Known Issues and Limitations

Schema

Primary keys

  • Columns that are part of the primary key cannot be renamed. The primary key may not be changed after the table is created. You must drop and recreate a table to select a new primary key or rename key columns.

  • The columns which make up the primary key must be listed first in the schema.

  • The primary key of a row may not be modified using the UPDATE functionality. To modify a row’s primary key, the row must be deleted and re-inserted with the modified key. Such a modification is non-atomic.

  • Columns with DOUBLE, FLOAT, or BOOL types are not allowed as part of a primary key definition. Additionally, all columns that are part of a primary key definition must be NOT NULL.

  • Auto-generated primary keys are not supported.

  • Cells making up a composite primary key are limited to a total of 16KB after the internal composite-key encoding done by Kudu.

Columns

  • TIMESTAMP, DECIMAL, CHAR, VARCHAR, DATE, and complex types like ARRAY are not supported.

  • Type, nullability, compression, and encoding of existing columns cannot be changed by altering the table.

  • Tables can have a maximum of 300 columns.

Tables

  • Tables must have an odd number of replicas, with a maximum of 7.

  • Replication factor (set at table creation time) cannot be changed.

Cells (individual values)

  • Cells cannot be larger than 64KB.

Other usage limitations

  • Kudu is primarily designed for analytic use cases. You are likely to encounter issues if a single row contains multiple kilobytes of data.

  • Secondary indexes are not supported.

  • Multi-row transactions are not supported.

  • Relational features, like foreign keys, are not supported.

  • Identifiers such as column and table names are restricted to be valid UTF-8 strings. Additionally, a maximum length of 256 characters is enforced.

  • Dropping a column does not immediately reclaim space. Compaction must run first.

  • There is no way to run compaction manually, but dropping the table will reclaim the space immediately.

Partitioning Limitations

  • Tables must be manually pre-split into tablets using simple or compound primary keys. Automatic splitting is not yet possible. Range partitions may be added or dropped after a table has been created. See Schema Design for more information.

  • Data in existing tables cannot currently be automatically repartitioned. As a workaround, create a new table with the new partitioning and insert the contents of the old table.

  • Tablets that lose a majority of replicas (such as 1 left out of 3) require manual intervention to be repaired.

Cluster management

  • Rack awareness is not supported.

  • Multi-datacenter is not supported.

  • Rolling restart is not supported.

Server management

  • Production deployments should configure a least 4GB of memory for tablet servers, and ideally more than 10GB.

  • Write ahead logs (WAL) can only be stored on one disk.

  • Disk failures are not tolerated and tablets servers will crash as soon as one is detected.

  • Failed disks with unrecoverable data require the formatting of all the Kudu data for that tablet server before it can be started again.

  • Data directories cannot be added/removed; all must be reformatted to change the set of directories.

  • Tablet servers cannot be gracefully decommissioned.

  • Tablet servers can’t change address/port.

  • Kudu has a hard requirement on having up-to-date NTP. Kudu masters and tablet servers will crash when out of sync.

  • Kudu releases are only tested with NTP. Other time synchronization providers like Chrony may or may not work.

Scale

  • Recommended maximum number of tablet servers is 100.

  • Recommended maximum number of masters is 3.

  • Recommended maximum amount of stored data, post-replication and post-compression, per tablet server is 4TB.

  • Recommended maximum number of tablets per tablet server is 1000, post-replication.

  • Maximum number of tablets per table for each tablet server is 60, post-replication, at table-creation time.

Replication and Backup Limitations

  • Kudu does not currently include any built-in features for backup and restore. Users are encouraged to use tools such as Spark or Impala to export or import tables as necessary.

Security Limitations

  • Authorization is only available at a system-wide, coarse-grained level. Table-level, column-level, and row-level authorization features are not available.

  • Data encryption at rest is not built in. Kudu has been reported to run correctly on systems using local block device encryption (e.g. dmcrypt).

  • Kudu server Kerberos principals must follow the pattern kudu/<HOST>@DEFAULT.REALM. Configuring an alternate Kerberos principal is not supported.

  • Kudu’s integration with Apache Flume does not support writing to Kudu clusters that require Kerberos authentication.

  • Kudu client instances retrieve authentication tokens upon first contact with the cluster. These tokens expire after one week. Use of a single Kudu client instance for more than one week is not supported.

Other Known Issues

The following are known bugs and issues with the current release of Kudu. They will be addressed in later releases. Note that this list is not exhaustive, and is meant to communicate only the most important known issues.

  • If the Kudu master is configured with the -log_force_fsync_all option, tablet servers and clients will experience frequent timeouts, and the cluster may become unusable.

  • If a tablet server has a very large number of tablets, it may take several minutes to start up. It is recommended to limit the number of tablets per server to 100 or fewer. Consider this limitation when pre-splitting your tables. If you notice slow start-up times, you can monitor the number of tablets per server in the web UI.