Index: kernel-impl/src/main/java/org/sakaiproject/event/impl/ClusterEventTracking.java
===================================================================
--- kernel-impl/src/main/java/org/sakaiproject/event/impl/ClusterEventTracking.java	(revision 81984)
+++ kernel-impl/src/main/java/org/sakaiproject/event/impl/ClusterEventTracking.java	(working copy)
@@ -49,7 +49,16 @@
  */
 public abstract class ClusterEventTracking extends BaseEventTrackingService implements Runnable
 {
-	/** Our logger. */
+
+    // see http://jira.sakaiproject.org/browse/SAK-3793 for more info about these numbers
+    private static final long WARNING_SAFE_EVENTS_TABLE_SIZE = 18000000l;
+    private static final long MAX_SAFE_EVENTS_TABLE_SIZE = 20000000l;
+
+    private static final long WARNING_SAFE_SESSIONS_TABLE_SIZE = 1750000l;
+    private static final long MAX_SAFE_SESSIONS_TABLE_SIZE = 2000000l;
+
+
+    /** Our logger. */
 	private static Log M_log = LogFactory.getLog(ClusterEventTracking.class);
 
 	/** String used to identify this service in the logs */
@@ -64,6 +73,10 @@
 	/** Last event code read from the db */
 	protected long m_lastEventSeq = 0;
 
+    protected long m_totalEventsCount = 0;
+
+    protected long m_totalSessionsCount = 0;
+
 	/** Queue of events to write if we are batching. */
 	protected Collection m_eventQueue = null;
 
@@ -208,6 +221,34 @@
 				start();
 			}
 
+            // do the check for event oversizing and output log warning if needed - SAK-3793
+			long totalEventsCount = getEventsCount();
+            if (totalEventsCount > WARNING_SAFE_EVENTS_TABLE_SIZE) {
+                M_log.info("The SAKAI_EVENT table size ("+totalEventsCount+") is approaching the point at which " +
+                		"performance will begin to degrade ("+MAX_SAFE_EVENTS_TABLE_SIZE+
+                		"), we recommend you archive older events over to another table, " +
+                		"remove older rows, or truncate this table before it reaches a size of "+MAX_SAFE_EVENTS_TABLE_SIZE);
+            } else if (totalEventsCount > MAX_SAFE_EVENTS_TABLE_SIZE) {
+                M_log.warn("The SAKAI_EVENT table size ("+totalEventsCount+") has passed the point at which " +
+                        "performance will begin to degrade ("+MAX_SAFE_EVENTS_TABLE_SIZE+
+                        "), we recommend you archive older events over to another table, " +
+                        "remove older rows, or truncate this table to ensure that performance is not affected negatively");
+			}
+
+            long totalSessionsCount = getSessionsCount();
+            if (totalSessionsCount > WARNING_SAFE_SESSIONS_TABLE_SIZE) {
+                M_log.info("The SAKAI_SESSIONS table size ("+totalSessionsCount+") is approaching the point at which " +
+                        "performance will begin to degrade ("+MAX_SAFE_SESSIONS_TABLE_SIZE+
+                        "), we recommend you archive older sessions over to another table, " +
+                        "remove older rows, or truncate this table before it reaches a size of "+MAX_SAFE_SESSIONS_TABLE_SIZE);
+            } else if (totalSessionsCount > MAX_SAFE_SESSIONS_TABLE_SIZE) {
+                M_log.warn("The SAKAI_SESSIONS table size ("+totalSessionsCount+") has passed the point at which " +
+                        "performance will begin to degrade ("+MAX_SAFE_SESSIONS_TABLE_SIZE+
+                        "), we recommend you archive older events over to another table, " +
+                        "remove older rows, or truncate this table to ensure that performance is not affected negatively");
+            }
+            // end SAK-3793
+
 			M_log.info(this + ".init() - period: " + m_period / 1000 + " batch: " + m_batchWrite + " checkDb: " + m_checkDb);
 
 			this.post(this.newEvent("server.start", serverConfigurationService().getString("version.sakai", "unknown") + "/" + serverConfigurationService().getString("version.service", "unknown"), false));
@@ -219,6 +260,52 @@
 		}
 	}
 
+    /**
+     * @return the current total number of events in the events table (data storage)
+     */
+    protected long getEventsCount() {
+        /*
+         * NOTE: this is a weird way to get the value out but it matches the existing code
+         * added for SAK-3793
+         */
+        m_totalEventsCount = 0;
+        final String eventCountStmt = clusterEventTrackingServiceSql.getEventsCountSql();
+        sqlService().dbRead(eventCountStmt, null, new SqlReader() {
+            public Object readSqlResultRecord(ResultSet result) {
+                try {
+                    m_totalEventsCount = result.getLong(1);
+                } catch (SQLException ignore) {
+                    M_log.warn("Could not get count of events table using SQL: " + eventCountStmt);
+                }
+                return new Long(m_totalEventsCount);
+            }
+        });
+        return m_totalEventsCount;
+    }
+
+    /**
+     * @return the current total number of sessions in the sessions table (data storage)
+     */
+    protected long getSessionsCount() {
+        /*
+         * NOTE: this is a weird way to get the value out but it matches the existing code
+         * added for SAK-3793
+         */
+        m_totalSessionsCount = 0;
+        final String sessionCountStmt = clusterEventTrackingServiceSql.getSessionsCountSql();
+        sqlService().dbRead(sessionCountStmt, null, new SqlReader() {
+            public Object readSqlResultRecord(ResultSet result) {
+                try {
+                    m_totalSessionsCount = result.getLong(1);
+                } catch (SQLException ignore) {
+                    M_log.warn("Could not get count of sessions table using SQL: " + sessionCountStmt);
+                }
+                return new Long(m_totalSessionsCount);
+            }
+        });
+        return m_totalSessionsCount;
+    }
+
 	/**
 	 * Final cleanup.
 	 */
Index: kernel-impl/src/main/java/org/sakaiproject/event/impl/ClusterEventTrackingServiceSql.java
===================================================================
--- kernel-impl/src/main/java/org/sakaiproject/event/impl/ClusterEventTrackingServiceSql.java	(revision 81984)
+++ kernel-impl/src/main/java/org/sakaiproject/event/impl/ClusterEventTrackingServiceSql.java	(working copy)
@@ -40,4 +40,15 @@
 	 * returns the sql statement which retrieves the largest event id from the sakai_event table.
 	 */
 	String getMaxEventIdSql();
+
+    /**
+     * returns the sql statement which counts the number of events in the event table
+     */
+    String getEventsCountSql();
+
+    /**
+     * returns the sql statement which counts the number of sessions in the sessions table
+     */
+    String getSessionsCountSql();
+
 }
Index: kernel-impl/src/main/java/org/sakaiproject/event/impl/ClusterEventTrackingServiceSqlDefault.java
===================================================================
--- kernel-impl/src/main/java/org/sakaiproject/event/impl/ClusterEventTrackingServiceSqlDefault.java	(revision 81984)
+++ kernel-impl/src/main/java/org/sakaiproject/event/impl/ClusterEventTrackingServiceSqlDefault.java	(working copy)
@@ -20,9 +20,6 @@
  **********************************************************************************/
 package org.sakaiproject.event.impl;
 
-import org.apache.commons.logging.Log;
-import org.apache.commons.logging.LogFactory;
-
 /**
  * methods for accessing cluster event tracking data in a database.
  */
@@ -59,4 +56,19 @@
 	{
 		return "select MAX(EVENT_ID) from SAKAI_EVENT";
 	}
+
+    /* (non-Javadoc)
+     * @see org.sakaiproject.event.impl.ClusterEventTrackingServiceSql#getEventsCountSql()
+     */
+    public String getEventsCountSql() {
+        return "select COUNT(*) from SAKAI_EVENT";
+    }
+
+    /* (non-Javadoc)
+     * @see org.sakaiproject.event.impl.ClusterEventTrackingServiceSql#getSessionsCountSql()
+     */
+    public String getSessionsCountSql() {
+        return "select COUNT(*) from SAKAI_SESSION";
+    }
+
 }