Asymmetric Capacity Expansion for Travel Agency Booking


An outsource provider of services for various travel booking agencies faced a severe capacity problem each year during the holiday season. Many of its customers wanted to go on vacation and were comparing rates and availability prior to actually booking a trip, generating on average over 700 “looks to one book”. All of this look-to-book activity caused query processing to increase from five to fifty times the normal query load, which greatly impacted the capacity of the HPE NonStop booking system. Recognizing that actual booking activity involved 80%-90% complex queries and 10%-20% simple writes, the provider wanted to replicate the booking system’s master database to NonStop and Windows target systems that support the travel agent queries.

Shadowbase Solution: Asymmetric Capacity Expansions


  • The outsource provider’s application is configured (no application modification was required) to perform all queries against the replicated targets, yet still apply the booking transactions to the master booking node.
  • Additional query node replicates can be added as the query volume increases.
  • The key structure on the master booking node remains optimized for OLTP access (“skinny” keys), and the key structure on the query node is optimized for query (“fat” keys).
  • Data from the master booking node is replicated to Windows Servers running MSSQL, which supports a large Operational Data Store (ODS) application.

Additional Benefits:

  • Backup Disaster Recovery
  • Each of the NonStop read-only query nodes acts as a disaster recovery backup for the NonStop master node.
  • The entire database resides on each of the read-only nodes, in essence allowing the provider to scale the application across multiple systems and provide disaster recovery “for free.”
  • In the event of a master booking node failure, one of the query nodes can be promoted to be the new master.

Contact us for more information on this Shadowbase solution.

The above was adapted from the book: Breaking the Availability Barrier, Volume III: Active/Active Systems in Practice by Paul J. Holenstein, Dr. Bruce Holenstein, and Dr. Bill Highleyman.