OpenWorld 2017: Split Your Database: Seamless Database Growth with MySQL

Nicolai Plum from Booking.com gave a presentation on how to split a database into multiple databases while minimizing/managing the impact to applications using it.  There is no voodoo magic, but it was a great session covering how to work with the application developers to split a database.

  • Stated with sales DB
    • Customers
    • Transactions
    • Delivery
    • Catalog
    • Inventory
    • Reviews
  • Breaking out the Product information
    • Catalog
    • Inventory
    • Reviews
  • Good idea to change schema name as you go to avoid confusion
  • Why
    • size
    • query time
    • regulatory requirements
    • business/architecture reasons
  • “GDPR best practice is to split private information away from non private information”
  • How to choose tables
    • minimize joins
    • Maximise gains
      • split out bigger, fastest growing, business, most regulated
      • size and activity use: ps-top (utility to help figure this out)
  • Code changes needed
    • may be able to use ProxySQL (has not tried it)
    • try to separate read and write traffic
  • “Everyone has a test environment, some people have a production one as well”
  • Use binlog to help
  • Get rid of joins in updates
  • joins move from sql to app code
  • foreign keys across servers will not work – relational integrity checks move up to app layer
  • uses a translation master to move data between the two schema
    • uses replicate-rewrite-db
    • uses replicate-wild-do-table
  • Steps to create translation master
    • Make a slave, with binlog enabled
    • shut down MySQL
    • configuration: Add
      • skip-slave=start
      • replicate-rewrite-db=’sales=>product’
      • replicate-wild-do-table…..
    • Create new schema
    • Rename all tables that are being split to the new schema
    • Drop old schema from translation master
    • start replication slave
    • Remove skip-slave-start
    • If replication stops with missing table errors, find the bad query, fix up (skip) or make a new translation master
  • Add product schema on sales master to allow product to read and write to the same schema name
    • use sys;
    • call create_synonym_db(‘sales’, ‘product’);
  • Need views in slaves also
  • Now ready to remove translation master and cut over to the new product replication topology
  • Need to fix up grants – they don’t replicate through translation master
    • use different user names to avoid collisions/confusion
  • Now cut the name over – either push config or use DNS CNAME or A record  update
  • Tradeoffs with cut over
    • Disconnect first to have cleanest cut over but with a little downtime
    • Disconnect last to keep application up but with risk of collisions

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