This document summarizes Diego Pacheco's presentation on Cassandra. It covers the Cassandra write path, tombstones, compaction strategies, row and bloom filters, SASI indexes, materialized views, counter families, and anti-patterns. It also discusses Cassandra's implementation at Uber using Mesos. The presentation addresses how data is written to disk in immutable SSTables and compacted over time to remove tombstones, and different compaction strategies for various workloads. It explains techniques like row caching, bloom filters, secondary indexes, materialized views and counters.

1. Cassandra
part 2
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Diego Pacheco

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3. Agenda
❏ RE-CAP
❏ Cassandra Write Path
❏ Tombstones
❏ Compaction Strategies
❏ Row Cache
❏ Bloom Filter
❏ SASI Index
❏ Materialized Views
❏ Counter Families
❏ Anti-Patterns
❏ Cassandra running at UBER in MESOS use case
❏ Q&A

4. http://cassandra.apache.org/

5. RE-CAP: Partition Strategy

6. Cassandra Write Path
❏ SSTable => Sorted Array of Strings.
❏ Write to Disk: Merges and Pre-sorts
happens.
❏ SSTables are IMMUTABLE.
❏ Compaction happens:
❏ Time to time
❏ Prune deleted data
❏ Has thread-offs

7. Tombstones
❏ Deleted data is MARKED as Removed == Tombstone
❏ Data is deleted and removed during compaction
❏ Compaction can happen in few days depending of the
configs.
❏ Queries on partition with lots of tombstones requires lots of
filtering which can slow down the CASS performance.
❏ Collections operations can lead to tombstones depending
on what you do.
❏ There are Compaction Trade-Offs.

8. Compaction Strategies
❏ STCS
❏ Default
❏ Insert-Heavy
❏ General Workloads
❏ LCS
❏ Read Heavy
❏ More Updates than
Inserts
❏ DTCS
❏ Time Series
❏ Inserts out of order
❏ Updates for old data

9. Cassandra ROW CACHE
❏ Buffer FULL merged row into memory
❏ Increase a lot the throughput
❏ Row Cache works with Key Cache
❏ Key Cache = Where the partition is on DISK.
CREATE TABLE status (
user text,
status_id timeuuid,
status text,
PRIMARY KEY (user, status_id))
WITH CLUSTERING ORDER BY (status_id DESC)
AND caching = '{"keys":"ALL", "rows_per_partition":"10"}'

10. Cassandra Bloom Filter
❏ Bloom Filter: Technique created on the 70s to filter db matches.
❏ Space Efficient
❏ Probabilistic Data Structures
❏ For each SSTable there is a Bloom Filter
❏ Used for Index scans - not used to range scans
❏ Stored OFF HEAP
❏ Tunable per TABLE
❏ Cassandra uses bloom filters to know if the data is on the ROW or not.

11. Cassandra READ Path

12. SASI
❏ Secondary Index: Not the primary key.
❏ Lookup tables: bySomething
❏ Distributed Index
❏ Search Like Capabilities: %diego%
❏ Great when:
❏ Multi fields Search
❏ You know the partition key
❏ Indexing static columns
❏ Issues:
❏ More than 1000 rows returned
❏ Searching in Large Partitions
❏ Aggressive Read SLOs
❏ Search for Analytics(Use Spark/Flink)
❏ Ordering Search is important

13. SASI
Samples
❏ SELECT * FROM users WHERE firstname LIKE 'Die%';
❏ SELECT * FROM users WHERE lastname LIKE '%ie%';
❏ SELECT * FROM users WHERE
created_date > '2015-01-02' AND created_date < '2017-01-02';

14. Materialized Views
❏ Automated - Table managed for you, Denormalization
❏ Copies of the data in different partitions / replicas
❏ Some Write penalty but acceptable performance
❏ Store results in table which can be indexed
❏ Update ASYNC
❏ Great For:
❏ Caching
❏ Result Sets
❏ Dashbaords
SAMPLE
CREATE MATERIALIZED VIEW all_time_high AS
SELECT user FROM scores WHERE
game IS NOT NULL AND
score IS NOT NULL
PRIMARY KEY (game,score) WITH CLUSTERING ORDER BY (score DESC)

15. Cassandra Counter Family
❏ Static VS Dynamic Column families
❏ Dynamic Column families A.K.A Wide Rows
❏ Wide Rows is good for: Ordering,Grouping and Filtering.
❏ Wide Rows are not split into NODES.
❏ Counters Internally:
❏ Calculated and sum of all replicas
❏ Split into fragments called SHARDs.
❏ Logical clock monotonically increased
❏ 3 tuple = { NODE_COUNTER_ID, SHARD_LOGICAL_CLOCK, SHARD_VALUE }

16. Anti-Patterns
❏ Using Cassandra as a queue or queue-like table
❏ Tombstones
❏ Lots of deleted columns(expiry) and slice-queries don't play well
❏ http://www.datastax.com/dev/blog/cassandra-anti-patterns-queues-and-queue-like-datasets
❏ CQL Nulls
❏ Reading Tombstones
❏ Write NULL create tombstones
❏ Intensive Updates on SAME column
❏ Sensor table (ID,VALUE)
❏ Physical Limits
❏ Solution: Timestamp as cluster key.

17. Cassandra at UBER using MESOS (2016 data)

18. Cassandra
part 2
diegopacheco
@diego_pacheco
Diego Pacheco