# 7.3.24. `io_flush`

## 7.3.24.1. Summary

New in version 5.0.5.

`io_flush` flushes all changes in memory to disk explicitly. Normally, you don’t need to use `io_flush` explicitly. Because flushing is done automatically by OS. And flushing by OS is effective.

You need to use `io_flush` explicitly when your system may often crash unexpectedly or you may not shutdown your Groonga process in a normal way. (For example, using shutdown is a normal shutdown process.) It’s better that you use `io_flush` after you change your Groonga database for the case. Here are commands that change your Groonga database:

> - column_create

> - column_remove

> - column_rename

> - delete

> - load

> - logical_table_remove

> - object_remove

> - plugin_register

> - plugin_unregister

> - table_create

> - table_remove

> - table_rename

> - truncate

If you’re using scorer parameter in select to change existing column values, select is added to the above list.

Note that `io_flush` may be a heavy process. If there are many changes in memory, flushing them to disk is a heavy process.

New in version 8.0.8: `io_flush` locks Groonga database while flushing. It means that you can’t run the following commands while `io_flush`:

> - column_create

> - column_remove

> - column_rename

> - logical_table_remove

> - object_remove

> - plugin_register

> - plugin_unregister

> - table_create

> - table_remove

> - table_rename

## 7.3.24.2. Syntax

This command takes three parameters.

All parameters are optional:

    io_flush [target_name=null]
             [recursive=yes]
             [only_opened=no]

New in version 7.0.4: only_opened is added.

New in version 9.0.2: `--recursive dependent` option is added. It is recommended way to flush target object and its related objects since 9.0.2. See recursive about details.

## 7.3.24.3. Usage

You can flush all changes in memory to disk with no arguments:

Execution example:

    io_flush
    # [[0, 1337566253.89858, 0.000355720520019531], true]

If you know what is changed, you can narrow flush targets. Here is a correspondence table between command and flush targets for Groonga 9.0.2 or later.

Note

There is a different recommended way which depends on Groonga version. If Groonga is 9.0.1 or earlier ( `--recursive dependent` is not available ), you need to flush related objects explicitly, otherwise, using `--recursive dependent` is a recommended way not to forget flush target objects.

Command | Flush targets | `io_flush` arguments
--- | --- | ---
load and delete | Target table and its columns. If there are one or more reference columns in these columns, referenced tables are also flush targets. If there are one or more indexed columns in these columns, tables of corresponding index columns and corresponding index columns are also flush targets. | Use `--recursive dependent` to flush target table and its columns, referenced tables and tables of corresponding index columns and corresponding index columns at once:
    io_flush --target_name TABLE_NAME --recursive dependent
truncate | Target table and its columns. If there are one or more reference columns in these columns, referenced tables are also flush targets. If there are one or more indexed columns in these columns, tables of corresponding index columns and corresponding index columns are also flush targets. Database is also flush target. | Use `--recursive dependent` to flush target table and its columns, referenced tables and tables of corresponding index columns and corresponding index columns at once:
    io_flush --target_name TABLE_NAME --recursive dependent
table_create | Target table and database. | Table:
    io_flush --target_name TABLE_NAME --recursive dependent
table_remove, table_rename and logical_table_remove | Database. | Database:
    io_flush --recursive no
column_create | Target column and database. | Table:
    io_flush --target_name TABLE_NAME.COLUMN_NAME --recursive dependent
column_remove and column_rename | Database. | Database:
    io_flush --recursive no
plugin_register and plugin_unregister | Database. | Database:
    io_flush --recursive no

If Groonga is 9.0.1 or earlier ( `--recursive dependent` is not available ), flush objects explicitly. Here is a correspondence table between command and flush targets for Groonga 9.0.1 or earlier.

Command | Flush targets | `io_flush` arguments
--- | --- | ---
load and delete | Target table and its columns. If there are one or more reference columns in these columns, referenced tables are also flush targets. If there are one or more indexed columns in these columns, tables of corresponding index columns and corresponding index columns are also flush targets. | Table and its columns:
    io_flush --target_name TABLE_NAME
A referenced table:
    io_flush --target_name REFERENCED_TABLE_NAME --recursive no
A table of an index column:
    io_flush --target_name TABLE_NAME_OF_INDEX_COLUMN --recursive no
An index column:
    io_flush --target_name TABLE_NAME_OF_INDEX_COLUMN.INDEX_COLUMN
truncate | Target table and its columns. If there are one or more reference columns in these columns, referenced tables are also flush targets. If there are one or more indexed columns in these columns, tables of corresponding index columns and corresponding index columns are also flush targets. Database is also flush target. | Table and its columns:
    io_flush --target_name TABLE_NAME
A referenced table:
    io_flush --target_name REFERENCED_TABLE_NAME --recursive no
A table of an index column:
    io_flush --target_name TABLE_NAME_OF_INDEX_COLUMN --recursive no
An index column:
    io_flush --target_name TABLE_NAME_OF_INDEX_COLUMN.INDEX_COLUMN
Database:
    io_flush --recursive no
table_create | Target table and database. | Table:
    io_flush --target_name TABLE_NAME
Database:
    io_flush --recursive no
table_remove, table_rename and logical_table_remove | Database. | Database:
    io_flush --recursive no
column_create | Target column and database. | Table:
    io_flush --target_name TABLE_NAME.COLUMN_NAME
Database:
    io_flush --recursive no
column_remove and column_rename | Database. | Database:
    io_flush --recursive no
plugin_register and plugin_unregister | Database. | Database:
    io_flush --recursive no

## 7.3.24.4. Parameters

This section describes all parameters.

### 7.3.24.4.1. Required parameters

There is no required parameter.

### 7.3.24.4.2. Optional parameters

There are optional parameters.

#### 7.3.24.4.2.1. `target_name`

Specifies a target object name. Target object is one of database, table or column.

If you omit this parameter, database is the target object:

Execution example:

    io_flush
    # [[0, 1337566253.89858, 0.000355720520019531], true]

If you specify a table name, the table is the target object:

Execution example:

    table_create Users TABLE_HASH_KEY ShortText
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    io_flush --target_name Users
    # [[0, 1337566253.89858, 0.000355720520019531], true]

If you specify a column name, the column is the target object:

Execution example:

    column_create Users age COLUMN_SCALAR UInt8
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    io_flush --target_name Users.age
    # [[0, 1337566253.89858, 0.000355720520019531], true]

#### 7.3.24.4.2.2. `recursive`

Specifies whether child objects of the target object are also target objects.

Child objects of database are all tables and all columns.

Child objects of table are all its columns.

Child objects of column are nothing.

If you specify `yes` to only_opened, `recursive` is ignored.

`recursive` value must be `yes`, `no` or `dependent`. `yes` means that all of the specified target object and child objects are the target objects. `no` means that only the specified target object is the target object. `dependent` means that all of the specified target object, child objects, corresponding table of index column and corresponding index column are the target objects.

The following `io_flush` flushes all changes in database, all tables and all columns:

Execution example:

    io_flush --recursive yes
    # [[0, 1337566253.89858, 0.000355720520019531], true]

The following `io_flush` flushes all changes only in database:

Execution example:

    io_flush --recursive no
    # [[0, 1337566253.89858, 0.000355720520019531], true]

If you specify other value (not `yes` neither `no`) or omit `recursive` parameter, `yes` is used.

`yes` is used in the following case because invalid `recursive` argument is specified:

Execution example:

    io_flush --recursive invalid
    # [[0, 1337566253.89858, 0.000355720520019531], true]

`yes` is used in the following case because `recursive` parameter isn’t specified:

Execution example:

    io_flush
    # [[0, 1337566253.89858, 0.000355720520019531], true]

Since 9.0.2, `--recursive dependent` is added to flush not only target object and child objects, but also related objects. The related objects are:

- A referenced table

- A related index column (There is source column in target `TABLE_NAME`)

- A table of related index column (There is source column in target `TABLE_NAME`)

It is useful not to forget flushing related objects.

For example, `--recursive dependent` is specified for `TABLE_NAME`, this option executes equivalent to the following commands internally.

- Flush table and its columns:

      io_flush --target_name TABLE_NAME --recursive yes

- Flush a referenced table:

      io_flush --target_name REFERENCED_TABLE_NAME --recursive no

- Flush a related index column (There is source column in `TABLE_NAME`):

      io_flush --target_name TABLE_NAME_OF_INDEX_COLUMN.INDEX_COLUMN

- Flush a table of related index column (There is source column in `TABLE_NAME`):

      io_flush --target_name TABLE_NAME_OF_INDEX_COLUMN --recursive no

To confirm whether all target objects are flushed correctly, you can check query log:

    > io_flush --recursive "dependent" --target_name "Users"
    :000000000000000 flush[Users]
    :000000000000000 flush[Terms]
    :000000000000000 flush[Terms.users_name]
    :000000000000000 flush[Users.name]
    :000000000000000 flush[(anonymous:table:dat_key)]
    :000000000000000 flush[(anonymous:column:var_size)]
    :000000000000000 flush[(anonymous:table:hash_key)]
    :000000000000000 flush[(anonymous:column:var_size)]
    :000000000000000 flush[(DB)]
    <000000000000000 rc=0

In above example, specified not only `Users` table, related lexicon table `Terms` and index column `Terms.users_name` (data source is `Users.name`) are also flushed.

`flush[(anonymous:...)]` and `flush[(DB)]` means that Groonga’s internal objects are also flushed.

Log | Description
--- | ---
`flush[(anonymous:table:dat_key)]` | The internal object names in DB are flushed. If `GRN_DB_KEY=pat` is set, `TABLE_PAT_KEY` is used instead.
`flush[(anonymous:column:var_size)]` (logged as first `(anonymous:column:var_size)` object) | The internal object metadata (builtin types, token filter and so on) are flushed. This is a variable sized column which stores the above internal object metadata.
`flush[(anonymous:table:hash_key)]` | The internal configuration objects (which is set by `config_set`) are flushed.
`flush[(anonymous:column:var_size)]` (logged as second `(anonymous:column:var_size)` object) | The internal object metadata (options about internal objects such as specified tokenizer options) are flushed. This is a variable sized column which stores the above internal object metadata.
`flush[(DB)]` | The DB changes (lock acquired during `io_flush`) are flushed.

#### 7.3.24.4.2.3. `only_opened`

New in version 7.0.4.

Specifies whether opened objects are only flushed.

If there is only one process that changes the target database, flush performance will be improved by specifying `yes` to `only_opened`. It skips needless flushes.

You can’t specify target_name with `only_opened` option. If you specify target_name, `only_opened` is ignored.

If you specify `yes` to `only_opened`, recursive is ignored.

`only_opened` value must be `yes` or `no`. `yes` means that opened objects are only flushed. `no` means that all target objects are flushed even they aren’t opened.

The following `io_flush` flushes all changes in database, all tables and all columns:

Execution example:

    io_flush --only_opened yes
    # [[0, 1337566253.89858, 0.000355720520019531], true]

## 7.3.24.5. 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`.