Upgrading to DataStax Enterprise 4.6

Follow these instructions to upgrade from DataStax Enterprise versions 3.2.5 to 4.5 to DataStax Enterprise 4.6.

Read and understand these instructions before upgrading. Carefully reviewing the planning and upgrade instructions can prevent errors and data loss.

Apache Cassandra® version change

Upgrading from DataStax Enterprise 3.2.5 to 4.6 includes a major Cassandra version change.

Be sure to follow the recommendations for upgrading the SSTables.

Upgrading SSTables is required for upgrades that contain major Apache Cassandra releases:

DataStax Enterprise 6.7 is compatible with Cassandra 3.11.
DataStax Enterprise 6.0 is compatible with Cassandra 3.11.
DataStax Enterprise 5.1 uses Cassandra 3.11.
DataStax Enterprise 5.0 uses Cassandra 3.0.
DataStax Enterprise 4.7 to 4.8 use Cassandra 2.1.
DataStax Enterprise 4.0 to 4.6 use Cassandra 2.0.

General recommendations

DataStax recommends backing up your data prior to any version upgrade, including logs and custom configurations. A backup provides the ability to revert and restore all the data used in the previous version if necessary.

OpsCenter provides a Backup Service that manages enterprise-wide backup and restore operations for DataStax Enterprise clusters. OpsCenter 6.5 and later is recommended.

Upgrade restrictions and limitations

Restrictions and limitations apply while a cluster is in a partially upgraded state.

With these exceptions, the cluster continues to work as though it were on the earlier version of DataStax Enterprise until all of the nodes in the cluster are upgraded.

General upgrade restrictions during an upgrade
- Do not enable new features.
- During the upgrade, do not bootstrap or decommission nodes.
- Do not issue these types of CQL queries during a rolling restart: DDL and TRUNCATE.
- Do not enable Change Data Capture (CDC) on a mixed-version cluster. Upgrade all nodes to DSE 5.1 or later before enabling CDC.
- Complete the cluster-wide upgrade before the expiration of gc_grace_seconds (approximately 13 days) to ensure any repairs complete successfully.

Nodes on different versions might show a schema disagreement during an upgrade.

DSE Graph nodes restrictions

Graph nodes have the same restrictions as the workload they run on. Do not alter graph schema during upgrades. Workload-specific restrictions apply for analytics and search nodes, such as no OLAP queries during upgrades.
Restrictions for DSE Analytic (Hadoop and Spark) nodes
- Do not run analytics jobs until all nodes are upgraded.
- Kill all Spark worker processes before you stop the node and install the new version.
- When upgrading to a major version of DSE, all nodes in a DSE datacenter that run Spark must be on the same version of Spark and the Spark jobs must be compiled for that version. Each datacenter acting as a Spark cluster must be on the same upgraded DSE version before reinitiating Spark jobs.
  
  In the case where Spark jobs run against Graph keyspaces, you must update all of the nodes in the cluster first to avoid Spark jobs failing.

Before you upgrade DSE Search or SearchAnalytics workloads, you must follow the specific tasks in the section.

DSE Search upgrade restrictions and limitations
- Do not update schemas.
- Do not reindex DSE Search nodes during upgrade.
- DSE 6.0 and later versions use a new Lucene codec. Segments written with this new codec cannot be read by earlier versions of DSE. To downgrade to earlier versions, the entire data directory for the search index in question must be cleared.
- DSE Search in DataStax Enterprise 6.7 uses Apache Solr 6.0. This significant change requires advanced planning and specific actions before and after the upgrade.
Restrictions for DSE Search (Solr) nodes
- Do not update schemas.
- Do not reindex DSE Search nodes during upgrade.
- Do not issue these types of queries during a rolling restart: BATCH or TRUNCATE.
- During the upgrade process on a cluster with mixed versions where DataStax Enterprise 4.7 or 4.8 supports pagination and earlier versions do not, issuing queries from the upgraded nodes returns only FetchSize results.
Restrictions for nodes using any kind of security
- Do not change security credentials or permissions until the upgrade is complete on all nodes.
- If you are not already using Kerberos, do not set up Kerberos authentication before upgrading. First upgrade the cluster, and then set up Kerberos.
Upgrading drivers and possible impact when driver versions are incompatible

Be sure to check driver compatibility. Depending on the driver version, you might need to recompile your client application code. See DataStax driver changes.

DataStax drivers come in two types:

DataStax drivers for DataStax Enterprise (DSE) — for use by DSE 4.8 and later

DataStax drivers for Apache Cassandra® — for use by Apache Cassandra and DSE 4.7 and earlier

While the DataStax drivers for Apache Cassandra drivers can connect to DSE 5.0 and later clusters, DataStax strongly recommends upgrading to the DSE drivers. The DSE drivers provide functionality for all DataStax Enterprise (DSE) features.

During upgrades, you might experience driver-specific impact when clusters have mixed versions of drivers. If your cluster has mixed versions, the protocol version is negotiated with the first host that the driver connects to. To avoid driver version incompatibility during upgrades, use one of these workarounds:

Protocol version: Because some drivers can use different protocol versions, force the protocol version at start up. For example, keep the Java driver at its current protocol version while the driver upgrade is happening. Switch to the Java driver to the new protocol version only after the upgrade is complete on all nodes in the cluster.
Initial contact points: Ensure that the list of initial contact points contains only hosts with the oldest driver version. For example, the initial contact points contain only Java driver v2. For details on protocol version negotiation, see protocol versions with mixed clusters in the Java driver version you are using, for example, Java driver.

DataStax Enterprise and Apache Cassandra configuration files

DataStax Enterprise (DSE) configuration files
Configuration file	Installer-Services and package installations	Installer-No Services and tarball installations
dse	/etc/default/dse (systemd) or /etc/init.d/ (SystemV)	N/A Node type is set via command line flags.
dse-env.sh	/etc/dse/dse-env.sh	<installation_location>/bin/dse-env.sh
byoh-env.sh	/etc/dse/byoh-env.sh	<installation_location>/bin/byoh-env.sh
dse.yaml	/etc/dse/dse.yaml	<installation_location>/resources/dse/conf/dse.yaml
logback.xml	/etc/dse/cassandra/logback.xml	<installation_location>/resources/logback.xml
spark-env.sh	/etc/dse/spark/spark-env.sh	<installation_location>/resources/spark/conf/spark-env.sh
spark-defaults.conf	/etc/dse/spark/spark-defaults.conf	<installation_location>/resources/spark/conf/spark-defaults.conf

Cassandra configuration files
Configuration file	Installer-Services and package installations	Installer-No Services and tarball installations
cassandra.yaml	/etc/dse/cassandra/cassandra.yaml	<installation_location>/conf/cassandra.yaml
cassandra.in.sh	/usr/share/cassandra/cassandra.in.sh	<installation_location>/bin/cassandra.in.sh
cassandra-env.sh	/etc/dse/cassandra/cassandra-env.sh	<installation_location>/conf/cassandra-env.sh
cassandra-rackdc.properties	/etc/dse/cassandra/cassandra-rackdc.properties	<installation_location>/conf/cassandra-rackdc.properties
cassandra-topology.properties	/etc/dse/cassandra/cassandra-topology.properties	<installation_location>/conf/cassandra-topology.properties
jmxremote.password	/etc/cassandra/jmxremote.password	<installation_location>/conf/jmxremote.password

Tomcat server configuration file
Configuration file	Installer-Services and package installations	Installer-No Services and tarball installations
server.xml	/etc/dse/resources/tomcat/conf/server.xml	<installation_location>/resources/tomcat/conf/server.xml

Preparing to upgrade from 3.2.5 and later to 4.6.

The DataStax installer upgrades DataStax Enterprise and automatically performs many upgrade tasks.

If you do not use the DataStax installer, follow these steps on each node to prepare to upgrade from DataStax Enterprise 3.2.5 and later to DataStax Enterprise 4.6.

Before upgrading, be sure that each node has adequate free disk space. The required space depends on the compaction strategy. See Disk space.
Verify your current product version. If necessary, upgrade to one these required interim versions before upgrading to 4.6:
- DataStax Enterprise 3.2.5 and later
- DataStax Community or open source Apache Cassandra 1.2.16
Upgrade the SSTables on each node to ensure that all SSTables are on the current version.
```
nodetool upgradesstables
```
This step is required for DataStax Enterprise upgrades that include a major Cassandra version change.

Failure to upgrade SSTables when required results in a significant performance impact and increased disk usage.

If the SSTables are already on the current version, the command returns immediately and no action is taken.
Only for upgrades from 3.2.x: Edit the cassandra.yaml file and remove or comment out the following options:
```
# auth_replication_options:
# replication_factor: 1
```
Only for upgrades from 4.0.0 with Search nodes to 4.5: See Upgrading from DataStax Enterprise 4.0.0 with search nodes.
Verify the Java runtime version and upgrade to the recommended version.
```
java -version
```
The latest version of Oracle Java SE Runtime Environment 7 or 8 or OpenJDK 7 is recommended. The JDK is recommended for development and production systems. The JDK provides useful troubleshooting tools that are not in the JRE, such as jstack, jmap, jps, and jstat.

If using Oracle Java 7, you must use at least 1.7.0_25. If using Oracle Java 8, you must use at least 1.8.0_40.
Familiarize yourself with the changes and features in this release:
- DataStax Enterprise 4.6 release notes.
  
  Endpoint snitch: Starting in DataStax Enterprise 4.6, the endpoint snitch is set in cassandra.yaml, not dse.yaml. The com.datastax.bdp.snitch.DseDelegateSnitch is replaced by com.datastax.bdp.snitch.DseSimpleSnitch in cassandra.yaml and the endpoint_snitch option has been removed from dse.yaml.
  
  The DataStax Installer automatically sets the default endpoint_snitch to DseSimpleSnitch and removes the option from the dse.yaml file.
- General upgrade advice and Apache Cassandra features in NEWS.txt. If you are upgrading from an earlier release, read NEWS.txt all the way back to your current version.
- Apache Cassandra changes in CHANGES.txt.
Back up the configuration files you use to a folder that is not in the directory where you normally run commands. The configuration files are overwritten with default values during installation of the new version.
Run nodetool repair to ensure that data on each replica is consistent with data on other nodes.

Upgrading from 3.2.5 and later to 4.6

The upgrade process for DataStax Enterprise provides minimal downtime (ideally zero). During this process, upgrade and restart one node at a time while other nodes continue to operate online. With a few exceptions, the cluster continues to work as though it were on the earlier version of DataStax Enterprise until all of the nodes in the cluster are upgraded.

Follow these steps on each node to upgrade from DataStax Enterprise 3.2.5 and later to DataStax Enterprise 4.6.

Upgrade order matters. Upgrade nodes in this order:
1. In multiple datacenter clusters, upgrade every node in one datacenter before upgrading another datacenter.
2. Upgrade the seed nodes within a datacenter first.
3. DSE Analytics datacenters
  1. For DSE Analytics nodes using DSE Hadoop, upgrade the Job Tracker node first. Then upgrade Hadoop nodes, followed by Spark nodes.
4. Transactional/DSE Graph datacenters
5. DSE Search datacenters. With a few exceptions, the cluster continues to work as though it were on the earlier version of DataStax Enterprise until all of the nodes in the cluster are upgraded. Upgrade and restart the nodes one at a time. Other nodes in the cluster continue to operate at the earlier version until all nodes are upgraded.
To flush the commit log of the old installation:
```
nodetool -h hostname drain
```
This step saves time when nodes start up after the upgrade, and prevents DSE Search nodes from having to reindex data.

This step is mandatory when upgrading between major Cassandra versions that change SSTable formats, rendering commit logs from the previous version incompatible with the new version.
DSE Analytics nodes: Kill all Spark worker processes.
Stop the node.

Use the appropriate installation type to install the new product version on a supported platform:

RHEL: 4.6, 4.7, 4.8, 5.0
Debian: 4.6, 4.7, 4.8, 5.0
Tarball: 4.6, 4.7, 4.8, 5.0

Install the new product version using the same installation type that is on the system. The upgrade proceeds with installation regardless of the installation type. If you use a different installation type, the upgrade might result in issues.

Open cassandra.yaml to set the endpoint_snitch option to the same snitch that is set in delegated_snitch in dse.yaml:
```
endpoint_snitch: com.datastax.bdp.snitch.DseSimpleSnitch
```
Remove the delegated_snitch option from the old dse.yaml file.
To configure the new version, use your backup configuration files to merge modifications into the configuration files for the new version.
Start the node:
- Installer-Services and Package
- Installer-No Services and Tarball
Verify that the upgraded datacenter names match the datacenter names in the keyspace schema definition:
```
nodetool status
```
Review the logs for warnings, errors, and exceptions. Warnings, errors, and exceptions are frequently found in the logs when starting an upgraded node. Some of these log entries are informational to help you execute specific upgrade-related steps. If you find unexpected warnings, errors, or exceptions, contact DataStax Support.
Repeat the upgrade on each node in the cluster following the recommended order.

When the upgrade includes a major Cassandra version, you must upgrade the SSTables. DataStax recommends upgrading the SSTables on one node at a time or when using racks, one rack at a time.

Failure to upgrade SSTables when required results in a significant performance impact and increased disk usage.

Upgrading is not complete until the SSTables are upgraded.

nodetool upgradesstables

If the SSTables are already on the current version, the command returns immediately and no action is taken. See SSTable compatibility and upgrade version.

Use the --jobs option to set the number of SSTables that upgrade simultaneously. The default setting is 2, which minimizes impact on the cluster. Set to 0 to use all available compaction threads. DataStax recommends running the upgradesstables command on one node at a time, or when using racks, one rack at a time.

You can run the upgradesstables command before all the nodes are upgraded as long as you run this command on only one node at a time, or when using racks, one rack at a time. Running upgradesstables on too many nodes degrades performance.

Upgrading to DataStax Enterprise 4.6

Apache Cassandra® version change

General recommendations

Upgrade restrictions and limitations

DataStax Enterprise and Apache Cassandra configuration files

Preparing to upgrade from 3.2.5 and later to 4.6.

Upgrading from 3.2.5 and later to 4.6

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