[GitHub] couchdb-couch issue #185: 3061 adaptive header search

[jaydoane <gi...@git.apache.org>]

Github user jaydoane commented on the issue:

    https://github.com/apache/couchdb-couch/pull/185
  
    I've been testing with this repl command:
    ```erlang
    _time_find_header = fun(File, Algorithm) when is_list(File) ->
        FileSize = filelib:file_size(File),
        {ok, Fd} = file:open(File, [raw, read, binary]),
        {Time, Result} = case Algorithm of
            current ->
                timer:tc(couch_file,find_header,[Fd, FileSize div 4096]);
            default ->
                timer:tc(couch_file,find_last_header,[Fd, FileSize]);
            adaptive ->
                ok = config:set_integer("couchdb", "chunk_max_size", 4096*4096),
                ok = config:set_integer("couchdb", "chunk_exponent_base", 2),
                Res = timer:tc(couch_file,find_last_header,[Fd, FileSize]),
                ok = config:delete("couchdb", "chunk_max_size"),
                ok = config:delete("couchdb", "chunk_exponent_base"),
                Res
        end,
        ok = file:close(Fd),
        case Result of 
            {ok, HeaderBin} ->
                {Time, binary_to_term(HeaderBin)};
            _ ->
                {Time, Result}
        end
    end.
    ```
    and use it like so:
    ```erlang
    (node1@127.0.0.1)78> _time_find_header("/Users/jay/proj/ibm/sample-data/foo.couch", current).
    {255,
     {db_header,6,0,0,nil,nil,nil,0,nil,nil,1000,
                <<"1ca5e7003114d27fa1dcfff52b10163f">>,
                [{'node1@127.0.0.1',0}],
                0}}
    (node1@127.0.0.1)79> _time_find_header("/Users/jay/proj/ibm/sample-data/foo.couch", default).
    {119,
     {db_header,6,0,0,nil,nil,nil,0,nil,nil,1000,
                <<"1ca5e7003114d27fa1dcfff52b10163f">>,
                [{'node1@127.0.0.1',0}],
                0}}
    (node1@127.0.0.1)80> _time_find_header("/Users/jay/proj/ibm/sample-data/foo.couch", adaptive).
    {138,
     {db_header,6,0,0,nil,nil,nil,0,nil,nil,1000,
                <<"1ca5e7003114d27fa1dcfff52b10163f">>,
                [{'node1@127.0.0.1',0}],
                0}}
    ```


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