Core group protocol versions

Core group members interact with each other through a variety of protocols such as the discovery protocol, the failure detection protocol, and the view synchrony protocol. Each of these protocols define a set of formatted messages that core group members exchange according to a common algorithm.

Tip: This topic references one or more of the application server log files. As a recommended alternative, you can configure the server to use the High Performance Extensible Logging (HPEL) log and trace infrastructure instead of using SystemOut.log , SystemErr.log, trace.log, and activity.log files on distributed and IBM® i systems. You can also use HPEL in conjunction with your native z/OS® logging facilities. If you are using HPEL, you can access all of your log and trace information using the LogViewer command-line tool from your server profile bin directory. See the information about using HPEL to troubleshoot applications for more information on using HPEL.

New protocol versions are added to the product if new messages, or new algorithms are required to support new product features, or to improve core group performance. Because the new messages, or new algorithm might not be compatible with the existing messages or algorithm, a new protocol might not be able to interoperate with the old version of the protocol.

There are two major categories or groups of protocols.

A collection of lower-level protocols, which are also referred to as the lower-level wire format protocols. These protocols are used by the DCS layer. The setting for the IBM_CS_WIRE_FORMAT_VERSION core group custom property determines which protocol version is used for this group of protocols.
Whenever the value specified for this property changes, an HMGR0226I message, similar to the following example, is sent to the SystemOut.log file, or, for the z/OS platform, to either SYSOUT or SYSPRINT:
```
HMGR0226I: The core stack configuration parameter IBM_CS_WIRE_FORMAT_VERSION has been set to 6.1.0.
```
A collection of higher level protocols, which are also referred to as the high availability manager protocols. These protocols are used by the high availability manager layer. The setting for the IBM_CS_HAM_PROTOCOL_VERSION core group custom property determines which protocol version is used for this group of protocols.
Whenever the value specified for this property changes, a HMGR0226I message, similar to the following message, is sent to the SystemOut.log file, or, for the z/OS platform, to either SYSOUT or SYSPRINT:
```
HMGR0226I: The core stack configuration parameter IBM_CS_HAM_PROTOCOL_VERSION 
   has been set to 6.0.2.31.
```
This message indicates that the high availability manager protocol version 6.0.2.31 is being used.

The protocol version settings for each of these two categories are independent of each other.

Whenever a new protocol version is added to the product:

The new protocol version is assigned a unique ID.
Support for the existing, in-service protocol versions is retained because all of the members of a core group might not be running at the same product level.
The oldest supported protocol version is the default protocol version. Older protocol versions are deprecated using the standard product deprecation rules.
You must explicitly update the IBM_CS_WIRE_FORMAT_VERSION and the IBM_CS_HAM_PROTOCOL_VERSION core group custom property to change the DCS protocol version and the High Availability Manager protocol version respectively.
Avoid trouble: You cannot update to a newer protocol version until all of the members of this core group are upgraded to a code level that supports the newer protocol version.

When to select a new core group protocol version

Core group protocol versions are always cumulative. Any functional enhancement that is provided in a previous protocol, is included in any subsequent protocols. It is recommended that you always use the latest protocol version whenever possible. But, before configuring the members of a core group to use a new protocol version, you must make sure that all of the core group members are running at a WebSphere® Application Server code level (VRM) that is equal to or greater than the new protocol version.

When you have determined that you can use newer core group protocol versions with a particular core group, use the IBM_CS_WIRE_FORMAT_VERSION and the IBM_CS_HAM_PROTOCOL_VERSION core group custom properties to upgrade the DCS layer protocols and the High Availability Manager layer protocols respectively. All core group members will be configured to run with that newer version.

Avoid trouble: You do not have to restart the core group members when you move from an older protocol version to a newer protocol version. However, you must restart all of the core group members if you move from a newer protocol version to an older protocol version.

Using the high availability manager protocol to establish transparent bridge failover support

Core group bridges provide the mechanism that is used to represent and manage the cross core group state that is used by WebSphere Application Server components. Part of the management process for this cross-core group state is to perform core group bridge state rebuilds whenever there is a change in the number of running core group bridges in a topology. The core group bridge state rebuild is the means by which core group bridges calculate the ownership, and distribution of the cross-core group state among the running set of bridges.

During core group bridge state rebuilds, cross-core group state can be moved between running bridges. This situation might cause the data to be temporarily unavailable until the bridge has completed the rebuild process. Common symptoms of this problem include:

JNDI lookups failing.
A WebSphere proxy server, or on-demand router generates a 503 response code after a core group bridge failover occurs

The following array index out-of-bounds exception occurs:

[7/9/08 17:12:20:749 EDT] 00000030 UserCallbacks E 
HMGR0142E: An error occurred in a component called back by the High Availability Manager 
The exception is java.lang.ArrayIndexOutOfBoundsException at
com.ibm.ws.cluster.propagation.bulletinboard.BBDescriptionManager.getOrderedBytes(BBDescriptionManager.java:618)

Best practice: If you are running on Version 7.0.0.1 or later, set the IBM_CS_HAM_PROTOCOL_VERSION core group custom property to 6.0.2.31 for all of your core groups to avoid a possible high availability state outage during core group bridge failover. When this custom property is set to 6.0.2.31, the remaining bridges recover the high availability state of the failed bridge without the data being unavailable in the local core group.

Avoid trouble:

Ensure that all core groups that are connected with core group bridges are running the same protocol version.
Transparent bridge failover is designed to hold state data constant during core group bridge rebuilds along the state data path, which is the path that consists of the state provider, one core group bridge in each respective core group, and a state data consumer. Failure scenarios involving core groups with no remaining active bridges might still result in temporary state outages.

Determining which protocol version to use

Best practice: Use the newest protocol version whenever possible. This practice is especially critical for large topologies because most of the recent protocol changes include scalability improvements. However, before configuring the members of a core group to use a new protocol version, you must verify that all of the core group members are running at a product code level (VRM) that is equal to or greater than the VRM in which the desired protocol version was added to the product. For example:

A core group that contains core group members at any supported VRM can be configured to use the Version 6.0.0, 6.0.2.9, or 6.1.0 wire format protocol.
A core group that contains a mix of Version 6.1.0.19 and 7.0.0.1 core group members can be configured to use the Version 6.0.2.31 high availability manager protocol.

Supported core group protocol version IDs

The following tables summarize for each protocol category the minimum level of the product that core group members must be running at before they can be associated with a specific protocol version. These tables also describe the new capabilities that were added in each protocol version.

Use these tables to determine which protocol versions you can use with a particular core group, and then use either the IBM_CS_WIRE_FORMAT_VERSION or the IBM_CS_HAM_PROTOCOL_VERSION core group custom property to configure all of the members of that core group to run using the newest of those protocol versions that are supported by the level of the product on which you are running. The high availability manager automatically detects the configuration changes and starts to use the new core group protocol version with these core group members.

Deprecated feature: Wire format protocol versions 6.0.0 and 6.0.2.9 are deprecated. Whenever possible you should use a newer protocol version.

Table 1. Supported wire format protocol version IDs . The protocol version ID indicates the first version, release, and modification level in which that version is included. The following table lists the supported wire format protocol version IDs.
Version ID	Required Minimum product Level	Description
6.0.0	Any	This protocol version is the original or base version. All versions of the high availability manager can use this protocol. If you do not specify a particular wire format protocol version, the high availability manager uses this version.
6.0.2.9	Any supported version	This protocol version facilitates core group bridge scalability. This version is recommended for large topologies that contain multiple core groups and core group bridges as part of their configuration.
6.1.0	Any supported version	This version adds core group scalability improvements, and more support for large topologies.

Table 2. Supported high availability manager protocol version IDs . The protocol version ID indicates the first version, release, and modification level in which that version is included. The following table lists the supported high availability manager protocol version IDs.
Version ID	Required Minimum product Level	Description
6.0.2.31	6.1.0.19 for Version 6.1, 7.0.0.1 for Version 7.0, and the initial release of any later versions of the product	This protocol version is the original or base version of the high availability manager protocol, and is available in any supported version of the product to facilitate core group bridge scalability. This protocol version is recommended for topologies that contain multiple core groups and core group bridges as part of their configuration. You must specify the high availability manager protocol version for the high availability manager to use the protocol. There is no default version.