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Scheduled-style mechanism
This group of approaches is based on periodic scanning of all saved pieces and determining the status of poline PO line on this basis. A typical algorithm for such mechanism might look as shown on Figure 1.
Figure 1 - A general algorithm of mechanisms based on periodic scanning of the entire set of pieces.
Particular implementations of this approach are presented below.
Vert.X Periodic Timer
Within the Vert.X features #_executing_periodic_and_delayed_actions one can implement a mechanism that periodically retries the pieces and checks the status of the polinePO line, changing it if necessary. There is a need to develop a mechanism that monitors pieces status in cluster mode, when each mod-orders / mod-orders-storage instance will start the scheduler entity. Thus, it is necessary to provide a solution so that the instances of the scheduler from each mod-orders / mod-orders-storage do not compete and do extra pieces checking.
Separate Scheduler Application
Since this will be a separate application it will solve the problem of multiple instance of scheduler noted in the previous option.
PostgreSQL cron-job
Task scheduler can be installed as PostgreSQL DB extension that executes scheduled tasks directly from the database, for example, pg_cron. This will allow to run poline PO line status verification task following the algorithm from Figure 1 and implemented as a sequence of PostgreSQL commands.
Interceptor-style mechanism
This group of mechanisms is based on the injection of logic into the process, which checks the status of poline PO line and its associated pieces. This logic checks the consistency of statuses and provides poline PO line status changes, if necessary. The algorithm looks as shown on Figure 2.
Figure 2 - A general algorithm of mechanisms based on consistency checking as part of retrieving flow.
Checking and updating the PO line status upon retrieving
During poline PO line retrieving one can check whether its status corresponds to the state of the associated pieces according to algorithm from Figure 2 and on this basis to decide on updating the status of poline PO line. However, within the framework of this approach, there is a need for many additional steps associated with retrieval retrieving pieces, analysis of their status, changing and updating the poline PO line status every GET poline PO line request. As a result, this will lead to poor performance due to a potential UPDATE request at time of GET poline PO line request.
PostgreSQL Trigger Functions
A similar scenario can be made using the trigger function https://www.postgresql.org/docs/9.2/plpgsql-trigger.html that will be called for each state changing of pieces and make update the status of poline PO line if necessary - poline PO line data is updated when the underlying piece records are updated.
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The group of mechanisms for intercepting the change of state of pieces is associated with the lack of the need to perform additional operations, which will greatly affect performance.
A group of scheduled checkers seems to be the most appropriate, as it has less impact on performance.
Creating cron-jobs can be effective, but it is difficult to implement and maintain, since it is necessary to install an extension on each database.
Vert.X Periodic Timer seems to be the most efficient and easily implemented way, taking into account, however, the need to implement a way to coordinate instances to prevent unnecessary work in the case of a cluster.
Separate Scheduler Application can be an efficient way without the lack of lack of consistency in cluster mode (noted mentioned for Vert.X Periodic Timer) but it should technically be implemented probably as a separate module.