I have noticed in the cassandra system.log that there is some issue with sstable metadata, the messages says:
WARN [Thread-6] 2018-07-25 07:12:47,928 SSTableReader.java:249 - Reading cardinality from Statistics.db failed for /opt/data/disk5/data/keyspace/table/mc-big-Data.db
Although there is no such file. The message has appeared after i've changed the compaction strategy from SizeTiered to Leveled.
Currently i'm running nodetool scrub to rebuilt the sstable, and it takes a lot of time to scrub all sstables.
Reading the code it is said that if this metada is broken, then estimating the keys will be done using index summary. How expensive it is ?https://github.com/apache/cassandra/blob/cassandra-3.0.15/src/java/org/apache/cassandra/io/sstable/format/SSTableReader.java#L245
The main question is why has this happened?