A Comparative Evaluation of Transparent Scaling Techniques for Dynamic Content Servers Presented by Chen Zhang Written by C. Amza, A. L. Cox, W. Zwaenepoel

Overview What does the paper do? Designed a DB cluster architecture oriented at dynamic content web sites Evaluated transparent scaling technique combinations against TPC-W Experimental Findings TPC-W scales well with cluster size increase Conflict-aware scheduling with most beneficial impact Load balancing has secondary impact Optimizing for locality has no impact

Myth … Replication Load balancing Caching Scheduling

Who is who Sch Scheduling Caching Seq Adding sequence number DP Query queuing for ordering Admission Control DB Consistency 1-copy-serializability

Scheduler and DP Scheduler Parse individual queries – context-aware Backlog for all replicated ops for active trans. Current load of DB Consistency among other schedulers DP Conflict-aware Lock tables, not passed to DB In order Out-of-order Query prioritizing (a little bit of scheduling) Admission Control

Scheduling and load balancing Scheduling Synchronous Replication Content-Aware asynchronous replication Conflict-aware deadlock avoidance At DP, “lock tables” Load balancing Generic: Round Robin, Shortest Queue First Content-aware –Shortest Execution Length First (SELF) –Locality-aware Request Distribution (LARD)

Caching Happen at schedulers Function Cached query results for all reads Forwards “lock tables” Constraint Require low write frequency Size LRU as Replacement strategy Consistency between different scheduler cache.

Experiment TPC-W Benchmark Cluster max 8 DB machines 2 schedulers Software Apache PHP Mysql Tested Combinations Base BestSync ConflA ConflACache

Discussion Recall Ganymed Scaling Cache Dynamic content replication About scheduler and DP About degree of consistency ……