BIND 10 #2831: define and implement MemorySegmentMapped

[BIND 10 Development]

#2831: define and implement MemorySegmentMapped
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            Reporter:  jinmei        |                        Owner:
                Type:  task          |                       Status:  new
            Priority:  medium        |                    Milestone:  Next-
           Component:  data source   |  Sprint-Proposed
            Keywords:                |                   Resolution:
           Sensitive:  0             |                 CVSS Scoring:
         Sub-Project:  DNS           |              Defect Severity:  N/A
Estimated Difficulty:  0             |  Feature Depending on Ticket:
         Total Hours:  0             |  shared memory data source
                                     |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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Comment (by jinmei):

 Replying to [comment:4 jinmei]:

 > > Usually, these things are done with doubling the size. Then you have
 at most half of the size wasted and the amortized amount of work done per
 adding one byte to it is constant.

 > Yeah, but I was not sure if that's what we want in this case; for a
 > large zone it can be several GBs, which will eventually be mapped to
 > real memory.

 I've added another wrapper for the underlying managed_mapped_file:
 `shrinkToFit`.  Using this would probably address my concern: on grow
 we simply double the size, and after a set of operations call
 `shrinkToFit`.

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Ticket URL: <http://bind10.isc.org/ticket/2831#comment:7>
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