[Noob] veiled passage in "Consensus on Transaction Commit"

[Alexander Vasilev]

Hello.

I'v read "Consensus on Transaction Commit" (a spinoff of "The TLA+ Video Course") through and found a veiled passage.

Section 2 "Transaction Commit" on page 2 starts as follows:

In a distributed system, a transaction is performed by a collection of processes called resource managers (RMs), each executing on a different node. The transaction ends when one of the resource managers issues a request
either to commit or to abort the transaction.

The naive reader (that's me!) would expect rather

The transaction starts when one of the resource managers issues a request...

Compare this with section 4.2 "The Paxos Commit Algorithm" on page 11:

Execution of Paxos Commit normally starts when some RM decides to prepare and sends a BeginCommit message to the leader.

or section 6.3 "Committing a Transaction" on page 18:

In Two-Phase Commit, the BeginCommit message is the Prepared message of the first RM to enter the prepared state.

so the start of the transaction is marked by sending the Prepared/BeginCommit message in case of Two-Phase/Paxos Commit. Isn't it the "request either to commit or to abort"? Alas, there is no message at the Transaction Commit abstraction level. When I started to search the "request either to C or to A", I was really puzzled. Does the request correspond to the transition from "working" into "prepared" state on Figure 1 (page 3), i.e. Prepare action in The Specification of a Transaction Commit Protocol? Or does the request correspond to the Decide action in the same Specification? It the latter case the request ends transaction indeed.

[Leslie Lamport]

This does appear to be a typo.  Unfortunately, I don't know how to post a corrected version on the paper's current location.  I will try to find out.

Leslie

[Amir A.H.S.A]

Hi,

In the case of Transaction Commit spec (TCommit), there is no Transaction Manager and therefore there is no need to send/receive messages. Each RM will independently change its current state to the next state, and it uses "canCommit" and "notCommitted" as a means to abstract the unnecessary complexity of sending/receiving messages.

As to your specific question, the start of a transaction is marked by an RM that changes its current state from "working" to "prepared".

Please let me know if this helps.

Sincerely,

Amir Hossein Sayyad Abdi

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[Alexander Vasilev]

Dear Mr. Lamport, Mr. Abdi

Thank you for your replies. The issue is settled.

четверг, 9 мая 2019 г., 14:57:01 UTC+7 пользователь AmirHossein написал:

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