Avi Kivity 9ac730dcc9 mutation_reader: make restricting_mutation_reader even more restricting ...

While limiting the number of concurrently executing sstable readers reduces
our memory load, the queued readers, although consuming a small amount of
memory, can still grow without bounds.

To limit the damage, add two limits on the queue:
 - a timeout, which is equal to the read timeout
 - a queue length limit, which is equal to 2% of the shard memory divided
   by an estimate of the queued request size (1kb)

Together, these limits bound the amount of memory needed by queued disk
requests in case the disk can't keep up.
Message-Id: <1467206055-30769-1-git-send-email-avi@scylladb.com>

2016-06-29 15:17:35 +02:00

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