Transaction Handling Storage XL Coordinator Parser Planner Executor “Metadata” Storage XL Datanode Executor Storage Postgres Conference China 2016 中国用户大会 Postgres-XL Technology • Users connect Proc 2 GTM Postgres Conference China 2016 中国用户大会 GTM Proxy • Runs alongside Coordinator or Datanode • Backends use it instead of GTM • Groups requests together • Obtain range of transaction ids (XIDs) read mainly tables • Sometimes good for dimension tables in data warehousing • If coordinator and datanode are colocated, local read occurs • Bad for write-heavy tables • Each row is replicated to all