VoltDB
9.3.6
January 15, 2021 (updated January 18, 2021)
This document provides information about known issues and limitations to the current release of VoltDB. If you encounter any problems not listed below, please be sure to report them to support@voltdb.com. Thank you.
The process for upgrading from the recent versions of VoltDB is as follows:
Shutdown the database, creating a final snapshot (using voltadmin shutdown --save).
Upgrade the VoltDB software.
Restart the database (using voltdb start).
For DR clusters, see the section on "Upgrading VoltDB Software" in the VoltDB Administrator's Guide for special considerations related to DR upgrades. If you are upgrading from versions before V6.8, see the section on "Upgrading Older Versions of VoltDB Manually" in the same manual.
For customers upgrading from V8.x or earlier releases of VoltDB, please see the V8.0 Upgrade Notes.
For customers upgrading from V7.x or earlier releases of VoltDB, please see the V7.0 Upgrade Notes.
For customers upgrading from V6.x or earlier releases of VoltDB, please see the V6.0 Upgrade Notes.
Users of previous versions of VoltDB should take note of the following changes that might impact their existing applications.
1. Release V9.3.6 (January 15, 2021) | |
1.1. | Recent improvements |
The following limitations in previous versions have been resolved:
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2. Release V9.3.5 (December 23, 2020) | |
2.1. | Recent improvements |
The following limitations in previous versions have been resolved:
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3. Release V9.3.4 (November 13, 2020) | |
3.1. | Recent improvements |
The following limitations in previous versions have been resolved:
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4. Release V9.3.3 (October 21, 2020) | |
4.1. | Improved performance for DR DROP command |
The voltadmin DR DROP command removes a cluster from a cross datacenter replication conversation. Previously, this procedure could take up to 90 seconds. The command has been optimized to significantly reduce the time it takes to complete. | |
4.2. | Recent improvements |
The following limitations in previous versions have been resolved:
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5. Release V9.3.2 (July 7 2020) | |
5.1. | Support for RHEL and CentOS version 8 |
VoltDB has completed testing and qualification of the Red Hat Enterprise and CentOS version 8 operating systems as supported platforms for running VoltDB in development and production. | |
5.2. | Recent improvements |
The following limitations in previous versions have been resolved: Save and Restore:
Monitoring:
Export:
Other:
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6. Release V9.3.1 (May 1, 2020) | |
The current release finalizes two beta features introduced in 9.2, scheduled tasks and configuration of flush intervals. In addition, this release includes the following new features and improvements. | |
6.1. | Export Improvements |
The export subsystem has been rewritten to provide significant improvements in both performance and reliability, as well as accommodate planned future enhancements. The new subsystem is available to all customers using the VoltDB Enterprise Edition. The key advantages of the new export subsystem are:
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6.2. | Custom tasks |
VoltDB 9.2 introduced tasks, which let you schedule stored procedures for execution on a repeating schedule. Tasks are now complete and ready for production use. In addition, this release extends support to include custom tasks, where you can dynamically adjust the procedure called, the parameters to that procedure, the interval between calls, or any combination of the three based on the results of the previous invocation. You write custom tasks as Java classes that set the attributes of the next task run and identify a callback method to invoke once the procedure completes. See the chapter on custom tasks in the VoltDB Guide to Performance and Customization for details. There is also a sample custom task available in the VoltDB github repository. | |
6.3. | Thread pools |
The VoltDB Enterprise Edition now lets you control the thread pools used to execute the export subsystem. A thread pool defines the number of threads used to run processes concurrently. The more threads available, the more concurrent processes and therefore the more throughput. However, more threads means more system resources are consumed. Thread pools let you tune the export subsystem to balance throughput and resource utilization against your application requirements. You specify the thread pools in the database configuration file. You can define a default thread pool for export connectors, using the <export defaultpoolsize="2"> <configuration target="log" type="file" threadpool="logpool"> <property name="type">csv</property> <property name="nonce">Myapp</property> </configuration> </export> <threadpools> <pool name="logpool" size="5"/> </threadpools> | |
6.4. | Improved handling of non-deterministic procedures |
When using K-safety, it is important that stored procedures produce deterministic results so multiple copies of a partition can run transactions concurrently with predictable results. Without consistent results in every partition, the data could diverge. To avoid this, traditionally VoltDB would stop the database if a non-deterministic result was detected (referred to as a "hash mismatch" in the log file and error messages). Writing deterministic stored procedures is still important. But VoltDB now takes less disruptive action when divergence is detected. Rather than stopping the database every time a mismatch is detected, in most cases VoltDB now shuts down the extra copies of the partitions and runs in a single-copy reduced mode, eliminating the possibility of divergence. Of course, in the reduced mode, the cluster is no longer K-safe, which should be corrected as soon as possible. But until the offending procedure can be replaced and the cluster restarted, the database will continue to run and continue to process transactions. | |
6.5. | Large schema |
VoltDB easily handles databases with large numbers of tables. However, the schema also contains any stored procedures and auxiliary class JAR files loaded into the database. For databases using extremely large JAR files — most noticeably databases including machine learning (ML) models — it was possible to exceed the database's 50MB limit for the schema. VoltDB has now been rewritten to accommodate schema of arbitrary size. Note, however, that limitations on the size of individual tables (that is, no more than 1,024 columns per table and not to exceed 2MB for each table) are still in effect. | |
6.6. | Java 11 performance testing |
In addition to the reliability tests that are run on an ongoing basis, Java 11 was run through a series of performance tests to assess its impact on VoltDB, with a particular focus on the different garbage collection schemes. It turns out that all of the garbage collectors available in Java 11 perform as well or better than previous versions, in several tests notably reducing the size and frequency of GC pauses. | |
6.7. | Improved performance for schema changes |
Schema changes (and configuration updates) must be treated as multi-partition transactions in VoltDB. As a result, frequent schema changes can impact ongoing throughput and latency. This is particularly noticeable for large schema. Version 9.3 provides performance improvements to reduce the time required to apply schema changes and, as a result, reduce the impact on application latency. | |
6.8. | New Relic enhancements |
The current release improves the content and structure of VoltDB performance and management data provided to the New Relic monitoring suite. | |
6.9. | SNMP improvements |
All SNMP traps are now recorded in the log file. Previously, SNMP traps were sent, but not recorded. Log entries provide additional confirmation that SNMP events are triggered. | |
6.10. | LIMIT PARTITION ROWS deprecated |
The LIMIT PARTITION ROWS clause of the CREATE TABLE statement is being deprecated. LIMIT PARTITION ROWS was designed to avoid data overflowing the available space in the database. However, it was an all-or-nothing setting: once you exceeded the limit the database was automatically paused. Transactions could not continue until you manually reduced the row count. The feature itself did nothing to resolve the situation. LIMIT PARTITION ROWS is being deprecated and replaced by two significantly better capabilities now available in VoltDB. USING TTL lets you automatically and incrementally purge old data from tables and scheduled tasks let you build complex responsive algorithms for monitoring, managing, and resolving data volumes. Although still available in V9.3, customers should replace any use of the LIMIT PARTITION ROWS clause at their earliest convenience, because the syntax will be removed from the product in a future major release. | |
6.11. | Old export API deprecated |
In VoltDB V8.0, the interface for writing custom export clients was updated and replaced with a new API. To accommodate old clients, the export system uses the method signatures to distinguish between the old and new interface. However, the old interface is now being deprecated and support will be removed in the next major release. Any custom clients that use the old signature, where the onBlockStart() andonBlockCompletion() accept no arguments and processRow() expects two, should be updated to use the new interface. See the chapter on custom export and import in the VoltDB Guide to Performance and Customization for information on the new interface. | |
6.12. | RabbitMQ support is deprecated |
The export connector for RabbitMQ is now deprecated and will be removed in a future release. | |
6.13. | Security Notice |
The following libraries used by VoltDB have been updated to ensure the latest security and performance patches are applied:
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6.14. | Additional improvements |
In addition to the new features and capabilities described above, the following limitations in previous versions have been resolved:
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7. Release V9.2.2 (December 12, 2019) | |
7.1. | Maven improvements |
The packaging of VoltDB in the Maven Central Repository has been adjusted to ensure the correct artifacts are provided. | |
8. Release V9.2.1 (December 8, 2019) | |
8.1. | Improved handling of SSL/TLS connections in the JDBC interface |
The handling of secure export connections (using SSL/TLS) through the JDBC interface has been improved. Specifically, the requirement for a truststore when using a commercial certificate has been removed. | |
9. Release V9.2 (October 28, 2019) | |
This section describes new features in VoltDB V9.2 and known issues that have been fixed. Several new features are identified as beta software. Beta software means that the features are fully functional but have not received sufficient real-world usage or integration testing to ensure production readiness. We do not recommend using Beta features in production. However, we encourage you to try them and provide feedback on their usefulness to your business needs. Thank you. | |
9.1. | Change to Kafka export default behavior |
The Kafka Existing customers who use Kafka export but do not explicitly set the | |
9.2. | Export from tables ready for general use |
VoltDB 9.1 introduced two new beta features: the ability to export data directly from tables using the CREATE TABLE... EXPORT TO TARGET statement and the MIGRATE statement to simplify the export and deletion of records. These features are now fully supported for production use. | |
9.3. | Scheduling stored procedures as repetitive tasks (BETA) |
VoltDB 9.2 introduces a new feature, scheduled tasks. Tasks let you schedule the repeated execution of stored procedures at a set interval or using a cron-style declaration. You schedule tasks using the CREATE TASK statement. There is also a corresponding @Statistics selector, TASK, and ALTER TASK and DROP TASK statements. See the section on scheduling tasks or the reference pages describing each statement in the Using VoltDB manual for details. | |
9.4. | Directed procedures for distributing transactions to every partition |
One aspect of scheduling tasks is defining how they run; that is, as a single multi-partition transaction or
as separate transactions on each partition. To support the latter execution model, a new type of stored procedure is
being introduced, the directed procedure. Directed procedures are partitioned procedures in
that each instance of the procedure runs on a separate partition. However, directed procedures do not have a
specific partitioning value. You use the CREATE TASK statement or the Java
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9.5. | New Export tab and statistics in VMC |
The VoltDB Management Center (VMC) has a new tab, Export, which provides enhanced statistics and graphs that help analyze the performance of export connectors. | |
9.6. | User-defined aggregate functions (BETA) |
The CREATE FUNCTION statement lets you declare a user-defined scalar function. Starting with VoltDB 9.2, you can develop and declare user-defined aggregate functions as well using the CREATE AGGREGATE FUNCTION statement. Aggregate functions process data from multiple rows and return a single aggregated value. See the chapter on user-defined functions in the VoltDB Guide to Performance and Customization for details. | |
9.7. | Ability to query, filter and merge statistics using SQL (BETA) |
You can now query statistics from the VoltDB @Statistics system procedure as if the results were SQL tables. You can use the querystats directive in sqlcmd or the new @QueryStats system procedure specifying the column names from the @Statistics results in the selection expression. For example, the following sqlcmd command aggregates the row count from all of the partitions for each table using the TABLE selector: $ sqlcmd 1> querystats select table_name, sum(tuple_count) from statistics(table,0) group by table_name; Note that not all SQL syntax is supported as input to the querystats parser and for the initial release any syntax errors are reported in the server log but not reported to the user's console. See the descriptions of sqlcmd or the @QueryStats system procedure in the Using VoltDB manual for further details. | |
9.8. | Configurable flush intervals for DR and export buffers (BETA) |
You can now control how frequently the buffers for database replication (DR) and export are flushed. Normally, DR and export data is buffered until a certain amount of data is ready and then the data is sent as a batch. To avoid small amounts of data lingering in the buffer, there is a time limit after which, the data is sent even if the full batch size has not been reached. This time limit is called the "flush interval". You can now control these settings in the configuration file by setting a system-wide minimum and separate flush intervals for DR and export. See the VoltDB Administrator's Guide for details on configuring flush intervals. | |
9.9. | Undocumented feature deprecated |
In conjunction with the new configuration options for flushing buffers, an older undocumented attribute for setting the DR flush interval is being deprecated. The flushInterval attribute of the <dr> element is deprecated and will be removed in a future major release. In the meantime, this attribute will continue to operate and will supersede the new settings and defaults, so as not to change existing behavior for any customers who may have used this feature. However, those users are strongly encouraged to switch to the new, supported feature at their earliest convenience to avoid problems when the deprecated attribute is removed from the product in the future. | |
9.10. | Additional improvements |
In addition to the new features and capabilities described above, the following limitations in previous versions have been resolved:
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10. Release V9.1.1 (September 3, 2019) | |
10.1. | Licensing change for the VoltDB client in Maven. |
The license for the VoltDB JAR file in Maven has been changed from AGPL to an MIT license. | |
11. Release V9.1 (August 8, 2019) | |
11.1. | Reduce the size of a running cluster. |
Previously, you could expand a running cluster to increase capacity by starting the new server with the voltdb start --add command. However, until now there was no way to reduce the cluster size without stopping and reconfiguring the database. With the introduction of the voltadmin resize command, you can now elastically shrink a running cluster as well. The voltadmin resize command tests the cluster to make sure it can be reduced in size, tells you which nodes will be removed, and then starts the resize process. See the section on "Removing Nodes with Elastic Scaling" in the Using VoltDB manual for details on reducing the size of a running VoltDB cluster. | |
11.2. | MIGRATE TO TARGET finishes beta testing and is ready for production use. |
VoltDB V9.0 introduced migration as a beta feature, making it possible to automate the data lifecycle by migrating data to an external resource before deleting it from the VoltDB database. With V9.1, the migration feature is now fully integrated, tested, and extended to round out its capabilities. WarningThe syntax for the CREATE TABLE statement has changed from the original beta release. For consistency and to allow use without TTL, the MIGRATE TO TARGET clause now appears after the table name and before the column definitions, rather than after the USING TTL clause. If you used the MIGRATE TO TARGET clause during the beta test period, you will need to modify your schema and reload your database after installing V9.1. See the description of the CREATE TABLE statement in the Using VoltDB manual for details on automating the migration of data to external targets. | |
11.3. | New MIGRATE statement. |
Using the MIGRATE TO TARGET clause with USING TTL automates the export of data to an external target before the data is deleted. In addition, you can now use the MIGRATE TO TARGET clause by itself — without the USING TTL clause — for situations where you want to manually control when the data is migrated. To do this, you can use the new MIGRATE statement to manually initiate the migration during a transaction. Note that you can also use the MIGRATE to statement for tables defined with both MIGRATE TO TARGET and USING TTL, in which case an explicit MIGRATE statement can preemptively migrate the data before the TTL value is reached. See the description of the MIGRATE statement in the Using VoltDB manual for details. | |
11.4. | EXPORT TO TARGET for exporting data directly from tables (Beta Feature). |
VoltDB 9.1 introduces a new feature that makes it possible to connect tables (not just streams) to export targets. If a table is declared with the EXPORT TO TARGET clause, just like a stream, any data inserted into the table is passed to the export connector. This simplifies applications that want to stream incoming data to external systems, where previously there had to be both a table and a matching stream. WarningCREATE TABLE... EXPORT TO TARGET is a beta feature. All functionality is believed to be complete as described. However, it is possible individual aspects of the feature may change before it is deemed production ready. For that reason export directly from tables is not recommended for production use at this time. However, we encourage you to try it in development and welcome feedback on its usefulness. For example, the following table declaration allows any data inserted into the Alerts table to also be exported to the Messagelog target: CREATE TABLE Alerts
EXPORT TO TARGET Messagelog 15519
( eventtime TIMESTAMP,
sender VARCHAR(16),
message VARCHAR(128)
); You can also customize which events trigger export. Triggering events include inserts, updates (both before and after the update) and deletes. By default, only inserts trigger export; you can specify a different list of triggers with the ON clause: CREATE TABLE user
EXPORT TO TARGET userarchive
ON INSERT, UPDATE, DELETE
( username VARCHAR(128),
id BIGINT,
lastlogin TIMESTAMP
); See the description of the CREATE TABLE statement in the Using VoltDB manual for more information about associating tables with export targets. | |
11.5. | Improved handling of multi-partition transactions with large intermediate result sets |
VoltDB limits each transaction to 50 MB of results. In fact, each transaction fragment is limited to 50MB. However, for multi-partition transactions, this means each partition can return up to 50MB of data to the coordinator. For large clusters with many unique partitions, it is possible for all this data to exceed the allocated Java heap for the coordinator, causing that node to fail with an out of memory error. To avoid this situation, VoltDB now limits the amount of data each fragment can return, based on the current maximum heap size and number of partitions. By default, each partition in a multi-partition transaction is only allowed to return the lesser of 65% of the maximum heap size divided by the number of unique partitions (sitesperhost * number of nodes / k+1 ) or 50MB. The limit is further reduced for read-only multi-partition transactions to accommodate for the fact that multiple read-only transactions can be run simultaneously. If, at runtime, a fragment exceeds the limit, it throws an exception and the transaction rolls back gracefully. You can adjust this per-partition multi-partition response limit by setting the environment variable MP_MAX_TOTAL_RESP_SIZE. You can either set it as the percentage of max heap to use in the calculation (by using the percent sign) or as a specific number of bytes (by using an integer value with no suffix). For example, to allow a maximum of only 50% of the allowable heap size, you can set the following environment variable before starting the server: $ export MP_MAX_TOTAL_RESP_SIZE="50%"
$ voltdb start -D ~/mydb ... You can set MP_MAX_TOTAL_RESP_SIZE as an environment variable or as a Java system property through VOLTDB_OPTS: $ export VOLTDB_OPTS="-DMP_MAX_TOTAL_RESP_SIZE=50%"
$ voltdb start -D ~/mydb ... | |
11.6. | New command to show license information. |
There is a new command, voltadmin show license, that lists information about the current license in use by a running VoltDB cluster. You can get similar information programmatically using the @SystemInformation system procedure with the LICENSE selector. | |
11.7. | Additional improvements |
In addition to the new features and capabilities described above, the following limitations in previous versions have been resolved:
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12. Release V9.0 (April 11, 2019) | |
12.1. | Updated operating system and software requirements |
The requirements on the underlying operating system and software environment have been updated for VoltDB V9.0. The older CentOS and RHEL version 6.6 is no longer supported and Java 11 support has been added. In addition, support for kafka 0.8.2 has been dropped and Kafka import and export now requires version 0.10.2 or later. See the VoltDB Administrator's Guide for details on the platform requirements for running VoltDB clusters. | |
12.2. | Support for Java 11 |
VoltDB now supports both Java 8 and Java 11. | |
12.3. | Automated Deletion of Old Data |
VoltDB 8.4 introduced a new feature, USING TTL ("time to live"), that lets you define when records expire and can be deleted. This feature simplifies application design by automatically removing old data from the database based on settings you define in the table schema. With VoltDB 9.0, this feature is extended to include the migration of deleted data to other systems for archival purposes, as described next. | |
12.4. | New Export Capabilities |
The code that supports export of data to external systems has been rewritten to provide flexibility, improve reliability, reduce system resource utilization, and support new and future product features. The new export system reinforces the durability of data queued to the export connectors across unexpected system and network failures and allows export to be extended to add new capabilities. The first two new capabilities are:
Export now starts when the stream is defined, not when the target is defined. Previously, stream data was not queued for export until a valid export connector was configured and connected. Starting with VoltDB 9.0, data written to streams declared with the EXPORT TO TARGET clause are queued for export whether the target is configured or not. Similarly, the queued data is removed as soon as the stream itself is removed with the DROP STREAM statement. Also, export is now an enterprise feature. The VoltDB Community Edition provides access to two streams per database, so users have access to basic export functionality. But for unlimited access to export and migration features, the Enterprise Edition is required. | |
12.5. | "Live" Schema Updates with Database Replication |
Previously, database replication (DR) required the schema of the cooperating databases to match for all DR tables. So updating the schema required a pause while all of the affected databases were updated. Starting with 9.0, this limitation has been loosened. DR continues even if the schema are different. So it is possible to update the schema without interrupting ongoing transactions. Of course, it is not possible for VoltDB to resolve individual transactions if the schema differ. So if a DR consumer (either a replica in passive DR or an XDCR cluster in active replication) receives a binary log where the schema of the affected table(s) does not match, DR will stall and wait for the schema to be updated to match the incoming data. Therefore, care must be taken when updating the schema to ensure that no transactions that are affected by the schema change are processed during the interval when the clusters' schema do not match. See the sections on updating DR schema for passive and active DR for more information. | |
12.6. | Simplified JSON interface |
A new version of the VoltDB JSON API, 2.0, is now available. The original JSON interface provides complete information about the schema for the data being returned, including separate entries for the data, the column names, and datatypes. The 2.0 API returns a much more compact result set with each row represented by an associative array with each element consisting of the column name and value. | |
12.7. | New @Statistics selector IDLETIME |
There was an undocumented feature of the @Statistics system procedure that reported on how busy the execution queues for the individual partitions are. This data is now supported as the IDLETIME selector. See the description of the @Statistics system procedure in the Using VoltDB manual for details. | |
12.8. | JVM stats automatically disabled |
The I/O activity that JVM stats generates can interface with performance for applications like VoltDB, to the point where it can cause cluster nodes to disconnect. VoltDB now automatically disables JVM stats if /tmp is not defined as tmpfs (temporary in-memory storage). | |
12.9. | Changes to how export streams are reported |
Export streams (that is streams defined with the EXPORT TO TARGET clause) are no longer reported under the TABLE statistics of the @Statistics system procedure. Export streams are now reported under the EXPORT selector and tables and streams without export are reported under TABLE. | |
12.10. | Support for multiple schema and classes files when initializing the database root |
The voltdb init command now allows you to specify multiple files as arguments to the --schema and --classes flags. Separate multiple files with commas. You can also use the asterisk (*) as a wildcard character. For example, the following command initializes a root directory with two schema files, plus all the JAR files from one folder and another JAR file from the current working directory: $ voltdb init -D ~/mydb \ --schema=customers.sql,companies.sql \ --classes=storedprocs/*.jar,myfunctions.jar It is also possible to specify multiple schema and classes files when configuring VoltDB for use in
Kubernetes. See in the readme file in the | |
12.11. | Log4J logger JOIN has been renamed to ELASTIC |
The Log4J logger for elastic operations such as adding new cluster nodes on the fly has been renamed from JOIN to ELASTIC | |
12.12. | Security Notice |
The following change has been made to improve security and eliminate potential threats:
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12.13. | Additional improvements |
In addition to the new features and capabilities described above, the following limitations in previous versions have been resolved:
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The following are known limitations to the current release of VoltDB. Workarounds are suggested where applicable. However, it is important to note that these limitations are considered temporary and are likely to be corrected in future releases of the product.
The following notes provide details concerning how certain VoltDB features operate. The behavior is not considered incorrect. However, this information can be important when using specific components of the VoltDB product.