TransactionManager#startTransactions API.

[jkozlowski]

Goals (and why):

• Return OpenTransaction that knows how to close the transaction wrt. open resources.
• Remove start/finish pair of methods that is very C-like.
• Hide the immutable timestamp lock token.
• OpenTransactions can contain any lockwatch-related methods, so they do not have to be exposed outside of this flow, as it doesn't make sense otherwise.

Implementation Description (bullets):

Testing (What was existing testing like? What have you done to improve it?):

Concerns (what feedback would you like?):

• It feels like an improvement, but there might be something even more drastic.

Where should we start reviewing?:

Priority (whenever / two weeks / yesterday):

[changelog-app]

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Type

• Feature
• Improvement
• Fix
• Break
• Deprecation
• Manual task
• Migration

Description

Add TransactionManager#startTransactions API that replaces previous #setupRunTaskBatchWithConditionThrowOnConflict and #finishRunTaskWithLockThrowOnConflict.

Check the box to generate changelog(s)

• Generate changelog entry

[jeremyk-91]

Preliminary feedback (only scanned, didn't review impl in depth)

OpenTransaction

• Broadly makes sense. In general no reason to expose the immutable timestamp thing
• Just make sure to check this won’t actually break anyone; backup services and migration lib are probably going to touch immutable timestamps in some way, so I’d imagine they’d be higher risk. (Though they might not go through TMs, in which case they’re fine)

OpenTransactions plural

• I’d interpret OpenTransactions as List + maybe some derived things, including LockWatch stuff there seems a bit unexpected. (In a good number of contexts (large internal product, embedded) we won’t have and won’t use the Events.)
• Yet we certainly do want this structure. Maybe if we named it StartTransactionsResponse I’d find this to be less conflicting with my intuition?

[jeremyk-91]

For the most part this makes sense. Some minor questions

[jeremyk-91]

👍