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.
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
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.
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
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.
CHAR, VARCHAR, DATE, and complex types like ARRAY, MAP, and STRUCT are not supported.
Type and nullability of existing columns cannot be changed by altering the table.
The precision and scale of
DECIMAL columns cannot be changed by altering the table.
Tables can have a maximum of 300 columns by default.
Tables must have an odd number of replicas, with a maximum of 7.
Replication factor (set at table creation time) cannot be changed.
Cells cannot be larger than 64KB before encoding or compression.
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.
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.
Rolling restart is not supported.
Recommended maximum point-to-point latency within a Kudu cluster is 20 milliseconds.
Recommended minimum point-to-point bandwidth within a Kudu cluster is 10 Gbps.
If you intend to use the location awareness feature to place tablet servers in different locations, it is recommended to measure the bandwidth and latency between servers to ensure they fit within the above guidelines.
All masters must be started at the same time when the cluster is started for the very first time.
Production deployments should configure a least 4 GiB of memory for tablet servers, and ideally more than 16 GiB when approaching the data and tablet Scale limits.
Write ahead logs (WAL) can only be stored on one disk.
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.
Kudu is known to run seamlessly across a wide array of environments and workloads with minimal expertise and configuration at the following scale:
3 master servers
100 tablet servers
8 TiB of stored data per tablet server, post-replication and post-compression.
1000 tablets per tablet server, post-replication.
60 tablets per table, per tablet server, at table-creation time.
10 GiB of stored data per tablet.
Staying within these limits will provide the most predictable and straightforward Kudu experience.
However, experienced users who run on modern hardware, use the latest versions of Kudu, test and tune Kudu for their use case, and work closely with the community, can achieve much higher scales comfortably. Below are some anecdotal values that have been seen in real world production clusters:
3 master servers
300+ tablet servers
10+ TiB of stored data per tablet server, post-replication and post-compression.
4000+ tablets per tablet server, post-replication.
50 GiB of stored data per tablet. Going beyond this can cause issues such a reduced performance, compaction issues, and slow tablet startup times.
Row-level authorization is not available.
Data encryption at rest is not directly built into Kudu. Encryption of
Kudu data at rest can be achieved through the use of local block device
encryption software such as
Kudu server Kerberos principals must follow the pattern
Configuring an alternate Kerberos principal is not supported.
The highest supported version of the TLS protocol is TLSv1.2
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 1000 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.