This issue tracks the implementation of the connection migration mechanism, as described in this RFC: #75707.

• add postgres interceptor for message forwarding (ccl/sqlproxyccl: add postgres interceptors for message forwarding #76006)
  • update PeekMsg to return message size instead of body size. See comment here. (ccl/sqlproxyccl: update PeekMsg to return message size instead of body size #76562)
• add SHOW TRANSFER STATE [ WITH <transfer_key> ] observer statement (sql: add SHOW TRANSFER STATE observer statement #76127)
• refactor connection establishment logic into a connector component (ccl/sqlproxyccl: add connector component and support for session revival token #76417)
• add basic forwarder component with ConnectionCopy logic (ccl/sqlproxyccl: add basic forwarder component #76167)
• update ConnectionCopy logic to use interceptors (ccl/sqlproxyccl: replace ConnectionCopy logic in forwarder with interceptors #76560)
• add token-based auth into connector component (ccl/sqlproxyccl: add connector component and support for session revival token #76417)
• add migration logic to forwarder (ccl/sqlproxyccl: complete connection migration support in the forwarder #76805)
  • cleanup interceptor API (ccl/sqlproxyccl: cleanup PG interceptor APIs #76613). It was difficult to update the destination of interceptors without this.
• observability: metrics and logging (See ccl/sqlproxyccl: complete connection migration support in the forwarder #76805)
  • "There should be metrics tracking the number of failed transfers and the number of connections closed mid-transfer. The metrics should be visible on the sqlproxy grafana page."
  • The grafana updates will be part of CC, and will be omitted here.
• Attempt to refactor expectNextServerMessage again. The approach of us checking the message size can be confusing as-is here. (ccl/sqlproxyccl: add helpers related to connection migration #77109)
• Add metrics to measure DataRow size. This will allow us to figure out what's the right size. (ccl/sqlproxyccl: add connection migration-related metrics #77700)
• clean up interceptor benchmarks (ccl/sqlproxyccl: add benchmarks for connection copying logic  #76429)
• clean up TenantResolver interface (ccl/sqlproxyccl: rename tenant.Resolver to tenant.DirectoryCache  #78276)

Related Epics:

• https://cockroachlabs.atlassian.net/browse/CC-5385
• https://cockroachlabs.atlassian.net/browse/CC-5387

Jira issue: CRDB-12912