PostgreSQL JSONB Indexing Strategies for Mobile API Backends

Deep dive into how mobile backends abuse JSONB columns as a 'schema-free' escape hatch, then suffer catastrophic query performance at scale. Cover GIN index internals (posting trees, pending lists, fastupdate tradeoffs), the @> containment operator vs ->> extraction and why only one uses your index, expression indexes on JSONB paths for equality lookups, trigram indexes for LIKE queries inside JSON text fields, and the TOAST decompression cost that makes wide JSONB rows murder your p99 latency. Include EXPLAIN ANALYZE walkthroughs showing index selection behavior, the jsonpath alternative in PG 17, and concrete migration patterns for teams moving from schemaless JSONB to a hybrid normalized+JSONB model without downtime.