Hi Daniel， I think current solution is checking the credit as a resource to make sure the amount of transfer is below the credit first in the try phase or the transaction phase.
After going through the Chris saga talk[1], there are some interesting pages[2]. I'm highly recommend you to read about it. There is some countermeasure about how to solve the isolation issue in the paper. Maybe we can consider to implement in our project. [1] http://microservices.io/microservices/general/2018/03/22/microxchg-sagas.html [2]http://bit.ly/semantic-acid-ctm Willem Jiang Blog: http://willemjiang.blogspot.com (English) http://jnn.iteye.com (Chinese) Twitter: willemjiang Weibo: 姜宁willem On Fri, Apr 6, 2018 at 4:40 PM, Daniel Qian <[email protected]> wrote: > @Eric Lee. As the bank money transferring example you gave, how can a > developer > prevent overdrawing problem? > > BTW, I think at a certain time point, customer finds out an > "inconsistency" result is > quite intuitive, that shouldn't be considered as a problem. > > 2018-04-03 16:04 GMT+08:00 Zheng Feng <[email protected]>: > > OK, let's JIRA it at first. > > > > 2018-04-03 15:47 GMT+08:00 Willem Jiang <[email protected]>: > > > >> Hi Feng > >> > >> After go through the wiki page of MVCC[1], it looks like we are doing > the > >> same thing with the help of database. > >> Can you elaborate using the wrapper class with the database driver? > >> Currently I don't want to interpret the SQL to do this kind of work. > >> > >> [1]https://en.wikipedia.org/wiki/Multiversion_concurrency_control > >> > >> > >> Willem Jiang > >> > >> Blog: http://willemjiang.blogspot.com (English) > >> http://jnn.iteye.com (Chinese) > >> Twitter: willemjiang > >> Weibo: 姜宁willem > >> > >> On Tue, Apr 3, 2018 at 11:07 AM, Zheng Feng <[email protected]> wrote: > >> > >> > In the term of hiding the temp table, I think we can provide a wrapper > >> > class with the database driver. And I'm not sure if we are looking for > >> > something like MVCC ( Multi-Version Concurrency Control ) ? > >> > > >> > 2018-04-02 22:54 GMT+08:00 Willem Jiang <[email protected]>: > >> > > >> > > Chris just gave a talk[1] recently about the countermeasure for data > >> > > anomalies. > >> > > It made us to think if we can find a better way to resolve the > >> isolation > >> > > issues. > >> > > > >> > > It looks like the TCC pattern can prevent the uncommitted states to > be > >> > saw > >> > > by adding the try phases. > >> > > And this is what current saga solution is missed. With help of temp > >> > table > >> > > to store the status of the try operation, we don't need the > coordinator > >> > > handle much unnormal situation. It could be better if we don't let > >> the > >> > > user know about the temp table. But the challenge is how can we hide > >> the > >> > > temp table to the user. > >> > > > >> > > [1] > >> > > http://microservices.io/microservices/general/2018/03/ > >> > > 22/microxchg-sagas.html > >> > > > >> > > > >> > > > >> > > Willem Jiang > >> > > > >> > > Blog: http://willemjiang.blogspot.com (English) > >> > > http://jnn.iteye.com (Chinese) > >> > > Twitter: willemjiang > >> > > Weibo: 姜宁willem > >> > > > >> > > On Mon, Apr 2, 2018 at 5:57 PM, Eric Lee <[email protected]> > >> wrote: > >> > > > >> > > > Hi, all > >> > > > > >> > > > As we have discussed the ACID guarantees Saga provides in the > >> previous > >> > > > thread[1], it turns out Saga does not provide isolation > guarantee. To > >> > > > improve user experience, the business logic using Saga may need to > >> > > reorder > >> > > > to make sure the user-sensitive sub-transaction is the last one > to be > >> > > > executed. In sceanrios require full ACID support, the > implementaion > >> of > >> > > Saga > >> > > > may need to be compatible with the TCC[2] pattern with an extra > try > >> > > phase. > >> > > > > >> > > > Take a transfer application as an example, it contains transfer in > >> and > >> > > > transfer out service of two different databases. From the > customer's > >> > > view, > >> > > > the transfer in and transfer out operation is an atomic operation > >> which > >> > > > requires both to be executed or nothing executed. However, in the > >> > middle > >> > > of > >> > > > the overall transaction, e.g. the sub transaction of transfer out > is > >> > done > >> > > > and the sub transaction of transfer in is not done yet, if a > customer > >> > > > checkouts out his/her balance, it will become weird as the > balance is > >> > not > >> > > > equal. The isolation is corrupted at this moment in Saga. > >> > > > In TCC, the isolation could be solved using either the > reservation > >> or > >> > > > compensation which depends on your bussiness logic. > >> > > > Reservation: In try phase, use a temporal table to store the > credit > >> and > >> > > > transaction context. In commit phase, reduce the balance in the > >> account > >> > > and > >> > > > remove the temporal table. If anything goes wrong, it can execute > the > >> > > > cancel method to remove the temporal table. In this way, if the > >> global > >> > > > transaction fails, it will take no effect on the actual table. > >> Besides, > >> > > > when a customer visits his/her balance, we can simply return the > >> value > >> > in > >> > > > the actual table which is the original value before this > transaction > >> > > > executed. > >> > > > Compensation: In try phase, use a temporal table to record the > >> > > compensated > >> > > > value and reduce the balance in the account. In commit phase, > remove > >> > the > >> > > > temporal table. If anything goes wrong, it can execute the cancel > >> > method > >> > > > to recover the balance according to the temporal table and remove > the > >> > > > temporal table afterward. In this way, when a customer visits > his/her > >> > > > balance, we can do simple calculation of the value in actual table > >> and > >> > > > temporal table to return the origianl value before the transaction > >> > > > executed. > >> > > > > >> > > > Within transaction ids in the table row, each create/update/delete > >> > > > operation is idempotent and it simplies a lot of work to make sure > >> > > > sub-transactions are idempotent. > >> > > > > >> > > > > >> > > > Any other ideas or suggestions on the isolation support in Saga > are > >> > > > welcome. Thanks. > >> > > > > >> > > > > >> > > > [1] https://lists.apache.org/[email protected] > >> > > > e.org:lte=1M:a%20question%20about%20acid%20 > >> > > > [2] http://design.inf.usi.ch/sites/default/files/biblio/ > rest-tcc.pdf > >> > > > > >> > > > > >> > > > Best Regards! > >> > > > Eric Lee > >> > > > > >> > > > >> > > >> > > > > -- > > > > Daniel Qian >
