Document support for CockroachDB

AC

• Add CockroachDB to the list of Supported Environments
• Add list of supported CockroachDB version(s) in Supported Environments page
• Document limitations and differences in behavior when using CockroachDB

Differences in behavior that should be documented

• OptimisticLockingException will be throw in different circumstances
  • If CRDB detects any concurrency conflicts that CRDB detects and aborts the transaction for (=> link to CRDB transaction docs)
  • Needs more investigation: Concurrent modification of separate data in the same table can lead to a concurrency conflict when CRDB enforces foreign key constraints (e.g. execution of two unrelated jobs)
• Cannot use engine property jdbcStatementTimeout: CRDB doesn't implement query cancellation yet (see https://github.com/cockroachdb/cockroach/issues/41335)
• There will be more failures with OptimisticLockingException due to stricter requirements for isolation Serializable
  • Historic {{OptimisticLockingException}}s are not silently ignored with CRDB
  • Job acquisition and external task fetch&lock failures are not silently ignored. => CRDB retry interceptor can be used
• Needs more investigation: check if tx timeout on CRDB is configurable; if not, then document this
• Pessimistic locks are useless for the purpose we are using them for; due to Serializable isolation, a parallel transaction will not observe changed data immediately after the pessimistic lock is granted
  • Pessimistic locks are disabled with CRDB
  • The retry interceptor can be enabled to avoid e.g. engine startup failures
  • Exclusive message correlation is not supported