Volt Active Data
12.1
VoltDB Operator 1.10.0 |
VoltDB Helm Chart 1.10.0 |
December 21, 2022 (updated January 16calendar, 2023)
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@voltactivedata.com. Thank you.
VoltDB 12 is a major release that includes several key features. First and foremost, the memory management for the database table data has been rewritten and optimized to reduce certain impediments in the previous implementation. Although this change is primarily internal and transparent to you as a customer, it does have two direct benefits in terms of eliminating development and operational roadblocks:
No Large Compaction Events — As tuples are inserted and deleted, small gaps of unused memory are created within the larger allocated blocks. Previously, if the total amount of allocated but unused memory hit a specific high watermark, the database would compact all of the table memory before continuing. As effective as this mechanism was, it could result in unpredictable latency spikes in the ongoing workload.
Now, defragmentation of data storage is performed incrementally on a per table and per partition basis. Since the compaction transactions are much smaller, and also partitioned, they have little or no impact on the ongoing business workload. In addition, you as the database administrator have control over how large those periodic compaction events are and and how often they occur. See the chapter on memory management in the Volt Performance and Customization Guide for more information about the new memory management algorithm.
No Hash Mismatches Due to Row Order — In the past, developers had to be careful not to introduce non-deterministic behavior into their stored procedures by performing unordered queries. The issue was that, when using K-Safety, different copies of a partition could return results in a different order if you did not include the appropriate ORDER BY clause.
A key aspect of the memory management scheme introduced in V12.0 is that all copies of a partition now always return a query's results in one, deterministic order, even if the query itself is not sorted. This means that queries without an appropriate ORDER BY clause will not cause a hash mismatch.
Mind you, including an ORDER BY clause is still recommended so you can depend on the order in which the results are returned. Although VoltDB now returns results in a deterministic order, you do not know what that order will be. Also, although the new deterministic row order helps, there are other practices (such as calling system-specific time functions) that still cause hash mismatches and must be avoided. See the section on stored procedures and determinism in the Using VoltDB manual for a reminder of what to watch out for.
Other new features introduced in V12.0 and recent releases include:
Support for Ubuntu 22.04 and the Rocky OS — Volt Active Data has added Ubuntu 22.04 and Rocky OS as supported platforms for VoltDB.
Support for storing TLS/SSL credentials in Kubernetes secrets — When enabling TLS/SSL in Kubernetes, you can now store your TLS/SSL credentials (including the keystore, truststore, and passwords) in a Kubernetes secret. This avoids having to specify passwords on the Helm command line and simplifies the commands needed to start and update database instances. See the section on configuring TLS/SSL in the Volt Kubernetes Administrator's Guide for details.
Expiration dates for user accounts — You can now specify an expiration date for user accounts in the database configuration file. Once the specified date is past, the associated account can no longer access the database, until the configuration for the user account is updated. The expiration date is optional. See the section on defining users and roles in the Using VoltDB manual for details.
New LAG() windowing function — The LAG() function accesses previous rows from the window results using an offset. See the section on windowing functions in the SELECT reference page for more information.
Dedicated pod for VMC and HTTP API in Kubernetes — By default, Volt in
Kubernetes now creates a separate pod for the Volt Management Center (VMC) and HTTP API. This provides a single service
name for accessing these resources, as well as a single instance for the entire cluster (rather than separate instances
for each host). The new pod is available from the service name {release-name}-voltdb-vmc
where
{release-name} is the name of the Helm release for the database cluster.
Most of the new features and capabilities in VoltDB V12.0 do not impact existing applications. However, there are a few changes that require action for users upgrading from earlier versions. Also several deprecated features have now been removed. Existing customers should take note of of the following changes:
A license is required on the voltdb init command
Starting with V12, the voltdb init command must find and load a license file or the
initialization of the database root directory will fail. The license file can either be specified explicitly using the
-l
or --license
flag or it can be found in one of the three default locations (the
current working directory, the user's home directory, or the voltdb
folder where VoltDB is
installed). It is still possible to specify a license file on the voltdb start command — in
case you need to change or update the license after initialization — but a license must be specified on the
voltdb init command first.
The utility kafkaloader10 is now deprecated
To support different versions of the Kafka API, two versions of the kafkaloader utility were provided in the past: kafkaloader and kafkaloader10. Now that support for older versions of Kafka has been dropped, the legacy loader, kafkaloader10, has been deprecated and will be removed in a future release.
Old deprecated methods removed from the Java client API
Several obsolete methods in the Java client API that were previously deprecated have now been removed. Those
methods were setClientAffinity
, setSendReadsToReplicas
, and
setReconnectOnConnectionLoss
.
The voltadmin plan_upgrade command has been removed
The procedure for upgrading the VoltDB software using limited hardware is no longer supported. The associated command, plan_upgrade, has been removed from the voltadmin utility.
@Statistics DRCONSUMER column renamed
The results of the @Statistics system procedure DRCONSUMER selector have been altered slightly. Specifically, the last column of the third results table has been renamed to be more descriptive from LAST_FAILURE to LAST_FAILURE_CODE.
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 Kubernetes, see the section on "Upgrading the VoltDB Software and Helm Charts" in the VoltDB Kubernetes Administrator's Guide. 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.
Finally, for all customers upgrading from earlier versions of VoltDB, please be sure to read the upgrade notes for your current and subsequent releases, including V6, V7, V8, and V10.
In addition to the major enhancements listed above, users of previous versions of VoltDB should take note of the following changes that might impact their existing applications. See the VoltDB Operator Release Notes for changes specific to the use of VoltDB on the Kubernetes platform.
1. Release V12.1 (December 21, 2022, updated December 29, 2022) | |
1.1. | Simplified updating of TLS/SSL certificates in Kubernetes eliminates need for cluster restart |
The latest Operator release simplifies the process for updating TLS/SSL certificates and eliminates the need to stop and restart the cluster to apply the new certificate. In Kubernetes,if you store the TLS/SSL credentials using Kubernetes secrets, either created manually or through the cert-manager, the Operator now automatically updates the configuration on the running cluster once the secret changes. So, if you created the secret manually, you simply need to delete and recreate the secret with the new credentials. If you use cert-manager, cert-manager itself updates the credentials when the expiration date approaches. In either case, the Operator recognizes the change and updates the running cluster without any further operator intervention. | |
1.2. | New @Statistics selector for information about the cluster nodes and the partitions they host |
The @Statistics system procedure has a new selector, HOST, that returns information about the nodes of the cluster, including what partitions it hosts and whether it is safe to stop the node in a K-safe cluster. See the description of the @Statistics system procedure in the Using VoltDB manual for details. | |
1.3. | New @SystemInformation selector for listing environment variables |
Support for a new selector, ENV, has been added to the @SystemInformation system procedure. The ENV selector returns information about the environment variables defined for the database server process, one row for each variable on each host. See the description of the @SystemInformation system procedure in the Using VoltDB manual for details. | |
1.4. | TLS/SSL protocols 1.0 and 1.1 are no longer supported |
The TLS/SSL protocol versions 1.0 and 1.1 were deprecated and removed from most industry applications and browsers in 2020. Going forward, these obsolete protocol versions are no longer available in VoltDB either. | |
1.5. | Additional improvements |
The following limitations in previous versions have been resolved:
| |
2. Release V12.0 (October 18, 2022) | |
2.1. | Additional information in @SystemInformation output |
The @SystemInformation system procedure now includes additional information regarding the number of processors, both existing and available for use. This is important because in certain situations (most notably, Kubernetes) not all processors are available to the application. The new results field is called JAVAAVAILABLEPROCESSORS. | |
2.2. | Additional improvements |
The following limitations in previous versions have been resolved:
|
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.
1. IPv6 | |
1.1. | Support for IPv6 addresses |
VoltDB works in IPv4, IPv6, and mixed network environments. Although the examples in the documentation use IPv4 addresses, you can use IPv6 when configuring your database, making connections through applications, or using the VoltDB command line utilities, such as voltdb and voltadmin. When specifying IPv6 addresses on the command line or in the configuration file, be sure to enclose the address in square brackets. If you are specifying both an IPv6 address and port number, put the colon and port number after the square brackets. For example: voltadmin status --host=[2001:db8:85a3::8a2e:370:7334]:21211 | |
2. VoltDB Management Center | |
2.1. | Schema updates clear the stored procedure data table in the Management Center Monitor section |
Any time the database schema or stored procedures are changed, the data table showing stored procedure statistics at the bottom of the Monitor section of the VoltDB Management Center get reset. As soon as new invocations of the stored procedures occur, the statistics table will show new values based on performance after the schema update. Until invocations occur, the procedure table is blank. | |
3. SQL | |
3.1. | You cannot partition a table on a column defined as ASSUMEUNIQUE. |
The ASSUMEUNIQUE attribute is designed for identifying columns in partitioned tables where the column values are known to be unique but the table is not partitioned on that column, so VoltDB cannot verify complete uniqueness across the database. Using interactive DDL, you can create a table with a column marked as ASSUMEUNIQUE, but if you try to partition the table on the ASSUMEUNIQUE column, you receive an error. The solution is to drop and add the column using the UNIQUE attribute instead of ASSUMEUNIQUE. | |
3.2. | Adding or dropping column constraints (UNIQUE or ASSUMEUNIQUE) is not supported by the ALTER TABLE ALTER COLUMN statement. |
You cannot add or remove a column constraint such as UNIQUE or ASSUMEUNIQUE using the ALTER TABLE ALTER COLUMN statement. Instead to add or remove such constraints, you must first drop then add the modified column. For example: ALTER TABLE employee DROP COLUMN empID; ALTER TABLE employee ADD COLUMN empID INTEGER UNIQUE; | |
3.3. | Do not use UPDATE to change the value of a partitioning column |
For partitioned tables, the value of the column used to partition the table determines what partition the row belongs to. If you use UPDATE to change this value and the new value belongs in a different partition, the UPDATE request will fail and the stored procedure will be rolled back. Updating the partition column value may or may not cause the record to be repartitioned (depending on the old and new values). However, since you cannot determine if the update will succeed or fail, you should not use UPDATE to change the value of partitioning columns. The workaround, if you must change the value of the partitioning column, is to use both a DELETE and an INSERT statement to explicitly remove and then re-insert the desired rows. | |
3.4. | Ambiguous column references no longer allowed. |
Starting with VoltDB 6.0, ambiguous column references are no longer allowed. For example, if both the Customer and Placedorder tables have a column named Address, the reference to Address in the following SELECT statement is ambiguous: SELECT OrderNumber, Address FROM Customer, Placedorder . . . Previously, VoltDB would select the column from the leftmost table (Customer, in this case). Ambiguous column references are no longer allowed and you must use table prefixes to disambiguate identical column names. For example, specifying the column in the preceding statement as Customer.Address. A corollary to this change is that a column declared in a USING clause can now be referenced using a prefix. For example, the following statement uses the prefix Customer.Address to disambiguate the column selection from a possibly similarly named column belonging to the Supplier table: SELECT OrderNumber, Vendor, Customer.Address FROM Customer, Placedorder Using (Address), Supplier . . . | |
4. Runtime | |
4.1. | File Descriptor Limits |
VoltDB opens a file descriptor for every client connection to the database. In normal operation, this use of file descriptors is transparent to the user. However, if there are an inordinate number of concurrent client connections, or clients open and close many connections in rapid succession, it is possible for VoltDB to exceed the process limit on file descriptors. When this happens, new connections may be rejected or other disk-based activities (such as snapshotting) may be disrupted. In environments where there are likely to be an extremely large number of connections, you should consider increasing the operating system's per-process limit on file descriptors. | |
4.2. | Use of Resources in JAR Files |
There are two ways to access additional resources in a VoltDB database. You can place the resources in the
LOAD CLASSES is used primarily to load classes associated with stored procedures and user-defined functions. However, it will also load any additional resource files included in subfolders of the JAR file. You can remove classes that are no longer needed using the REMOVE CLASSES directive. However, there is no explicit command for removing other resources. Consequently, if you rename resources or move them to a different location and reload the JAR file, the database will end up having multiple copies. Over time, this could result in more and more unnecessary memory being used by the database. To remove obsolete resources, you must first reinitialize the database root directory, start a fresh database, reload the schema (including the new JAR files with only the needed resources) and then restore the data from a snapshot. | |
4.3. | Servers with Multiple Network Interfaces |
If a server has multiple network interfaces (and therefore multiple IP addresses) VoltDB will, by default, open ports on all available interfaces. You can limit the ports to an single interface in two ways:
Also, when using an IP address to reference a server with multiple interfaces in command line utilities (such as voltadmin stop node), use the @SystemInformation system procedure to determine which IP address VoltDB has selected to identify the server. Otherwise, if you choose the wrong IP address, the command might fail. | |
5. Platforms | |
5.1. | OpenShift and Transparent Huge Pages (THP) |
For production, VoltDB requires that Transparent Huge Pages (THP) are disabled because they interfere with memory-intensive applications. However, THP may be enabled on OpenShift containers and the containers themselves not have permission to disable them. To overcome this situation, you must run the Helm chart for disabling THP from a privileged container: $ helm -n kube-system install thp voltdb/transparent-hugepages \ --set thp.securityContext.privileged=true | |
5.2. | Kubernetes Compatibility |
See the Volt Kubernetes Compatibility Chart for information on which versions of the Volt Operator and Helm charts support which version of VoltDB. See the VoltDB Operator Release Notes for additional information about individual releases of the VoltDB Operator. |