], true]

You can confirm that `Logs_20160320` table and `Users_20160320` table are removed but `NotRelated_20160320` table and `Servers` table aren't removed:

Execution example:

    object_exist Logs_20160320
    # [[0, 1337566253.89858, 0.000355720520019531], false]
    object_exist Users_20160320
    # [[0, 1337566253.89858, 0.000355720520019531], false]
    object_exist NotRelated_20160320
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    object_exist Servers
    # [[0, 1337566253.89858, 0.000355720520019531], true]

### 7.3.35.3.5. Decreases used resources

You can decrease resources for this command. See Decreases used resources for details. Because `logical_table_remove` uses the same logic as table_remove.

## 7.3.35.4. Parameters

This section describes parameters of `logical_table_remove`.

### 7.3.35.4.1. Required parameters

There are required parameters.

#### 7.3.35.4.1.1. `logical_table`

Specifies logical table name. It means table name without `_YYYYMMDD` postfix. If you use actual table such as `Logs_20150203`, `Logs_20150203` and so on, logical table name is `Logs`.

See also logical_table.

#### 7.3.35.4.1.2. `shard_key`

Specifies column name which is treated as shared key.

See also shard_key.

### 7.3.35.4.2. Optional parameters

There are optional parameters.

#### 7.3.35.4.2.1. `min`

Specifies the minimum value of `shard_key` column.

See also min.

#### 7.3.35.4.2.2. `min_border`

Specifies whether the minimum value is included or not. `include` and `exclude` are available. The default is `include`.

See also min_border.

#### 7.3.35.4.2.3. `max`

Specifies the maximum value of `shard_key` column.

See also max.

#### 7.3.35.4.2.4. `max_border`

Specifies whether the maximum value is included or not. `include` and `exclude` are available. The default is `include`.

See also max_border.

#### 7.3.35.4.2.5. `dependent`

New in version 6.0.1.

Specifies whether tables and columns that depend on the target shard are also removed or not.

Here are conditions for dependent. If table or column satisfies one of the conditions, the table or column depends on the target shard:

> - Tables and columns that reference the target shard
> - Tables for the shard (= The table has the same `_YYYYMMDD` postfix as the target shard and is referenced from the target shard)

If this value is `yes`, tables and columns that depend on the target shard are also removed. Otherwise, they aren't removed. If there are one or more tables that reference the target shard, an error is returned. If there are tables for the shared, they are not touched.

You should use this parameter carefully. This is a danger parameter.

See Removes with related tables how to use this parameter.

## 7.3.35.5. Return value

The command returns `true` as body on success such as:

    [HEADER, true]

If the command fails, error details are in `HEADER`.

See Output format for `HEADER`.