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eulerto / wal2json

JSON output plugin for changeset extraction
BSD 3-Clause "New" or "Revised" License
1.33k stars 161 forks source link

Sequence of decoding #32

Closed rugging24 closed 7 years ago

rugging24 commented 7 years ago

Hello, This is more of a question than an issue. Assuming I have 3 concurrent transactions A,B and C all started at the same time x. B happens to commit before A , and A commits before C. So the commit order is something in the line of :

B,A,C.

giving they are commit at different times, do they all get decoded in the same order of commit. Or is it possible that in an environment with high concurrency , it's possible that the decoding is not strictly followed by the order/time with which each transaction was committed ?

If it happens that the transaction could be decoded regardless of their commit time , then it does suffice to say that the transaction commit time is not a sure way to track consumed messages and start replaying from where one left off. Is it then possible to have the LSN number for both a begin and a commit statement ?

I know in the current setup of wal2json and the output messages, the begin header , transaction message and the commit header are all in a single message making it impossible to track the commit LSN.

Could you please shed some light on this topic ?

regards,

rugging24 commented 7 years ago

--- With the LSN enabled everything should be fine.