Apache Kudu 1.4.0 Release Notes

New features

  • The C++ and Java client libraries now support the ability to alter the storage attributes (e.g. encoding and compression) and default value of existing columns. Additionally, it is now possible to rename a column which is part of a table’s primary key.

  • The C++ client library now includes an experimental KuduPartitioner API which may be used to efficiently map rows to their associated partitions and hosts. This may be used to achieve better locality or distribution of writes in client applications.

  • The Java client library now supports enabling fault tolerance on scanners. Fault tolerant scanners are able to transparently recover from concurrent server crashes at the cost of some performance overhead. See the Java API documentation for more details on usage.

  • The kudu command line tool now includes a new advanced administrative command kudu remote_replica unsafe_change_config. This command may be used to force a tablet to perform an unsafe change of its Raft replication configuration. This can be used to recover from scenarios such as a loss of a majority of replicas, at the risk of losing edits.

  • The kudu command line tool now includes the kudu fs check command which performs various offline consistency checks on the local on-disk storage of a Kudu Tablet Server or Master. In addition to detecting various inconsistencies or corruptions, it can also detect and remove data blocks that are no longer referenced by any tablet but were not fully removed from disk due to a crash or a bug in prior versions of Kudu.

  • The kudu command line tool can now be used to list the addresses and identifiers of the servers in the cluster using either kudu master list or kudu tserver list.

  • Kudu 1.4 now includes the optional ability to compute, store, and verify checksums on all pieces of data stored on a server. Prior versions only performed checksums on certain portions of the stored data. This feature is not enabled by default since it makes a backward-incompatible change to the on-disk formats and thus prevent downgrades. Kudu 1.5 will enable the feature by default.

Optimizations and improvements

  • kudu cluster ksck now detects and reports new classes of inconsistencies and issues. In particular, it is better able to detect cases where a configuration change such as a replica eviction or addition is pending but is unable to be committed. It also now properly detects and reports cases where a tablet has no elected leader.

  • The default size for Write Ahead Log (WAL) segments has been reduced from 64MB to 8MB. Additionally, in the case that all replicas of a tablet are fully up to date and data has been flushed from memory, servers will now retain only a single WAL segment rather than two. These changes are expected to reduce the average consumption of disk space on the configured WAL disk by 16x, as well as improve the startup speed of tablet servers by reducing the number and size of WAL segments that need to be re-read.

  • The default on-disk storage system used by Kudu servers (Log Block Manager) has been improved to compact its metadata and remove dead containers. This compaction and garbage collection occurs only at startup. Thus, the first startup after upgrade is expected to be longer than usual, and subsequent restarts should be shorter.

  • The usability of the Kudu web interfaces has been improved, particularly for the case where a server hosts many tablets or a table has many partitions. Pages that list tablets now include a top-level summary of tablet status and show the complete list under a toggleable section.

  • The Maintenance Manager has been improved to improve utilization of the configured maintenance threads. Previously, maintenance work would only be scheduled a maximum of 4 times per second, but now maintenance work will be scheduled immediately whenever any configured thread is available. This can improve the throughput of write-heavy workloads.

  • The Maintenance Manager will now aggressively schedule flushes of in-memory data when memory consumption crosses 60% of the configured process-wide memory limit. The backpressure mechanism which begins to throttle client writes has been accordingly adjusted to not begin throttling until reaching 80% of the configured limit. These two changes together result in improved write throughput, more consistent latency, and fewer timeouts due to memory exhaustion.

  • Many performance improvements were made to write performance. Applications which send large batches of writes to Kudu should see substantially improved throughput in Kudu 1.4.

  • Several improvements were made to reduce the memory consumption of Kudu Tablet Servers which hold large volumes of data. The specific amount of memory saved varies depending on workload, but the expectation is that approximately 350MB of excess peak memory usage has been eliminated per TB of data stored.

  • The number of threads used by the Kudu Tablet Server has been reduced. Previously, each tablet used a dedicated thread to append to its WAL. Those threads now automatically stop running if there is no activity on a given tablet for a short period of time.

Fixed Issues

  • KUDU-2020 Fixed an issue where re-replication after a failure would proceed significantly slower than expected. This bug caused many tablets to be unnecessarily copied multiple times before successfully being considered re-replicated, resulting in significantly more network and IO bandwidth usage than expected. Mean time to recovery on clusters with large amounts of data is improved by up to 10x by this fix.

  • KUDU-1982 Fixed an issue where the Java client would call NetworkInterface.getByInetAddress very often, causing performance problems particularly on Windows where this function can be quite slow.

  • KUDU-1755 Improved the accuracy of the on_disk_size replica metrics to include the size consumed by bloom filters, primary key indexes, and superblock metadata, and delta files. Note that, because the size metric is now more accurate, the reported values are expected to increase after upgrading to Kudu 1.4. This does not indicate that replicas are using more space after the upgrade; rather, it is now accurately reporting the amount of space that has always been used.

  • KUDU-1192 Kudu servers will now periodically flush their log messages to disk even if no WARNING-level messages have been logged. This makes it easier to tail the logs to see progress output during normal startup.

  • KUDU-1999 Fixed the ability to run Spark jobs in "cluster" mode against Kudu clusters secured by Kerberos.

Wire Protocol compatibility

Kudu 1.4.0 is wire-compatible with previous versions of Kudu:

  • Kudu 1.4 clients may connect to servers running Kudu 1.0 or later. If the client uses features that are not available on the target server, an error will be returned.

  • Kudu 1.0 clients may connect to servers running Kudu 1.4 with the exception of the below-mentioned restrictions regarding secure clusters.

  • Rolling upgrade between Kudu 1.3 and Kudu 1.4 servers is believed to be possible though has not been sufficiently tested. Users are encouraged to shut down all nodes in the cluster, upgrade the software, and then restart the daemons on the new version.

The authentication features introduced in Kudu 1.3 place the following limitations on wire compatibility between Kudu 1.4 and versions earlier than 1.3:

  • If a Kudu 1.4 cluster is configured with authentication or encryption set to "required", clients older than Kudu 1.3 will be unable to connect.

  • If a Kudu 1.4 cluster is configured with authentication and encryption set to "optional" or "disabled", older clients will still be able to connect.

Incompatible Changes in Kudu 1.4.0

  • Kudu servers, by default, will now only allow unencrypted or unauthenticated connections from trusted subnets, which are private networks (,,,, and local subnets of all local network interfaces. Unencrypted or unauthenticated connections from publicly routable IPs will be rejected, even if encryption and authentication are not configured.

    The trusted subnets can be configured using the --trusted_subnets flag, which can be set to IP blocks represented in CIDR notation separated by comma. Set it to '' to allow unauthenticated connections from all remote IP addresses. However, if network access is not otherwise restricted by a firewall, malicious users may be able to gain unauthorized access. This can be mitigated if authentication and encryption are configured to be required.

Client Library Compatibility

  • The Kudu 1.4 Java client library is API- and ABI-compatible with Kudu 1.3. Applications written against Kudu 1.3 will compile and run against the Kudu 1.4 client library and vice-versa, unless one of the following newly added APIs is used:

    • [Async]KuduScannerBuilder.setFaultTolerant(…​)

    • New methods in AlterTableOptions: removeDefault, changeDefault, changeDesiredBlockSize, changeEncoding, changeCompressionAlgorithm

    • KuduClient.updateLastPropagatedTimestamp

    • KuduClient.getLastPropagatedTimestamp

    • New getters in PartialRow: getBoolean, getByte, getShort, getInt, getLong, getFloat, getDouble, getString, getBinaryCopy, getBinary, isNull, isSet.

  • The Kudu 1.4 C++ client is API- and ABI-forward-compatible with Kudu 1.3. Applications written and compiled against the Kudu 1.3 client library will run without modification against the Kudu 1.4 client library. Applications written and compiled against the Kudu 1.4 client library will run without modification against the Kudu 1.3 client library unless they use one of the following new APIs:

    • KuduPartitionerBuilder

    • `KuduPartitioner

    • KuduScanner::SetRowFormatFlags (unstable API)

    • KuduScanBatch::direct_data, KuduScanBatch::indirect_data (unstable API)

  • The Kudu 1.4 Python client is API-compatible with Kudu 1.3. Applications written against Kudu 1.3 will continue to run against the Kudu 1.4 client and vice-versa.

Known Issues and Limitations

Please refer to the Known Issues and Limitations section of the documentation.

Installation Options

For full installation details, see Kudu Installation.