Calle Wilund dcabf8c1d2 Commitlog: Pre-allocate "reserve" segments ...

Refs #356

Pre-allocates N segments from timer task. N is "adaptive" in that it is
increased (to a max) every time segement acquisition is forced to allocate
a new instead of picking from pre-alloc (reserve) list. The idea is that it is
easier to adapt how many segments we consume per timer quanta than the timer
quanta itself.

Also does disk pressure check and flush from timer task now. Note that the
check is still only done max once every new segment.

Some logging cleanup/betterment also to make behaviour easier to trace.

Reserve segments start out at zero length, and are still deleted when finished.
This is because otherwise we'd still have to clear the file to be able to
properly parse it later (given that is can be a "half" file due to power fail
etc). This might need revisiting as well.

With this patch, there should be no case (except flush starvation) where
"add_mutation" actually waits for a (potentially) blocking op (disk).
Note that since the amount of reserve is increased as needed, there will
be occasional cases where a new segment is created in the alloc path
until the system finds equilebrium. But this should only be during a breif
warmup.

v2: Fixed timestamp not being reset on reserve acquire

2015-09-21 13:04:39 +02:00

9.5 KiB

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