On start-up, a server that is a member of a cluster must verify that it is “in sync” with other cluster members by checking its cluster version number against other servers in the cluster. A server that is not in-sync remains in admin mode and does not join the cluster. The com.sybase.jaguar.cluster.startup cluster property specifies the testing algorithm. Set or modify this property from the Advanced tab in the Cluster Properties window—see com.sybase.jaguar.cluster.startup.
The com.sybase.jaguar.cluster.startup values and corresponding algorithms are:
check_primary (default value) – With this setting, each server tests its cluster version number against the primary before joining the cluster, using the following algorithm:
If any other cluster member (including the primary) is reachable and has a higher cluster version number, this server moves to Admin mode since it is not “in sync.”
If the primary is available and has the same cluster version number, this server joins the cluster and is ready to accept client connections.
If the primary is available and has a different cluster version number, this server moves to Admin mode since it is not “in sync.”
If none of the above conditions are met, the server waits briefly, then returns to the first step in this algorithm.
check_servers – With this setting, each server tests its cluster version number against the other member servers before joining the cluster, using this algorithm:
If any other cluster member (including the primary) is reachable and has a higher cluster version number, this server moves to Admin mode since it is not “in sync.”
Let M be the number of cluster members (including the primary), and let N equal M/2 (integer division). If at least N other servers are available and have the same cluster version number, this server joins the cluster and is ready to accept client connections.
If none of the above conditions are met, the server waits briefly then returns to the first step in this algorithm.
The check_servers option allows a server to join a cluster even if the primary is not available. This prevents a single point of failure if the primary server becomes unavailable.
disable_check – no checking is performed. For a cluster with only two servers (including the primary), use this option and manually verify that the secondary server is “in sync.” For a cluster with three or more servers, Sybase discourages the use of this option, since it can result in “out-of-sync” cluster members running together.
A server in Admin mode can be put into Ready mode as described in “Switching to Ready mode”. If a server is in Admin mode due to a cluster version number mismatch, then using Set Ready is the manual equivalent of disable_check, so using Set Ready in this case is also discouraged as it may result in “out-of-sync” cluster members running together. Sybase recommends that you synchronize the cluster instead. See “Synchronizing a cluster from EAServer Manager” for more information.
| Copyright © 2005. Sybase Inc. All rights reserved. |
|
|
