The section should cover the following:

• Non-retryable internal transactions
• Retryable internal transactions
  • How retryablity works
    • The “stmtId”, “preImageOpTime”, “postImageOpTime”, “needsRetryImage” fields in the inner oplog entries inside each applyOps oplog entry.
    • How each retryable write statement generates only one operation entry with its stmtId; any other operation entries have stmtId=-1.
    • How each internal session can only have one retryable findAndModify. 
      refreshFromStorageIfNeeded() and RetryableTransactionParticipantCatalog.
    • How concurrent retries are prevented (i.e. RetryableTransactionInProgress).
  • Session migration during chunk migration and resharding
    • Retryability contract.
    • How retryable internal transaction oplog entries are converted to retryable write oplog entries.