Remove local static string

[burtonli]

Local static string is not friendly to Jemalloc arena aware implementation, as it will be allocated on the arena of the first caller, which causes crash if the allocated arena gets refunded earlier.

P.S. A Jemalloc arena aware implementation is each rocksdb instance only use certain Jemalloc arenas, and arena will be refunded after associated DB instance is destroyed.

[ajkr]

To support this use case, it sounds like we would have to disallow local static variables that allocate memory. It sounds like an odd restriction - is this correct, and is there another way?

[burtonli]

To support this use case, it sounds like we would have to disallow local static variables that allocate memory. It sounds like an odd restriction - is this correct, and is there another way?

It's ok to have local static variable without heap memory allocation, and it's also ok to have local static variables in global instance, e.g. those singletons like the implementation for Env::Default(), SystemClock::Default(), so that user can explicitly call the constructor from the environment arena (the one last as long as the process).
I agree we may not want to add the restriction to prohibit local static var, but I think the removed ones in the PR are not necessary.

[ltamasi]

Thanks for the PR @burtonli !

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