[CASSANDRA-8646] Row Cache Miss with clustering key

• Type: Improvement
• Status: Open
• Priority: Low
• Resolution: Unresolved
• Fix Version/s: 2.1.x

Environment

OS: CentOS 6.5, [cqlsh 5.0.1 | Cassandra 2.1.2 | CQL spec 3.2.0 | Native protocol v3]. Using CQL CLI for query analysis.

• Assignee: Unassigned
• Reporter: Nitin Padalia
• Created: 20/Jan/15 07:14
• Updated: 16/Apr/19 09:31

Description

Cassandra doesn't hit row cache for first and last row of a partition if we mention cluster keys in where condition. However if we use limit then it hits the row cache for the same rows.

E.G. I've a column family:
CREATE TABLE ucxndirdb2.usertable_cache (
user_id uuid,
dept_id uuid,
location_id text,
locationmap_id uuid,
PRIMARY KEY ((user_id, dept_id), location_id)
) WITH CLUSTERING ORDER BY (location_id ASC)
AND bloom_filter_fp_chance = 0.01
AND caching = '

{"keys":"ALL", "rows_per_partition":"3"}

'
AND comment = ''
AND compaction =

{'min_threshold': '4', 'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'max_threshold': '32'}

AND compression =

{'sstable_compression': 'org.apache.cassandra.io.compress.LZ4Compressor'}

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 = '99.0PERCENTILE';

It has 3 rows per partition keys enabled for row cache.

Now for a cached request, if I run:
select * from usertable_cache WHERE user_id = 7bf16edf-b552-40f4-94ac-87b2e878d8c2 and dept_id = de3ac44f-2078-4321-a47c-de96c615d40d limit 3;

Then its a cache hit with follow results:
user_id | dept_id | location_id | locationmap_id
------------------------------------------------------------------------------------+-------------------------------------
7bf16edf-b552-40f4-94ac-87b2e878d8c2 | de3ac44f-2078-4321-a47c-de96c615d40d | ABC4:1 | 32b97639-ea5b-427f-8c27-8a5016e2ad6e
7bf16edf-b552-40f4-94ac-87b2e878d8c2 | de3ac44f-2078-4321-a47c-de96c615d40d | ABC4:10 | dfacc9fc-7a6a-4fb4-8a4f-c13c606d552b
7bf16edf-b552-40f4-94ac-87b2e878d8c2 | de3ac44f-2078-4321-a47c-de96c615d40d | ABC4:100 | 9ba7236a-6124-41c8-839b-edd299f510f7

However If I run:
select * from usertable_cache WHERE user_id = 7bf16edf-b552-40f4-94ac-87b2e878d8c2 and dept_id = de3ac44f-2078-4321-a47c-de96c615d40d and location_id = 'ABC4:1';
or
select * from usertable_cache WHERE user_id = 7bf16edf-b552-40f4-94ac-87b2e878d8c2 and dept_id = de3ac44f-2078-4321-a47c-de96c615d40d and location_id = 'ABC4:100';

Then its a cache miss. However for following its hit for following
select * from usertable_cache WHERE user_id = 7bf16edf-b552-40f4-94ac-87b2e878d8c2 and dept_id = de3ac44f-2078-4321-a47c-de96c615d40d and location_id = 'ABC4:10';

and this behavior is consistent by increasing/decreasing rows_per_partiton setting. Cache is miss for only first and last record of the partition.