1. University of Illinois at Urbana-Champaign
Parqua
Online Reconfigurations in
Ring-Based NoSQL Systems
Yosub Shin, Mainak Ghosh,
Indranil Gupta
University of Illinois at Urbana-Champaign
DPRG:

2. Ring-Based Key-value Stores
Growing segment in Industry (21% CAGR, $3.4 B by 2020)
Replacing traditional databases
Fast and highly available
Apache Cassandra (Facebook), Voldemort (LinkedIn), Riak (Basho), Dynamo (Amazon)…
Used widely
Amazon shopping carts (Dynamo)
Netflix (Cassandra) … 2

3. Reconfiguration Operations
Major pain point: Reconfiguration operations
Change that affects a lot of data in tables at once
Examples
Change key, e.g., SSN  Employee ID
[MongoDB JIRA Server-4000]
Scale out/in
Today’s solution: export DB, shut down DB, change configuration, re-import and re-start DB 3

4. Parqua System
Allows ring-based key-value stores to perform reconfiguration in online manner
Answering reads, writes and queries normally
While transferring data in the background among servers and committing 4

5. Background: Apache Cassandra – Virtual Ring5

6. Reconfiguration: Parqua Phases
I. Prepare Phase
Create new table
Column family (CF)
Old CF continues to
serve reads/writes 6

7. Reconfiguration: Parqua Phases
II. Execute Phase
Each node
Hashes its data
Sends it to new node in
new configuration
Appropriate replica 7

8. Reconfiguration: Parqua Phases
III. Commit Phase
Atomically swap between
old and new configs
Schemas
SSTables
Writes locked briefly 8

9. Reconfiguration: Parqua Phases
IV. Recovery Phase
Nodes catch up with
R/W received during
Execute phase
Activate new config. 9

10. Experiments Parqua: Maintains high availability under reconfiguration
multiple 9’s of availability
Has minimal impact on latency
50th percentile about the same
Tail slightly longer
Scales with database size and cluster size
Read (%)
Write (%)
Read only
99.17 –
Uniform
99.27
99.01
Latest
96.07
98.92
Zipfian
99.02 10
DPRG:

11. Backup Slides 11

12. Experiments
Effect on Read Latency 12

13. Experiments
Scalability (Database size)

14. Experiments
Scalability (Cluster size) 14