Page Comparison

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hard to predict what scheduled task will be executed next (yes, we have "Scheduled Tasks" grid, but due lots of information displayed there it takes time to figure that out)
[system log, scheduled tasks] Logging ability for Scheduled Tasks - any output produced (e.g. what data being processed, what errors might have happened) by currently running scheduled task is not logged anywhere
all scheduled tasks are processed one after another and if one of them crashes, then all others won't be processed as well
no parallelization can be applied in scheduled task execution, because they gather data to process by themselves and therefore will basically process same data if tried to execute in parallel

Solution

Create "ScheduledTaskData" database table with following structure:
- Id
- TaskClass - scheduled task class
- TaskData - a set of data to be processed by scheduled task class mentioned
- PlannedStartedOn - when scheduled task will be executed
- StartedOn - when scheduled task executed was started (start time)
- FinishedOn - when scheduled task finished executing (even in case of error)
- CreatedOn - when task record was created
- RegularOutput - any output made during task handling
- ErrorOutput - any errors happened during task handling
- Status - {1 - Not Started, 2 - Finished Successfully, 3 - Finished with Errors}
- ProcessId - the PID of the process, that is handling (or was handling in past) this task
create an AbstractScheduledTask base class with following methods:
- generate() - will collect data to be processed (e.g. DB record IDs or file paths on disk) and create a record in ScheduledTaskData table
- process($task_data) - will process the given task data
sub-class AbstractScheduledTask for each current scheduled task
scheduled task handling would look like this:
1. generate task data for all scheduled tasks
2. start processing the tasks if any (preferable in separate processes, not forks) in parallel to handle incoming task pool

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single scheduled task now has all it's execution attempts recorded and we need to be able to see them all, especially ones that failed
when there is no data to process we won't be incrementing "Last Run On" field in each scheduled task to indicate that it at least was executed but did nothing
since we'll generate several task data records per scheduled task upfront, when we can, then "Next Run On" column becomes irrelevant as well
past scheduled task runs without errors (e.g. more than 1 month old) can be deleted automatically as well
if the error happened during some scheduled task handling, then main scheduled task grid should clearly indicate that and maybe we need to send e-mail to admin as well