KnowledgeBase/CII.md

@@ -85,6 +85,52 @@ Most demo apps require CII Services be running on your host or on another host =
 ### ------------------------------------------------
 --------------------------------------------------------------------------
 
+### Cannot create Datapoints [OLDB]
+
+**Problem**
+
+Trying to create a datapoint, you get this error:
+```
+   Cannot save to zpb.rr://ciiconfservicehost:9116/configuration/service/clientApi
+```
+
+resp. you get this error:
+```
+[ERROR][CiiOldb] Unknown error occurred ::elt::error::icd::CiiSerializableException
+```	
+and in the IntCfg-logs (as root: journalctl -u srv-config) you see:
+```	
+Cannot save to zpb.rr://ciiconfservicehost:9116/configuration/service/clientApi
+```
+
+This can be caused by low disk space (< 5%) available for the oldb permanent store:
+```
+df -h /var/lib/elasticsearch
+```
+
+**Solution**
+
+```
+# Remove old log files:
+	find /var/log/elasticsearch -type f -mtime +30 -delete
+
+# Put database back into read-write mode:
+	curl -XPUT -H "Content-Type: application/json" localhost:9200/_all/_settings -d '
+	{ "index.blocks.read_only_allow_delete": null }'
+
+# Remove old log records:
+	curl -X POST "localhost:9200/cii_log_default_index/_delete_by_query?pretty" -H 'Content-Type: application/json' -d'
+	{ "query": { "range" : { "@timestamp" : { "lte": "now-30d/d" } } } }'
+```
+
+**Background**
+
+If disk usage is above 95%, elasticsearch goes into read-only mode, and creating new datapoints is not possible any more. To remove old content from the database, it is first necessary to create some free space on the disk (since the database needs space to perform deletetion-operations), then unlock the database, and then remove unnecessary old content from it.
+
+
+--------------------------------------------------------------------------
+--------------------------------------------------------------------------
+--------------------------------------------------------------------------
 ### Insufficent Manuals, Contributions
 
 **Problem**