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From: Fionn Mac Cumhaill <invisible@hiding.from.spam>
Newsgroups: comp.lang.ada
Subject: Reading and writing a big file in Ada (GNAT) on Windows XP
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Date: Sat, 28 Apr 2007 05:03:48 GMT
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Date: 2007-04-28T05:03:48+00:00
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I have written a very simple program that runs  on a Windows XP
machine. (Pentium D , I don't remember the clock speed, it is in
middle of Pentium D clock speeds, 2 Gb memory) It is compiled with the
MinGW GNAT 3.4.5 Ada compiler.

All it does is read lines in a loop from a text file with
Ada.Text_IO.Get_Line, does minor modifications on about 80% of the
lines that it reads, and writes the lines to an output file with
Put_Line. 

The modifications consist of replacing a slice of text at the end of a
line with another bit of text. The biggest slice is 10 characters, and
the replacement slice is always smaller than the original slice. An
occasional line of text is about 6000 characters long, but most are
about 700 haracters.  Get_Line reads them into a String variable that
is 10,000 characters long.


The problem is that the input file has more than 10 million lines of
text in it. The program works perfectly, but takes about 5 hours to
run. The Cygwin version of wc can count the lines in the input file in
less than one minute.

The program that produces the file pulls data from a SQL Server 7
running on an 800 MhZ Pentium III machine with 512 Mb and writes it to
a file in 1-1/2 hours. Almost all (99.9%) of the lines are rows from a
database table.

Why is this so slow? 
Do I have an Ada problem, a GNAT problem, or a MinGW problem?