We are working on Appian 7.9 version and facing this issue after checking for “D

It does look like the root cause of the issue was that the search-server was not running.

For future reference, you can review the search_serve_cluster.csv from <APPIAN_HOME>\\logs\\data-metrics to check the status of the search-server.

Based on the log file you attached, the search_serve_cluster.csv indicated that the search server was not running.
Timestamp          Cluster Name          Status          Timed Out          Number of Nodes          Number of Data Nodes          Active Primary Shards          Active Shards          Relocating Shards          Initializing Shards          Unassigned Shards
9 Jun 2015 17:28:50 GMT          n/a          None of the configured nodes are available: []          FALSE          0          0          0          0          0          0          0
9 Jun 2015 17:33:50 GMT          n/a          None of the configured nodes are available: []          FALSE          0          0          0          0          0          0          0
9 Jun 2015 17:38:50 GMT          n/a          None of the configured nodes are available: []          FALSE          0          0          0          0          0          0          0

Additional information can be found here:
forum.appian.com/.../Logging.html

It does look like the root cause of the issue was that the search-server was not running.

For future reference, you can review the search_serve_cluster.csv from <APPIAN_HOME>\\logs\\data-metrics to check the status of the search-server.

Based on the log file you attached, the search_serve_cluster.csv indicated that the search server was not running.
Timestamp          Cluster Name          Status          Timed Out          Number of Nodes          Number of Data Nodes          Active Primary Shards          Active Shards          Relocating Shards          Initializing Shards          Unassigned Shards
9 Jun 2015 17:28:50 GMT          n/a          None of the configured nodes are available: []          FALSE          0          0          0          0          0          0          0
9 Jun 2015 17:33:50 GMT          n/a          None of the configured nodes are available: []          FALSE          0          0          0          0          0          0          0
9 Jun 2015 17:38:50 GMT          n/a          None of the configured nodes are available: []          FALSE          0          0          0          0          0          0          0

Additional information can be found here:
forum.appian.com/.../Logging.html