Cassandra

Tags: Databases, distributed systems

Internals

• Seed nodes:
  • No purpose other than bootstrapping the gossip process
  • DO NOT MAKE ALL NODES SEED NODES

concurrent_compactors

• Sets the number of IO threads dedicated to compaction
• If too high, can cause IO starvation and not servicing requests
  • Depends on NVME drives
• set by the concurrenct_compactors string in yaml
  • can also use nodetool setconcurrent_compactors in C* > 3

Counter Table TTL’s

• https://issues.apache.org/jira/browse/CASSANDRA-2103
• https://blog.knoldus.com/cassandra-counter-column-and-table/
• https://docs.scylladb.com/using-scylla/counters/
• https://docs.scylladb.com/getting-started/time_to_live/
• https://stackoverflow.com/questions/29564744/data-modeling-with-counters-in-cassandra-expiring-columns
• https://github.com/Netflix/astyanax/wiki/Working-with-counter-columns
• https://dzone.com/articles/cassandra-counter-columns-and-tables
• https://stackoverflow.com/questions/24881957/what-is-the-way-for-counting-number-of-columns-in-row-in-cassandra
• https://www.ably.io/blog/cassandra-counter-columns-nice-in-theory-hazardous-in-practice

Jolokia Agent

• https://stackoverflow.com/questions/35318593/jolokia-agent-for-cassandra
• https://stackoverflow.com/questions/35318593/jolokia-agent-for-cassandra

CQLSH

• cqlsh specifically checks for python2.7, which may need to be aliased somewhere

Scylla

• Xandra driver uses https://queue.acm.org/appendices/codel.html
• Whether tweaking tombstone_compaction_interval affects things: https://github.com/PaytmLabs/cassandra/blob/master/src/java/org/apache/cassandra/db/compaction/AbstractCompactionStrategy.java#L360

Tracing

• https://opensource.docs.scylladb.com/stable/using-scylla/tracing.html#probabilistic-tracing

• normally you can turn on CQL tracing with

  cqlsh> TRACING ON

• also can set nodetool settraceprobability 0.0001

Cassandra Gossiper Protocol

• Gossiper chooses a random node in the cluster and initializes a session with it
  • each gossip require 3 messages
• Sends its friend a Gossip Disget Syn Message
• Followed by a GossipDigestAck message
• Th eoriginal ack is returned with a gossip digestack2 message

Talks

• https://github.com/ngcc/ngcc2019/tree/master