On 10/28/2016 08:00 AM, he.yu...@zte.com.cn wrote: > so we need to public the DataTreeCandidateTip.getTipRoot() API in > yangtools to get the last tx's root > > All of the above is not related to commit phase, the overall process is > as follows > > > Tx1.prepare() ---> Tx1.candidate > Tx1 persist ReplicatedLogEntry > Tx1 add to pipelineTransactions > Tx2.prepare(Tx1.candidate) ----------> Tx2.candidate
Actually the flow should be:
TipProducingDataTree dataTree;
DataTreeCandidateTip tx1Candidate = dataTree.prepare(tx1);
persist tx1Candidate
DataTreeCandidateTip tx2Candidate = tx1Candidate.prepare(tx2);
persist tx2Candidate
dataTree.commit(tx1Candidate);
dataTree.commit(tx2Candidate);
All of the accounting needed will occur inside the DataTree
implementation without leaking tipRoot. The API has been explicitly
designed for this use case -- it just has not been implemented yet,
because appendAndPersist() is synchronous and the surrounding code
assumes that once the candidate has been persisted, it has also been
committed.
For this to work correctly in face of failures and recovery, there need
to be further persist events and frontend replies need to be sent as
following:
- once candidate persist completes, notify fronted of precommit success,
wait for commit message (or shortcut in directCommit case)
- once commit request arrives (or 3PC commit timer expires):
dataTree.commit()
persist tx commit record (only identifier, no data)
- once persist returns:
notify frontend of commit success
And on follower/recovery, the journal records need to be processed in a
similar fashion: candidates should be committed to data tree only when
commit record is seen. There can be multiple candidates for a
transaction in the journal (due to failovers and similar), hence only
the last candidate seen should be committed.
Bye,
Robert
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