// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

[[configuration]]
= Configuring Apache Kudu

:author: Kudu Team
:imagesdir: ./images
:icons: font
:toc: left
:toclevels: 3
:doctype: book
:backend: html5
:sectlinks:
:experimental:

== Configure Kudu

=== Configuration Basics
To configure the behavior of each Kudu process, you can pass command-line flags when
you start it, or read those options from configuration files by passing them using
one or more `--flagfile=<file>` options. You can even include the
`--flagfile` option within your configuration file to include other files. Learn more about gflags
by reading link:https://gflags.github.io/gflags/[its documentation].

You can place options for masters and tablet servers into the same configuration
file, and each will ignore options that do not apply.

Flags can be prefixed with either one or two `-` characters. This
documentation standardizes on two: `--example_flag`.

=== Discovering Configuration Options
Only the most common configuration options are documented here. For a more exhaustive
list of configuration options, see the link:configuration_reference.html[Configuration Reference].

To see all configuration flags for a given executable, run it with the `--help` option.
Take care when configuring undocumented flags, as not every possible
configuration has been tested, and undocumented options are not guaranteed to be
maintained in future releases.

[[directory_configuration]]
=== Directory Configurations
Every Kudu node requires the specification of directory flags. The
`--fs_wal_dir` configuration indicates where Kudu will place its write-ahead
logs. The `--fs_metadata_dir` configuration indicates where Kudu will place
metadata for each tablet. It is recommended, although not necessary, that these
directories be placed on a high-performance drives with high bandwidth and low
latency, e.g. solid-state drives. If `--fs_metadata_dir` is not specified,
metadata will be placed in the directory specified by `--fs_wal_dir`. Since
a Kudu node cannot tolerate the loss of its WAL or metadata directories, it
may be wise to mirror the drives containing these directories in order to
make recovering from a drive failure easier; however, mirroring may increase
the latency of Kudu writes.

The `--fs_data_dirs` configuration indicates where Kudu will write its data
blocks. This is a comma-separated list of directories; if multiple values are
specified, data will be striped across the directories. If not specified, data
blocks will be placed in the directory specified by `--fs_wal_dir`. Note that
while a single data directory backed by a RAID-0 array will outperform a single
data directory backed by a single storage device, it is better to let Kudu
manage its own striping over multiple devices rather than delegating the
striping to a RAID-0 array.

Additionally, `--fs_wal_dir` and `--fs_metadata_dir` may be the same as _one
of_ the directories listed in `--fs_data_dirs`, but must not be sub-directories
of any of them.

WARNING: Each directory specified by a configuration flag on a given machine
should be used by at most one Kudu process. If multiple Kudu processes on the
same machine are configured to use the same directory, Kudu may refuse to start
up.

WARNING: Once `--fs_data_dirs` is set, extra tooling is required to change it.
For more details, see the link:administration.html#change_dir_config[Kudu
Administration docs].

NOTE: The `--fs_wal_dir` and `--fs_metadata_dir` configurations can be changed,
provided the contents of the directories are also moved to match the flags.

=== Configuring the Kudu Master
To see all available configuration options for the `kudu-master` executable, run it
with the `--help` option:
----
$ kudu-master --help
----

[cols="m,d,m,d"]
.Supported Configuration Flags for Kudu Masters
|===
| Flag      | Valid Options     | Default     | Description

|--master_addresses | string | localhost |  Comma-separated list of all the RPC
addresses for Master consensus-configuration. If not specified, assumes a standalone Master.
|--fs_data_dirs | string | | List of directories where the Master will place its data blocks.
|--fs_metadata_dir | string | | The directory where the Master will place its tablet metadata.
|--fs_wal_dir | string | | The directory where the Master will place its write-ahead logs.
|--log_dir | string | /tmp | The directory to store Master log files.
|===

For the full list of flags for masters, see the
link:configuration_reference.html#kudu-master_supported[Kudu Master Configuration Reference].

=== Configuring Tablet Servers
To see all available configuration options for the `kudu-tserver` executable,
run it with the `--help` option:
----
$ kudu-tserver --help
----

.Supported Configuration Flags for Kudu Tablet Servers
|===
| Flag      | Valid Options     | Default     | Description

|--fs_data_dirs | string |  | List of directories where the Tablet Server will place its data blocks.
|--fs_metadata_dir | string |  | The directory where the Tablet Server will place its tablet metadata.
|--fs_wal_dir | string | | The directory where the Tablet Server will place its write-ahead logs.
|--log_dir | string | /tmp | The directory to store Tablet Server log files
|--tserver_master_addrs | string | `127.0.0.1:7051` |  Comma separated
addresses of the masters which the tablet server should connect to. The masters
do not read this flag.
|--block_cache_capacity_mb | integer | 512 | Maximum amount of memory allocated to the Kudu Tablet Server's block cache.
|--memory_limit_hard_bytes | integer | 4294967296 | Maximum amount of memory a Tablet Server can consume before it starts rejecting all incoming writes.
|===

For the full list of flags for tablet servers, see the
link:configuration_reference.html#kudu-tserver_supported[Kudu Tablet Server Configuration Reference].

== Configure Kudu Tables
Kudu allows certain configurations to be set per table. To configure the behavior of a Kudu table,
you can set these configurations at table creation, or alter them via the Kudu API or Kudu command
line tool.

.Supported Configurable Properties for Kudu Tables
|===
| Configuration      | Valid Options     | Default     | Description

| kudu.table.history_max_age_sec | integer | | Number of seconds to retain history for tablets in this table.
| kudu.table.maintenance_priority | integer | 0 | Priority level of a table for maintenance.
|===

== Next Steps
- link:quickstart.html[Get Started With Kudu]
- link:developing.html[Developing Applications With Kudu]