How do I choose H2, a host database, or a modern database after migration?

OL Next runs the replatformed programs off the host. Data is a separate choice.

• Sandbox (H2) — isolated play; populate from schema.sql and seed.sql. Use when you do not want a host or production store.
• Legacy DB — keep data on DB2, VSAM, or IMS-DB. Connect with JDBC, or through OL CoreIQ APIs (DB2 table APIs, VSAM dataset APIs, IMS-DB JDBC). Use when logic has left the host but data has not.
• Modern DB — point the same programs at the post-migration store. Use when data migration is done.

Play failures usually mean the connection is missing, credentials are wrong, or the schema the program expects is not on that target. See DB access management.