http://d.puremagic.com/issues/show_bug.cgi?id=5198

           Summary: Appender much slower when appending ranges of elements
                    than individual elements
           Product: D
           Version: D2
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: schveiguy@yahoo.com


--- Comment #0 from Steven Schveighoffer <schveiguy@yahoo.com> 2010-11-10 11:23:42 PST ---
Given an appender Appender!string a, the following code should be roughly equivalent performance-wise:

a.put(' ');
a.put(" ");

But as shown by this code, the version that puts an individual character is an order of magnitude faster.

import std.stdio;
import std.date;
import std.array;

void f0()
{
    Appender!string a;
    a.reserve(100_000_000);

    foreach(i; 0 .. 100_000_000)
    {
        a.put(' ');
    }
}

void f1()
{
    Appender!string a;
    a.reserve(100_000_000);

    foreach(i; 0 .. 100_000_000)
    {
        a.put(" ");
    }
}


void main()
{
    auto r = benchmark!(f0)(1);
    writeln(r, "ms");
    r = benchmark!(f1)(1);
    writeln(r, "ms");
}

Results:
[2433]ms
[13276]ms

Swapping the order of testing does not change the situation.

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Andrei Alexandrescu <andrei@metalanguage.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|                            |andrei@metalanguage.com


--- Comment #1 from Andrei Alexandrescu <andrei@metalanguage.com> 2010-11-10 11:55:35 PST ---
Great catch! I'm marking this as "assigned" as I see you've already assign it to yourself.

Long term I wonder whether we should include performance tests as part of build acceptance tests.

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Steven Schveighoffer <schveiguy@yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


--- Comment #2 from Steven Schveighoffer <schveiguy@yahoo.com> 2010-12-27 11:20:47 PST ---
turns out the appender was not reserving any extra space when appending an array, it was simply reallocating -- just enough to hold the existing data + the new data (in this example, 1 more element).  I fixed it so the same algorithm used to expand the array for one element is now used to append an array of elements.

changeset http://www.dsource.org/projects/phobos/changeset/2237

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