What we did in the old implementation was pure over-engineering.
We relied on CoreDB's `Drop` impl to terminate the background services.
Now this is absolutely unreliable due to the nature of async functions.
We also relied on the bgsave scheduler to release the lock upon exit
which is also unreliable because we left the service to the mercy of the
runtime. We spawned the task and didn't hold as much as a `JoinHandle`
to it. That's bad because the runtime can just abort these tasks which
may result in the lock never being released. Even though it is designed
to release the lock on Drop, the destructor may however not be called at
all.
This commit fixes all those issues by simplifying the entire impl to
use Terminator. Now the background save and snapshot services run
independently, in their own tasks. Whenever the user passes a SIGINT,
we tell everyone to quit. The listeners understand that this is the
last query they'll process and the background save tasks exit almost
immediately. But what if some data was modified by this last query...?
No worries, that is completely handled by main(). The lock that BGSAVE
leaves is immediately (almost) returned to main and main will attempt
to flush the data almost immediately. That's how we maintain reliability
This commit ensures that BGSAVE is optimistic in doing what it is doing:
If BGSAVE fails once, it will immediately poison the table. Now let's
say that some amazing sysadmin managed to SSH into the server and was
able to fix the storage issue; BGSAVE would be able to succeed.
The current implementation was flawed: firstly it prevented that and
secondly even if it succeeded in running BGSAVE, the server would refuse
to accept writes. This commit fixes this behavior.
The size part of the metaline is absolutely redundant as we're doing
double the work while reading the size and then the real thing.
Since sizes won't have escape codes, we can freely read upto the LF
Sayan Nandan