Data present despite SSTable deletion - cassandra

Question

I'm working on a single Cassandra 3.11.2 node(RHEL 6.5). In keyspace(named 'test'), I've a table named 'test'. I entered some rows via cqlsh and then did nodetool flush. I checked in the data directory to confirm that a SSTable got created. Now I deleted all the .db files(from the test.test data directory using rm *.db).
Strangely, I can still see all the rows in cqlsh! I don't understand, how this is happening since I manually deleted the SSTable.
Given below is my keyspace:
CREATE KEYSPACE test WITH replication = {'class': 'SimpleStrategy', 'replication_factor': '1'} AND durable_writes = true;
Given below is the table:
CREATE TABLE test.test (
aadhar_number int PRIMARY KEY,
address text,
name text
) WITH bloom_filter_fp_chance = 0.01
AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
AND comment = ''
AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'max_threshold': '32', 'min_threshold': '4'}
AND compression = {'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.LZ4Compressor'}
AND crc_check_chance = 1.0
AND dclocal_read_repair_chance = 0.1
AND default_time_to_live = 0
AND gc_grace_seconds = 864000
AND max_index_interval = 2048
AND memtable_flush_period_in_ms = 0
AND min_index_interval = 128
AND read_repair_chance = 0.0
AND speculative_retry = '99PERCENTILE';
Given below is the output of nodetool tablestats command(after I had deleted the SSTable):
Keyspace : test
Read Count: 0
Read Latency: NaN ms
Write Count: 13
Write Latency: 0.11269230769230769 ms
Pending Flushes: 0
Table: test
SSTable count: 1
Space used (live): 5220
Space used (total): 5220
Space used by snapshots (total): 0
Off heap memory used (total): 48
SSTable Compression Ratio: 0.7974683544303798
Number of partitions (estimate): 255
Memtable cell count: 0
Memtable data size: 0
Memtable off heap memory used: 0
Memtable switch count: 4
Local read count: 0
Local read latency: NaN ms
Local write count: 10
Local write latency: NaN ms
Pending flushes: 0
Percent repaired: 0.0
Bloom filter false positives: 0
Bloom filter false ratio: 0.00000
Bloom filter space used: 24
Bloom filter off heap memory used: 16
Index summary off heap memory used: 16
Compression metadata off heap memory used: 16
Compacted partition minimum bytes: 18
Compacted partition maximum bytes: 50
Compacted partition mean bytes: 36
Average live cells per slice (last five minutes): 5.0
Maximum live cells per slice (last five minutes): 5
Average tombstones per slice (last five minutes): 1.0
Maximum tombstones per slice (last five minutes): 1
Dropped Mutations: 0
I restarted Cassandra and only then the data stopped showing in cqlsh.
A very good article for understanding filesystem details in linux.

Answer 1

On linux, filenames are just pointers (inodes) that point to the memory where the file resides. When Cassandra open the files, it holds a link to it. When you use rm to remove the file, you delete the link from the filesystem to the physical memory, but the file is still referenced by a live process and is therefore not deleted. You can easily check that with the command lsof (list open files). There is a flag to list for a given pid (check the cassandra pid with something like ps aux | grep cassandra)
Obviously, when you restart Cassandra, the file get deleted.