private static String getPurgeStatement(DatabaseType type)
	{
        return switch (type) {
            case postgresql -> PURGE_FOR_SIZE_POSTGRESQL;
            case mysql      -> PURGE_FOR_SIZE_MYSQL;
            case hsqldb     -> PURGE_FOR_SIZE_HSQLDB;
            case oracle     -> PURGE_FOR_SIZE_ORACLE;
            case sqlserver  -> PURGE_FOR_SIZE_SQLSERVER;
            default         -> PURGE_FOR_SIZE;
        };
	}
Purges all items from the database that exceed the defined item count on
all nodes.
xmppserver/src/main/java/org/jivesoftware/openfire/pubsub/DefaultPubSubPersistenceProvider.java