Hi,
We are trying to Decouple our Reporting DB from OLTP. Need urgent help on the
feasibility of proposed solution for PRODUCTION.
Use Case: Currently, our OLTP and Reporting application and DB are same. Some
CF are used for both OLTP and Reporting while others are solely used for
Reporting.Every business transaction synchronously updates the main OLTP CF and
asynchronously updates other Reporting CFs.
Problem Statement:
1. Decouple Reporting and OLTP such that Reporting load can't impact OLTP
performance.
2. Scaling of Reporting and OLTP modules must be independent
3. OLTP client should not update all Reporting CFs. We generate Data Records on
File sytem/shared disk.Reporting should use these Records to create Reporting
DB.
4. Small customers may do OLTP and Reporting on same 3-node cluster. Bigger
customers can be given an option to have dedicated OLTP and Reporting nodes.
So, standard Hardware box should be usable for 3 deployments (OLTP,Reporting or
OLTP+Reporting)
Note: Reporting is ad-hoc, may involve full table scans and does not involve
Analytics. Data size is huge 2TB (OLTP+Reporting) per node.
Hardware : Standard deployment -3 node cluster with each node having 24 cores,
64GB RAM, 400GB * 6 SSDs in RAID5
Proposed Solution:
1. Split OLTP and Reporting clients into two application components.
2. For small deployments where more than 3 nodes are not required:
A. Install 2 Cassandra instances on each node one for OLTP and other for
Reporting
B. To distribute I/O load in 2:1 --Remove RAID5 (as Cassandra offers
replication) and assign 4 disks as JBod for OLTP and 2 disks for Reporting
C. RAM is abundant and often under-utilized , so assign 8GB each for 2
Cassandra instance
D. To make sure that Reporting is not able to overload CPU, tune
concurrent_reads,concurrent_writes
OLTP client will only write to OLTP DB and generate DB record. Reporting
client will poll FS and populate Reporting DB in required format.
3. Larger customers can have Reporting clients and DB on dedicated physical
nodes with all resources.
Key Questions:
Is it ok to run 2 Cassandra instances on one node in Production system and
limit CPU Usage,Disk I/O and RAM as suggested above?
Any other solution for above mentioned problem statement?
Thanks
Anuj
